The grow reference that shows its sources.
Professor Greenleaf's library: answers first, numbers with units, a clinician's diagnosis order and a citation for anything that isn't common knowledge. When nobody knows yet, we say so.
BustedMythbusters: 17 grow myths, and the open trials →
The evidence ladder · how sure we are
- EstablishedMultiple studies or extension consensus
- SupportedSome research or strong grower consensus
- Grower practiceWidely used, little research
- ContestedEvidence points both ways
- MythWidely believed, not supported by evidence
Basics
Plant biology, life cycle, photoperiod vs auto, sex, first grows
Buyer beware: potency labels, strain names and other claims that don't hold up
Flower labelled above about 35% total cannabinoids is not credible: cannabinoids are made only in trichome heads, and bud is mostly bract, stem and leaf, so numbers like that belong to concentrates or to inflated testing. Studies show potency results vary systematically between labs, and retail flower labels often overstate THC. Be equally sceptical of strain names that promise effects, terpene totals far above the ~2% average, and 'indica for the couch, sativa for energy'.
Cannabis growing and breeding glossary
Plain-language definitions of the growing, botany and breeding terms used across GenetixBay, with notes where the popular meaning differs from the scientific one.
Cannabis plant biology: the parts and what they do
Cannabis sativa is a fast-growing annual herb in the hemp family. Most plants are either male or female, it flowers in response to long nights (unless it carries autoflower genetics), and the cannabinoids and terpenes growers want are made in glandular trichomes concentrated on the female flower heads.
Male, female and hermaphrodite cannabis: how sex works
Cannabis is dioecious: females are XX and males XY, and the species has kept separate sexes stably for millennia. Hermaphrodite (intersex) plants are unwanted outliers, mostly the result of bad breeding such as repeated selfing, careless feminising and untested seed; stress reveals the weakness in susceptible plants. Cull herm-prone plants and never breed from them. Seed from a female's own male flowers is almost all female, which is how feminised seed works and why herm tendency passes straight on.
Photoperiod vs autoflower, and how autoflowering is inherited
Photoperiod cannabis flowers when nights get long; autoflowering (day-neutral) cannabis flowers by age, even under 18-24 h light. In the populations studied so far, autoflowering behaves as a single recessive gene (Autoflower1, on chromosome 1): a photoperiod x auto F1 is all photoperiod, and about 1 in 4 of its F2 plants are autos.
Regular, feminised, autoflower or clone: choosing your starting material
Regular seed gives about half males and is what breeders need; feminised seed gives nearly all females and suits growers who want flower; autoflowers flower by age; clones copy one known plant but can carry pests and viroids. Each choice changes what you can do next.
Germination
Seed viability, germination, seedlings, damping-off, transplanting
Damping-off: why seedlings collapse at the soil line
Damping-off is seedling death caused mainly by soil-borne pathogens such as Pythium, Rhizoctonia and Fusarium: the stem pinches, darkens and collapses at the soil line, or seeds rot before emerging. It is a prevention problem: clean containers and new mix, no overwatering, warm medium, good light and airflow. Once a seedling has collapsed it cannot be saved.
Germination methods compared: soak, paper towel, plugs, direct sow
Cannabis seed germinates best around 20–30 °C (68–86 °F) with steady moisture and air. Every common method works if those are met: direct sowing is least handling, paper towels let you see radicles, plugs and cubes suit hydro. Lab protocols with 1 % hydrogen peroxide, short soaks or tip scarification sped up germination, mainly for old or hard seeds; they are optional for fresh seed.
Seed viability and storage: keeping cannabis seeds alive
Cannabis seeds stay viable longest when dry and cold: research on hemp and drug-type seeds recommends about 5 °C (41 °F) storage to keep germination ability for around six years, with low seed moisture and an airtight container. Room temperature and humid storage cost viability within months to a few years. Test old seeds with a small germination test before planting a whole batch.
Seedling care: the first three weeks
Seedlings need moderate light (about 150–300 µmol/m²/s, 18 h, a DLI of 10–19 mol/m²/day), warm and fairly humid air (23–27 °C / 73–81 °F, 65–75 % RH), and small, careful waterings. Most seedling losses come from overwatering, too little light (stretching) or damping-off, not from lack of nutrients. Start feeding lightly once the first two or three sets of true leaves have formed.
