# Soil first grow, week by week

> A soil first grow is the most forgiving: a quality bagged potting mix with 20–35 % perlite in an 11–19 L (3–5 gal) pot, water at pH 6.2–6.8 when the pot feels light, plain water for the first 2–4 weeks while the mix's starter charge lasts, then a dilute feed at EC 0.8–1.6 mS/cm rising through flower. A photoperiod plant runs about 17–20 weeks seed to harvest: 3 weeks seedling, 3–5 weeks veg, a 10–14 day transition and 7–10 weeks of flower.

- Canonical: https://genetixbay.com/knowledge/guides/soil-first-grow-week-by-week.html
- Category: Start here · Level: Beginner
- Evidence: Grower practice · Status: Draft: awaiting expert review
- Stage: Seedling, Veg, Transition, Flower, Ripening, Harvest · Systems: Soil
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**What soil should I use for a first cannabis grow?** Use a quality bagged [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) (peat or coco with compost) and add 20–35 % [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) or pumice for air, not garden soil, which compacts and carries pathogens. A light 'seedling' or lightly amended mix is safer than a 'hot' heavily fertilised one for young plants. Fill 11–19 L (3–5 gal) pots with [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) holes and pre-moisten the mix before planting.

**When should I start feeding plants in soil?** In most bagged potting mixes, start feeding at about week 3–5 from sprout, when the mix's starter fertiliser runs out and the lower leaves begin to lighten. Begin at a quarter to half label strength, around [EC](https://genetixbay.com/knowledge/glossary/ec.md) 0.8–1.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), every second or third watering, and raise it as the plant grows. Heavily amended organic mixes may need water only for 4–6 weeks or longer.

**How often do I water cannabis in soil?** Water cannabis in soil when the pot feels light and the top 2–3 cm (1 in) is dry, typically every 2–4 days in veg and every 1–3 days in late flower in an 11–19 L (3–5 gal) pot. Water slowly until about 10 % runs out of the bottom, then empty the saucer. Never water on a fixed schedule; lift the pot instead.

**What [pH](https://genetixbay.com/knowledge/glossary/ph.md) should water be for soil?** Water and feed for soil-grown cannabis should be at about pH 6.2–6.8, within the broadly agreed soil range of 6.0–7.0. Peat-based mixes buffer pH, so a reading drifting by a few tenths within that range is normal. Check runoff pH every week or two; if runoff sits below 5.8 or above 7.2, adjust your input pH by 0.2–0.3 for the next few waterings.

**Should I [flush](https://genetixbay.com/knowledge/glossary/flushing.md) my soil plants before harvest?** No. Pre-harvest flushing is a myth that starves the plant while it packs on its final weight and resin. Keep feeding soil plants at the strength the stage needs right up to harvest. If you see [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) (runoff EC well above input, burnt tips), a root-zone flush to clean the medium is valid at any stage; it treats the soil, not the plant.

**How long does a soil grow take week by week?** A soil [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) grow takes about 17–20 weeks from seed to harvest: about 3 weeks of seedling, 3–5 weeks of veg, a 10–14 day transition after the [flip to 12/12](https://genetixbay.com/knowledge/glossary/12-12.md), then 7–10 weeks of flower counted from the first pistil clusters. Add 1–2 weeks of drying and 2–8 weeks of curing. An autoflower in soil finishes in about 9–14 weeks from seed.

**Short answer.** Soil is the most forgiving first grow. Use a quality **bagged potting mix with 20–35 % perlite** in an **11–19 L (3–5 gal)** pot. Water at **pH 6.2–6.8** when the pot feels light, to about 10 % runoff. Give **plain water for the first 2–4 weeks** while the mix's starter charge lasts, then a dilute feed at **EC 0.8–1.6 mS/cm**, rising through flower and fed right to harvest. A photoperiod plant takes about **17–20 weeks** from seed to harvest.

This guide follows one feminised photoperiod plant. For autoflowers in soil, follow the [autoflower guide](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md); the mix and watering are the same, but there is no flip and no transplant. The why behind each step is in [soil as a growing system](https://genetixbay.com/knowledge/systems/soil.md).

