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; 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.
What do you need for a soil grow?
A soil grow needs the basic tent kit (choosing your setup) plus:
- [ ] Quality bagged potting mix, lightly amended (not a "hot" mix for seedlings), about 15–20 L (4–5 gal) per plant
- [ ] Perlite 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)
- [ ] EC meter (EC and ppm scales)
- [ ] 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 for fungus gnats
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 | 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 |
| 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 |
| 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 from week 15 |
| 17–20 | Harvest | Feed to the end; no flush | Harvest by trichomes, then dry |
Water volumes assume an LED 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).
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.
- 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].
- 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.
- Plant. Sow a cracked seed root-down 0.5–1 cm (¼–½ in) deep (germinating seeds), either straight into the final pot or into a 0.5–1 L cup.
- 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.
- 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). Autoflowers should start in the final pot.
- 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).
- 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].
- 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 benefit in a controlled study [8] (feeding basics).
- Train in veg. Bend and tie the main stem from week 4; tuck leaves to open bud sites rather than pluck them (training basics).
- 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.
- Check runoff every 1–2 weeks. Collect runoff and read pH and EC (runoff testing). Runoff EC much higher than input means salt build-up; much lower means the plant is hungry.
- 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).
- Harvest by trichomes (when to harvest), then dry and cure.
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. 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 to wash salt build-up 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) and no burnt tips (brown tips).
- 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).
- 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).
Evidence
- Container media need air-filled porosity; 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.