Transplanting: when, into what, and avoiding transplant shock
Transplant when roots fill the current container but before they circle: typically seedling plug to 1–3 L at 2–3 weeks, then to the final pot 2–4 weeks before flowering. Move the root ball intact into pre-moistened medium at the same pH and similar EC, water in lightly, and keep light and climate gentle for a few days. Autoflowers do best sown straight into their final pot.
Environment
Temperature, humidity, VPD, airflow, CO₂ and light
Airflow: air exchange, canopy air speed and fan placement
Aim for gentle, constant movement across and under the canopy (roughly 0.3–1.0 m/s at leaf level) plus enough exhaust to remove heat and humidity, typically one full tent air exchange every 1–3 minutes for a lit tent. Moving air thins the leaf boundary layer, which raised canopy photosynthesis in non-cannabis research, and dries out the microclimates where mould starts.
CO₂ enrichment: when it pays, how much, and how to stay safe
Raising CO₂ from ambient (~420 ppm) to 800–1,200 ppm during lights-on raises cannabis photosynthesis substantially, but only pays when light is already high (roughly 900+ µmol/m²/s) and the room is sealed enough to hold it. Keep occupied rooms below the 5,000 ppm 8-hour workplace limit and never enter a room above 30,000 ppm.
Heat and light stress: taco leaves, bleaching and foxtails
Heat and light stress show at the top of the plant, closest to the light: leaves curl up or taco, bracts bleach white or yellow, buds may foxtail. Measure leaf temperature and canopy PPFD before blaming nutrients. Typical fixes: dim or raise the light 10–20 %, bring leaf temperature under about 30 °C (86 °F), restore airflow and root-zone water uptake.
Humidity by stage: RH targets from clone to cure
Run about 65–80 % RH for clones and seedlings, 55–70 % in veg, 50–60 % early flower and 40–50 % in late flower, adjusted to hit a leaf VPD band at your temperature. High RH in flower raises bud-rot and mildew risk and, in a 2025 study, delayed flowering and lowered cannabinoids. Dry and cure near 60 % RH.
Light spectrum: blue, red, far-red and UV, what's real
Photon quantity (PPFD/DLI) and fixture efficacy matter far more than spectrum. Less blue slightly increased cannabis yield (about 12 % from 4 % to 20 % blue). Far-red stretches plants; its yield effect is contested and seems to trade off against cannabinoid concentration. UV has repeatedly failed to raise cannabinoids in controlled trials and can cut yield at high doses.
Photoperiod and light leaks: 18/6, 12/12 and the dark period
Photoperiod cannabis stays vegetative under long days (18/6 up to 24/0; no sleep period is needed in veg) and flowers when the uninterrupted night is long enough: 12/12 or 13/11, and some cultivars flower at 14–15 h, usually as ~12 h at high intensity plus sunrise and sunset ramps. Light during the dark period, even very dim, can delay or weaken flowering in sensitive cultivars; leaks can also expose herm-prone genetics, triggering male flowers on susceptible plants. Some cultivars yield more at 13–14 h days, at a possible cost in THC concentration.
Nutrients
Every element, deficiencies and toxicities, feed schedules, recipes
"Bloom boosters" for cannabis: what's real and what's marketing
Most bloom boosters are concentrated phosphorus and potassium. Four independent controlled cannabis trials found no increase in flower yield or cannabinoids from raising phosphorus above roughly 25–60 mg/L, and one found no yield response to potassium anywhere from 60 to 340 mg/L. A complete, balanced flower feed is what matters; extra P and K mostly end up in the runoff and can induce magnesium, calcium, zinc and iron problems. Some boosters have been reported to contain undeclared plant growth regulators, which have no place in a consumable crop.
Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window
Boron cross-links cell-wall pectin and is needed wherever cells are dividing: shoot tips, root tips and flowers. Deficiency in cannabis causes stunted, distorted new growth, dead growing tips and wilting from root-tip death; toxicity scorches the margins of older leaves. Supply about 0.2–0.5 mg/L B; cannabis tolerated a tenfold dose for weeks but the gap between enough and too much is narrower than for most nutrients.