## What do you need for a soil grow?

A soil grow needs the basic tent kit ([choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md)) plus:

- [ ] Quality bagged [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), lightly amended (not a "hot" mix for seedlings), about 15–20 L (4–5 gal) per plant
- [ ] [Perlite](https://genetixbay.com/knowledge/glossary/perlite.md) or pumice, 20–35 % by volume if the mix isn't already airy
- [ ] One 11–19 L (3–5 gal) final pot per plant with drainage, plus a 0.5–1 L (pint–quart) starter pot or cup if you are not sowing straight into the final pot
- [ ] Saucers or a tray to catch runoff
- [ ] A soil-suitable base nutrient (bottled mineral or organic, one-part or two-part)
- [ ] pH pen with pH 4 and 7 buffers, pH up and down ([pH made simple](https://genetixbay.com/knowledge/guides/ph-made-simple.md))
- [ ] EC meter ([EC and ppm scales](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md))
- [ ] A watering can or jug with volume marks, and a measuring syringe
- [ ] A kitchen or luggage scale for weighing pots (optional but excellent)
- [ ] Yellow [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) for [fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md)

## What does a soil grow look like, week by week?

A soil grow moves from plain water to a gently rising feed, with watering volume growing as roots fill the pot. Weeks count from the seedling breaking the surface.

| Week | Stage | Light (µmol/m²/s, hours) | Water per 11–19 L pot | Feed EC (mS/cm) | Key jobs |
|---|---|---|---|---|---|
| 1 | Seedling | 150–250, [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) | 50–100 mL ring around the stem every 1–3 days | Water only, pH 6.2–6.8 | Keep the top moist, not wet |
| 2 | Seedling | 200–300, 18/6 | 100–250 mL | Water only | Second and third sets of [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) |
| 3 | Early veg | 300–400, 18/6 | 0.25–0.5 L | Water only in most mixes | Pot up from a cup into the final pot if needed |
| 4 | Veg | 350–450 | 0.5–1 L | 0.8–1.0 if lower leaves pale | Start [LST](https://genetixbay.com/knowledge/guides/training-basics.md) |
| 5 | Veg | 400–500 | 1–2 L | 1.0–1.2 | Top once if you want (photoperiods only) |
| 6–7 | Late veg | 450–600 | 1.5–3 L | 1.2–1.4 | Fill the canopy; flip at half the final height you can fit |
| 8–9 | **Transition** (days 1–14 after the flip) | 600–700, 12/12 | 2–3 L | 1.2–1.4 | Stretch; tie down; check for male flowers |
| 10–12 | Early flower | 700–900, 12/12 | 2–4 L | 1.4–1.6 | Lower RH to 45–55 %; tuck leaves, don't strip |
| 13–15 | Mid flower | 700–900 | 3–5 L, may need water every 1–2 days | 1.4–1.8 | Weekly pest check; support colas |
| 16–18 | Late flower and ripening | 700–900 | 3–5 L | 1.2–1.6, taper only N if you mix salts | RH 40–50 %; check [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) from week 15 |
| 17–20 | Harvest | | | Feed to the end; **no flush** | Harvest by trichomes, then dry |

Water volumes assume an [LED](https://genetixbay.com/knowledge/glossary/led.md) tent at the climate targets; heat and big plants drink more. The 10–14 day transition after the flip is real: the first pistil clusters appeared about 13–14 days after short days on average in a 27-cultivar study [5]. Count both days since flip and days of flower ([grow calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md)).

## How do you run a soil grow, step by step?

Run a soil grow in these steps; each one has a sibling guide for detail.

1. **Mix and fill.** Blend the potting mix with 20–35 % perlite if it feels dense. Fill the pot to 2–3 cm (1 in) below the rim. Never use garden soil in pots: it compacts and carries damping-off pathogens [1][3].
2. **Pre-moisten.** Water the filled pot with pH 6.2–6.8 water until it drips, then let it drain for a day. Weigh it: that's your "wet" weight.
3. **Plant.** Sow a cracked seed root-down 0.5–1 cm (¼–½ in) deep ([germinating seeds](https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.md)), either straight into the final pot or into a 0.5–1 L cup.
4. **Water the seedling in a ring.** 50–100 mL around the stem, every 1–3 days, only when the top 1 cm (½ in) is drying. In a big pot of wet mix, the seedling may need no water for several days.
5. **Pot up (photoperiods only, if you started in a cup).** At 2–3 weeks, when roots reach the cup's sides, move the intact root ball into the pre-moistened final pot at the same depth ([transplanting](https://genetixbay.com/knowledge/germination/transplanting.md)). Autoflowers should start in the final pot.
6. **Water by weight from week 3.** Lift the pot. When it feels clearly lighter than wet (often about 40–50 % of the water gone), water slowly until about 10 % drains out, then empty the saucer within 30 minutes ([watering](https://genetixbay.com/knowledge/guides/watering-how-much-how-often.md)).
7. **Start feeding when the mix runs out.** Usually week 3–5: the lowest leaves lighten evenly. Begin at a quarter to half label strength (EC about 0.8–1.0 mS/cm including your water), every second or third watering at first [2].
8. **Raise the feed gradually.** Increase by about 0.2 mS/cm a week if the plant stays deep green with no burnt tips. More is not better: pushing nutrient strength higher gave no yield or [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) benefit in a controlled study [8] ([feeding basics](https://genetixbay.com/knowledge/guides/feeding-basics.md)).
9. **Train in veg.** Bend and tie the main stem from week 4; tuck leaves to open bud sites rather than pluck them ([training basics](https://genetixbay.com/knowledge/guides/training-basics.md)).
10. **Flip to 12/12.** When plants are about half the final height you can fit (often week 6–7), switch the timer and log the date. Expect the stretch and the 10–14 day transition.
11. **Check runoff every 1–2 weeks.** Collect runoff and read pH and EC ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). Runoff EC much higher than input means salt build-up; much lower means the plant is hungry.
12. **Feed through to harvest.** Keep stage-strength feeding. If you mix single salts, taper only nitrogen over the last 2–3 weeks while keeping P, K, Ca, Mg, S and micros fed [6]. Do not flush (below).
13. **Harvest by trichomes** ([when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md)), then [dry](https://genetixbay.com/knowledge/guides/drying-step-by-step.md) and [cure](https://genetixbay.com/knowledge/guides/curing-step-by-step.md).