Building a cannabis feed by stage: ppm targets per element and how to hit them
A good mineral cannabis feed runs roughly N 150–200, P 30–60, K 175–250, Ca 150–200, Mg 40–70 and S 60–120 mg/L in veg and flower, plus Fe 1.5–3 and small amounts of Mn, Zn, B, Cu and Mo, at an EC of about 1.2–1.8 mS/cm in veg and 1.6–2.2 in flower. Cannabis research shows no benefit from pushing P or overall strength higher. This article gives the targets, the evidence behind each, and two worked RO-water recipes with a sources table.
Cal-Mag: what it is, when you need it and when you don't
Cal-Mag is a calcium and magnesium supplement, usually calcium nitrate and magnesium nitrate, sometimes with iron. You need it when your water and base nutrient together supply too little Ca and Mg: RO or very soft water, new or unbuffered coco, or a base nutrient designed for hard water. How much a plant needs is driven mainly by its cultivar, the water source, the medium (coco's cation exchange), root-zone pH and transpiration. The claim that LED lights create a Cal-Mag need is a myth. You do not need it on hard tap water with a complete base feed, and overusing it adds nitrogen and pushes potassium and magnesium out of balance.
Calcium (Ca) in cannabis: deficiency, transport, targets and sources
Calcium builds cell walls and membranes and moves only in the transpiration stream, so it cannot be moved from old leaves to new ones. Feed about 150–200 mg/L Ca in soilless systems, and remember that most 'calcium deficiency' is a delivery problem (low transpiration, high humidity, root damage, competing K/Mg/NH4) rather than an empty bottle. Classic signs are distorted, stunted new growth and brown spots.
Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add
Chloride (Cl-) is an essential micronutrient for water splitting, osmotic balance and stomata, but the requirement is tiny and always met by water and fertiliser impurities. In practice chloride is a salinity problem, not a deficiency: keep it below roughly 50–70 mg/L in the feed, watch it in coco and some tap waters, and don't confuse chloride (a nutrient ion) with chlorine or chloramine (disinfectants).
pH and EC
pH, EC and ppm scales, water quality, runoff, drift
Buffering coco coir: why it matters and how to do it
Coco coir has a high cation exchange capacity that arrives loaded with potassium and sodium. Unbuffered, it grabs calcium and magnesium from your feed and releases K and Na, causing early Ca/Mg deficiency. Buffering means soaking washed coco in a calcium (and usually magnesium) nitrate solution so the exchange sites are filled with Ca and Mg before planting, then rinsing. It is standard grower and industry practice with sound chemistry behind it, though controlled studies on cannabis are lacking.
EC vs PPM: the 500 and 700 scales, CF, and how to convert
EC (electrical conductivity, in mS/cm) is what every meter actually measures. 'PPM' or TDS readings are EC multiplied by an assumed factor: 0.5 on the 500 (NaCl) scale, 0.7 on the 700 (442 or KCl-style) scale, sometimes 0.64. So 1.0 mS/cm reads 500 ppm on one meter and 700 ppm on another. Always talk in EC, or state the scale. Feed charts quoting ppm without a scale are ambiguous by 40%.
pH and EC meter calibration: buffers, slope, storage and when to replace a probe
Calibrate pH meters with at least two fresh buffers that bracket your readings (pH 7 then pH 4 for growing), before any session where decisions matter and at least weekly. Store glass pH probes wet in storage solution or pH 4/7 buffer, never in RO water or dry. Check EC meters against a 1.413 mS/cm standard. A pH probe with a slope below about 90-95% or one that can no longer be adjusted to buffer should be replaced; typical glass electrodes last one to two years.
pH and nutrient availability: what pH really controls, by medium
pH controls how soluble each nutrient is and how well roots absorb it. The accepted ranges are soil about 6.0–7.0 and soilless/hydro about 5.5–6.5 (sweet spots: 5.5–6.2 in hydro, 5.8–6.3 in coco and rockwool, 6.2–6.8 in soil), and drift within the range is normal. High pH starves plants of iron, manganese, zinc, boron and phosphorus; low pH makes iron and manganese overly available and reduces calcium, magnesium and molybdenum. The classic availability bar chart was built for mineral soils and overstates the effect in chelated soilless feeds. The ranges are broadly agreed accepted practice, from extension and grower consensus.
pH drift in hydro: why reservoir pH rises (and sometimes falls)
Reservoir pH usually rises because plants absorb nitrate and release hydroxide or bicarbonate to stay electrically balanced; aeration driving off CO2, alkaline top-up water and algae add to it. Ammonium does the opposite. A steady upward drift of a few tenths per day in a healthy, growing system is normal. Manage it with a small ammonium share (5–15% of N), acidifying alkaline water, and letting pH ride within 5.5–6.2 rather than chasing a single number. A fast unexplained fall, or a rise with brown roots, points to root or microbial trouble.
Runoff testing: how to measure root-zone pH and EC and what the numbers mean
Runoff (leachate) pH and EC tell you what the roots are actually sitting in, which is often different from what you fed. Use the pour-through method: water to full saturation, wait 30 minutes to 2 hours, then pour a measured amount of water on top and collect about 50 mL. Compare runoff EC with input EC: higher means salts are building up, much lower means the plant is hungry or you are over-leaching. Track the trend over weeks rather than reacting to one reading.
Systems
Soil, coco, rockwool, living soil and every hydro system
Bottom-watering, soak trays and wick (self-watering) systems
Bottom-watering lets pots draw solution up from a tray, either by a timed soak (flood 2–5 cm for 10–30 minutes, then drain) or by a constant shallow level held by a float valve or wick. It is gentle and labour-saving and suits soil, but salts accumulate at the top of the pot, so feed at lower EC than top-feeding and top-water to runoff every week or two.
Choosing your growing system: soil, coco, rockwool or hydro
Choose by how much attention and measurement you can give, not by yield claims. Soil and living soil forgive mistakes for days; coco and drip need daily feeding; DWC, NFT and aeroponics grow fast but can lose roots within hours if a pump or air supply fails. No controlled study shows one system out-yielding the others when light and climate are equal.
Deep water culture (DWC)
In DWC roots hang in an aerated nutrient solution. It grows fast but depends on two things: dissolved oxygen (keep above about 6 mg/L, ideally near saturation) and solution temperature (18–22 °C / 64–72 °F). Warm, poorly aerated water is how Pythium root rot starts. Run pH 5.6–6.0 and EC 0.8–2.0 mS/cm by stage, and treat the air pump as life support.
Drain-to-waste drip and crop steering (generative vs vegetative dryback)
Drain-to-waste drip sends fresh solution every shot and discards runoff, so you control the root zone by irrigation timing, shot size and substrate EC measured with a VWC/EC probe. Vegetative steering uses earlier first shots, larger shots and small overnight drybacks (about 10–15 % VWC); generative steering delays the first shot, uses smaller shots, longer P3 and larger drybacks (about 20–35 %) with higher substrate EC. The ranges are grower practice; one cannabis study found controlled late-flower drought raised cannabinoid concentration.
Ebb and flow (flood and drain)
A pump floods a table or tray of pots to a standpipe height, then the solution drains back to the reservoir. Each flood refreshes water and pulls fresh air into the medium as it drains. Typical schedules: clay pebbles 3–6 floods per light period of 10–15 minutes, coco or rockwool 1–3. It is robust because the media buffer pump failures for days, but salts can build up at the top of the medium.
Fogponics: ultrasonic fog for roots (a supplement, not a system)
Fogponics uses ultrasonic transducers to make a 5–10 µm water fog that is blown into a root chamber. Fog carries very little dissolved nutrient (salts stay behind and concentrate in the fogger tank), transducers wear out in roughly 1,000–3,000 hours and run hot, so GenetixBay treats fog as a humidity supplement for cloning domes and aeroponic chambers, not as a standalone way to feed a flowering plant.
Training
Topping, LST, SCROG, SOG, mainlining, defoliation
Defoliation and lollipopping: what to remove, when, and the evidence
Lollipopping strips small branches and leaves from the shaded lower third at or near the flip; defoliation removes fan leaves that shade bud sites or block airflow. In a controlled study on large plants, neither defoliation three weeks before harvest nor lower-branch removal changed flower or cannabinoid yield per plant, and defoliation improved cannabinoid uniformity. Stripping within reason doesn't hurt yield, but in the founder's experience tucking helps more: tuck and train first. Whether tucking beats stripping, and whether defoliation raises cannabinoids, is an open GenetixBay trial question.