## Do you need to flush soil plants before harvest?

No. Pre-harvest flushing is a *Myth*, and in soil it is actively harmful: it starves the plant in its last weeks, when it is packing on most of its final weight, trichomes and resin. A controlled study of flushing found no quality benefit [7]; see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). Lower nitrogen late can raise cannabinoid percentage while lowering total yield, a trade-off made through the feed, not by withholding everything [6].

The one valid flush is a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) to wash [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) out of the mix: water with about 2–3 times the pot volume of pH-adjusted water, then resume a normal feed at the next watering. It treats the soil, not the plant, and can be done at any stage.

## Is bigger always better for soil pots?

Bigger pots give bigger plants within reason and hold water for longer, so 11–19 L (3–5 gal) forgives a missed day [4]. Small pots can still produce big plants if you water and feed often, which suits experienced growers rather than a first run. Pot size is a trade-off against watering and feeding frequency, not a fixed rule.

## How will you know it's working?

You'll know a soil grow is working when the pot cycles from heavy to light in 2–4 days and the plant stays a steady green:

- **Seedling:** sturdy stem, new true leaves every 3–5 days, no wilting despite the top drying.
- **Veg:** a new node every 2–4 days, leaves mid to deep green with no clawing ([clawing leaves](https://genetixbay.com/knowledge/diagnosis/clawing-leaves.md)) and no burnt tips ([brown tips](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md)).
- **Water:** plants perk up within an hour of watering and droop only when the pot is light.
- **Runoff:** pH 6.0–7.0 and EC within about 0.5 mS/cm of input.
- **Flower:** buds swell weekly; the oldest fan leaves yellow slowly in the last 2–3 weeks, which is normal senescence, not a reason to flush.

## What mistakes do beginners make in soil?

Soil beginners mostly drown their plants and overfeed them:

- **Overwatering**, especially seedlings in big pots. A heavy pot with droopy, firm leaves is drowning ([drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md)).
- **Feeding a "hot" mix** from day one. Let the starter charge run out first.
- **Full label strength.** Start at a quarter to half.
- **Garden soil in pots.** It compacts and carries pathogens [3].
- **Letting pots sit in runoff.** Empty saucers within 30 minutes.
- **Chasing pH.** A soil reading of 6.3 one day and 6.6 the next is normal drift.
- **Flushing at the end.** It costs yield and resin.
- **Ignoring fungus gnats.** Constantly wet tops breed them; let the top dry ([pest prevention](https://genetixbay.com/knowledge/guides/pest-prevention-for-beginners.md)).

## Evidence

- Container media need [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md); dense mixes waterlog: *Established* [1].
- Organic fertiliser rates in coir-based veg: *Supported* [2]. Higher nutrient strength not raising yield or cannabinoids: *Supported* [8].
- Avoiding garden soil and wet media to prevent damping-off: *Established* [3].
- Pot size and growth: *Established* across species [4]; the trade-off with feeding frequency is the house position.
- The 10–14 day transition: *Supported* [5]. Nitrogen trade-off: *Supported* [6]. Pre-harvest flushing: *Myth* [7].
- Week-by-week volumes and EC steps: *Grower practice*.

## Sources

1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5
2. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17
3. University of Minnesota Extension. How to prevent seedling damping off (sanitation; avoid garden soil in containers). https://extension.umn.edu/solve-problem/how-prevent-seedling-damping
4. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049
5. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153
6. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516
7. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25
8. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985