FIM: pinching most of the tip for multiple tops
FIM removes roughly 70–80 % of the newest growth at the tip instead of cutting cleanly above a node. When it works, three to five shoots grow from the same point; when it doesn't, you get one or two, like a sloppy top. It is less predictable than topping and has no controlled research behind its yield claims.
HST and supercropping: controlled stem crushing
Supercropping pinches and gently crushes a green stem until the inner tissue softens, then bends it over so the tip sits lower. It is used to tame tall shoots in late veg and early stretch. Done right the stem forms a firm knuckle in a few days. Stem snapping gives better buds in the founder's long experience: *Grower practice*, house-endorsed, though no controlled study has measured a potency gain yet. Every cultivar responds differently.
LST: low-stress training
Low-stress training bends and ties stems outward and down so the plant grows as a flat, even canopy, without cutting anything. It is the safest training method, suits autoflowers, and works with topping and SCROG. Start in early veg, adjust ties every few days, and stop bending hard once stems lignify in mid-stretch.
Mainlining and manifolding: building a symmetrical plant
Mainlining (manifolding) tops a young plant down to the third node, removes all lower growth, and then tops each arm repeatedly to build a symmetrical hub feeding 8 or 16 evenly matched colas. It produces a very even canopy at the cost of 2–4 extra weeks of veg. It is grower practice with no controlled studies; the closest research found double pruning increased yield per plant.
SCROG: screen of green
SCROG uses a horizontal net 20–40 cm above the pots to spread a few plants into a flat, even canopy: shoots are tucked under the net through veg and early stretch, then allowed to grow up through it. It suits small rooms and plant-count limits, at the cost of longer veg. Fill about 70–80 % of the net before flipping, since plants stretch to fill the rest.
Pests
Identification, life cycles, thresholds and IPM
Aphids on cannabis: cannabis aphid, green peach aphid and friends
Aphids are soft-bodied sap feeders that cluster on leaf undersides and stems, shed white skins and drip sticky honeydew; they breed asexually and fast, so catch them early and use parasitoid wasps, predatory midges and lacewings, with soaps or oils only before flower.
Broad mites and hemp russet mites: the invisible ones
Broad mites (Polyphagotarsonemus latus) twist and harden new growth; hemp russet mites (Aculops cannabicola) bronze leaves and curl edges upward. Both are too small to see without 20x or more, are mistaken for nutrient problems, and are managed by clean stock, quarantine, preventive predatory mites and removal of infested plants.
Caterpillars and budworms on cannabis
Caterpillars, mainly corn earworm (Helicoverpa zea) outdoors, bore into buds, leave frass and start bud rot; scout from early flower, use pheromone traps for moth flights, exclude moths with netting, and use Bt (kurstaki or aizawai) while larvae are small, since it must be eaten and breaks down in sunlight within days.
Fungus gnats: the watering problem with wings
Fungus gnats (Bradysia spp.) breed in constantly wet, organic-rich media; adults are a nuisance but larvae chew roots of seedlings and clones and can open the door to Pythium and Fusarium. Fix the watering first, then use Bti, Steinernema feltiae nematodes or soil predatory mites, and sticky cards to monitor.
Root aphids (rice root aphid) on indoor cannabis
The 'root aphid' of indoor cannabis in North America is mainly the rice root aphid (Rhopalosiphum rufiabdominale); wingless colonies feed on roots and cause slow growth, wilting and yellowing that look like nutrient or watering problems. Confirm by inspecting roots and cards, then rely on sanitation, a plant-free gap between cycles, and soil-applied biologicals.
Spider mites on cannabis: ID, lifecycle and IPM
Twospotted spider mites (Tetranychus urticae) cause pale stippling on leaf tops and webbing at heavy populations; they breed fastest in hot, dry rooms, so control rests on early scouting, cooler and more humid conditions, and predatory mites released before numbers explode, with soaps or oils only before flower.
Diseases
Mildew, botrytis, root rot, viruses and viroids, sanitation
Botrytis (bud rot / grey mould) in cannabis
Bud rot is Botrytis cinerea rotting dense colas from the inside, favoured by cool-to-moderate temperatures (10–27 °C, optimum near 20 °C), high humidity and free water on tissue. There is no cure in flower: prevent it with RH below about 50 % in late flower, dew-point control at lights-off, airflow, open canopies and fast removal of infected buds.
Fusarium in cannabis: wilt, crown rot and bud rot
Fusarium fungi cause three different problems in cannabis: vascular wilt (F. oxysporum), root and crown rot (mainly F. solani), and a pinkish-white bud rot. There is no cure once a plant is infected; remove it, stop root-zone stress, sanitise pots and water, and source clean clones and media.
Hop latent viroid (HLVd, 'dudding') and other cannabis viruses
Hop latent viroid is a tiny infectious RNA that spreads through sap on tools, hands, clones, recirculating water and seed, and causes 'dudding': stunting, brittle stems and small, low-resin flowers. There is no cure in a plant. Test mothers (roots and leaves) by RT-PCR/RT-qPCR, discard positives, disinfect tools with bleach or heat (not alcohol), and use meristem tissue culture to rescue valuable genetics.
Powdery mildew in cannabis
Powdery mildew is a leaf-surface fungus (mainly Golovinomyces ambrosiae) that thrives in still, humid, moderate-temperature canopies and spreads by airborne spores. Prevent it with airflow, stable humidity, clean clones and resistant genetics; treat early in veg with least-toxic contact options, because once it reaches flowers there is no clean fix.
Root rot and Pythium in cannabis
Pythium root rot is a water mould that thrives in warm, low-oxygen root zones and swims between plants in recirculating water. Brown, slimy roots whose outer layer slides off, plus wilting with a wet root zone, are the signature. Fix the root-zone conditions first: solution at about 18–21 °C (65–70 °F), high dissolved oxygen, clean water and no overwatering; then remove dead roots and re-establish beneficial microbes.
Sanitation and disease prevention for cannabis grows
Most cannabis disease problems are brought in on clones, tools, hands, media or water, and then helped along by humid, stagnant rooms. Quarantine and test incoming plants, work clean-to-dirty, clean then disinfect with the right chemical class for the pathogen (bleach or hypochlorous acid or heat for viroids; alcohol and peroxide do not inactivate HLVd), treat recirculating water, and keep the climate out of the disease zone.
Diagnosis
Symptom-led decision trees: start here when something looks wrong
Brown or burnt leaf tips on cannabis: a differential
Crispy brown tips on otherwise healthy leaves usually mean too much salt in the root zone (EC too high, or salts building up because of low runoff or drying out), not a deficiency. Check runoff or reservoir EC against input first, then watering rhythm, then heat and low humidity, and only then K or B disorders.
Brown roots in hydroponics (DWC, RDWC, NFT): a differential
Healthy hydro roots are white to cream and firm. Brown roots that are still firm and odourless are often just stained by nutrients or additives; brown, slimy, smelly roots whose outer layer slips off are root rot, usually Pythium, favoured by warm, oxygen-poor solution. Check solution temperature and dissolved oxygen first, then root texture and smell.
Clawing leaves on cannabis: a differential
Leaves that curl down at the tips like a talon, especially if dark green and glossy, most often mean excess nitrogen and high EC, or a waterlogged, oxygen-starved root zone. Check watering and runoff EC first; distorted, crinkled clawing on new growth instead points to broad mites, calcium/boron problems or a viroid.
Drooping cannabis: overwatering vs underwatering
Lift the pot: a heavy pot with firm, swollen-looking drooping leaves is overwatered (roots short of oxygen); a light pot with limp, papery leaves is underwatered. If the medium is moist and the plant still wilts, especially one plant at a time or in hydro, suspect root rot or vascular wilt and look at the roots.
Foxtailing buds on cannabis: genetics or stress?
Foxtails (new calyx spires growing out of mature buds) are either a cultivar trait, which appears evenly through the canopy, or a stress response to heat and intense light, which shows mostly on the top colas nearest the fixture. Measure canopy leaf temperature and PPFD at the tops; evidence is mainly grower observation.
Hermaphrodite cannabis (bananas and nanners): what to do
Hermaphroditic flowers are anthers (often banana-shaped) or pollen sacs forming on a female plant. Cannabis is a dioecious species, and a well-bred female should stay female; herm-prone plants are mainly the product of bad breeding (repeated selfing, careless feminising, untested 'pollen chucker' seed). Stress such as light leaks or heat reveals that weakness rather than causing it in sound genetics. Fix the environment, remove the plant if it sheds pollen, and never keep it as a mother or breed from it.
Harvest and cure
Ripeness, flushing evidence, drying, curing, storage
Curing and burping: jars, humidity and how long
Curing is a slow, steady decline in the bud's moisture content and water activity, not a constant hold: start around aw 0.62–0.65 and let it settle towards 0.55–0.58 over two to eight weeks, burping daily at first, then weekly. Jar RH is only a proxy for the bud, valid once a sealed jar has equilibrated (aw ≈ RH / 100). Check with the stem snap, an equilibrated hygrometer and weight. Humidity packs are a marketing gimmick; if a jar is too dry, add a fresh bud.
Drying cannabis: the 60/60 method and water activity
Dry slowly and in the dark at about 15–21 °C (60–70 °F) and 55–62 % RH, the popular 60/60 target, for 7–14 days until small stems snap and buds reach a water activity of about 0.60–0.65. ASTM D8197 sets 0.55–0.65 aw as the range that protects against mould without making flower brittle. Judge the bud (stem snap, an equilibrated jar reading, weight), not the room. Wet vs dry trim is grower preference. Fast, warm drying loses volatile monoterpenes, and wet, still air grows mould.
Long-term storage: keeping cured flower potent and aromatic
Light is the biggest single cause of cannabinoid loss in storage, air oxidation turns THC into CBN, and warmth and humidity speed both and invite mould. Store cured flower in full, airtight, opaque glass with the bud at aw 0.55–0.65 (an equilibrated jar reading), cool and dark; skip humidity packs, a marketing gimmick. Kept that way it is reasonably stable for one to two years; at room temperature over several years THC loss can be near total. Freezing is possible but makes trichomes brittle.
Pre-harvest flushing: a myth that costs you yield and resin
Pre-harvest flushing is a myth, and a harmful one. Starving the plant of nutrients in its last weeks takes food away during the phase when it is packing on most of its final weight, trichomes and resin, so it costs yield and resin and gives nothing back: controlled studies found no gain in flower quality, minerals or cannabinoids, and longer nutrient withdrawal tended to cut dry mass and cannabinoid yield. Cannabis stores what it takes up in its tissue, and plain water at the end does not wash it out. Feed through to harvest at stage-appropriate strength; taste and ash are made by plant health, not overfeeding, and slow drying and proper curing. The one valid flush treats the medium, not the plant: a root-zone flush to wash out accumulated salts, at any stage.
Trichome ripeness: clear, cloudy, amber, and what the evidence says
Trichome heads go from clear to cloudy (milky) to amber or brown as flowers mature; research confirms browning marks gland senescence and that trichomes on one bract mature unevenly and at genotype-specific rates. Cannabinoid concentration typically rises to a plateau and then falls as plants senesce. The popular claim that amber heads mean high CBN and couch-lock is a myth: CBN mainly forms by oxidation after harvest. A dark period before harvest is a myth too. Harvest when most heads are cloudy with some amber, and track it by date and lab tests for your cultivar.
Breeding
Genetics, pollination, selection, stabilisation, seed production
Backcrossing, IBLs and stabilisation
A backcross crosses offspring back to one parent (the recurrent parent) to recover that parent's genome while keeping a trait from the other: each backcross halves the donor's share (50%, 25%, 12.5%, 6.25%...). An IBL is a line inbred and selected over many generations until it breeds fairly true. 'Stable' should mean measured uniformity across a grow-out, not a generation count.
Breeder record-keeping and naming ethics
Keep a dated record of every plant, cross, batch and test, linked by permanent IDs, so any seed can be traced to its parents. Name lines honestly: a new, unique name for new genetics, the original name only for the original genetics, clear labels (F2, BX, S1, feminised), and never a famous name on something it isn't. Names are claims; records are the evidence. Sex stability is part of the ethics: cull herm-prone plants, never breed from them, and publish every batch's herm rate.
Breeding autoflowers: getting the trait into a photoperiod line
Because autoflowering is recessive in mapped populations, a photo x auto F1 is all photoperiod. You recover autos in the F2 (about 1 in 4) or by backcrossing the F1 to the auto parent (about 1 in 2). To make an auto version of a photoperiod line, alternate crossing to the photo parent with a generation that reveals autos, or use a DNA marker to keep carriers.
Chemotype inheritance: how THC and CBD synthase alleles pass on
Whether a plant is THC dominant, CBD dominant or mixed is controlled mainly by a single inheritance block carrying THCA synthase and CBDA synthase genes, which behaves close to codominant: THC x CBD gives mixed (type II) F1s and a 1:2:1 split in the F2. CBG-dominant and cannabinoid-free types come from non-functional synthase alleles. Total cannabinoid amount is a separate, quantitative trait.
Clone-only cuts and how to preserve them
A clone-only is one selected genotype kept alive by cuttings. It can be lost to pests, disease, hop latent viroid (HLVd) or accident, and it accumulates rare somatic mutations, which are not the same thing as a loss. Cuts from different parts of a plant can also behave differently (topophysis), so take them from consistent locations. Preserve it with clean, tested mothers in at least two locations, regular fresh cuttings, a tissue-culture backup where possible, and seed (S1s or crosses) as genetic insurance, not as a copy.
Collecting and storing cannabis pollen
Collect pollen from freshly opened sacs in still, clean air, sieve it, dry it briefly, and use it within days, or mix it with a dry carrier (baked flour), seal it with desiccant and freeze it. Cannabis pollen loses viability within about a week in a fridge; one study kept it viable for at least four months by mixing it 1:10 with baked flour, vacuum-drying and storing in liquid nitrogen. Home freezer storage is grower practice and should be germination tested.
Genetics history
Landraces, heritage lines and lineages, with evidence labels
How hybrid 'strains' emerged
Modern drug-type cannabis is mostly a mix of South Asian-derived long-flowering types and Central Asian (Afghan) hashish types, crossed from the 1970s onwards in North America, then distributed by Dutch seed companies from the mid-1980s, and multiplied into thousands of names in clone-driven and legal markets since the 1990s. The broad story is supported by genetics; most specific pedigrees are oral claims with conflicting versions.
Indica, sativa and ruderalis: what the names really mean
Cannabis is one species, Cannabis sativa L., showing different phenotypes. Nearly everything grown today is a hybrid, with a few outlier landraces. Distinct groups, ruderalis included, may have existed long ago, but not today. As a guide to effects or species, indica vs sativa is nonsense: genetic and chemical studies show the labels don't match ancestry or predict chemistry. At most they describe plant shape: leaflet width, structure and flowering time.
Landraces of the world: an overview
Drug-type cannabis landraces developed across South and Central Asia and were carried to Africa, the Middle East and the Americas, where local farmers adapted them over centuries. Genomic work points to an Asian origin of domestication (exact region contested). Many traditional landraces are now endangered by hybrid replacement, and most 'landrace' seed in commerce is better described as heirloom: collected at some point, then maintained elsewhere. Every origin story here is a claim; this article labels the evidence.
Old cannabis wasn't weak: the "so much stronger than 20 years ago" myth
"Cannabis is far stronger than it used to be" is false as a claim about the plant's genetics. Famous hashish, charas and sinsemilla traditions are centuries old and impossible with 5 % plants, and old seed grown well today still tests high. The 'weak old weed' numbers come from seized samples: mostly cheap compressed export brick of leaf, seed and stem, often stored for years before testing, measured with changing methods. The best of what source regions grew was rarely exported. What changed is the market and growing technique: fresh, seedless, indoor flower.
Patents and the gene pool: who can own a cannabis plant?
Cannabis can be protected by US utility patents (covering plants, traits, extracts and methods), plant patents (for asexually reproduced varieties) and plant variety protection certificates (for seed-propagated hemp, since 2019), plus plant breeders' rights in Canada and the EU. Grants are public record. Legal commentators worry that thin prior art and broad claims could fence off parts of a shared gene pool. The open responses are public, dated documentation: prior-art databases, open-source seed pledges and genotype registries. GenetixBay's answer is preservation, GB-ID documentation and open sharing.
Why everything tastes the same: the evidence that commercial cannabis is converging
Growers keep saying modern weed all tastes the same, and the data back them up. A study of nearly 90,000 US lab results found THC-dominant flower falling into just three terpene groups, two of which held about 87 % of samples. Strain names and indica/sativa labels promise far more variety than the chemistry shows, traditional landraces in their home regions are being replaced by introduced hybrids, and retail prices rise with THC rather than aroma. GenetixBay's answer is preservation, documentation with GB-IDs, and open sharing of distinctive lines.
