# Growing in soil (potting mix with bottled feed)

> Soil (a peat- or compost-based potting mix fed with dilute bottled nutrients) is the most forgiving system: it buffers pH and nutrients and holds water for days. Water to light runoff when the pot is light, feed at EC 0.8–1.6 mS/cm with water at pH 6.2–6.8, and remember that over-watering, not under-feeding, kills most soil plants.

- Canonical: https://genetixbay.com/knowledge/systems/soil.html
- Category: Systems · Level: Beginner
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Any stage · 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

**Does a bigger pot give a bigger yield?** A bigger pot gives a bigger cannabis yield within reason: a meta-analysis of rooting volume across many crops found bigger root volume generally means bigger plants. Pot size is a trade-off with feeding frequency, though. GenetixBay's founder has grown over 4 ounces from a 16-ounce cup using [high-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md). Big pots are more forgiving but dry slower; small ones need frequent feeding.

**What pH should I water my soil plants at?** Water cannabis in soil at pH 6.2–6.8, within the accepted soil range of about 6.0–7.0. Compost and peat in the potting mix buffer pH, so a slightly off irrigation pH is absorbed for weeks. If you see mixed deficiencies despite feeding, check runoff pH and correct the water pH gradually rather than with harsh swings.

**How often should I water cannabis in soil?** Water cannabis in soil when the pot feels light and the top 2–3 cm (1 inch) is dry, rather than on a fixed schedule. Water slowly until 10–20% runs out, then discard the runoff. Learn the rhythm by lifting pots: water at roughly 40–50% of just-watered weight above [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md). Daily small sips that never fully wet the pot are a common mistake.

**Can I use hydro nutrients in soil?** Mineral nutrients can be used in soil only at soil strength, never at hydro strength on top of a fertilised mix. Wait until the mix's starter charge runs out, usually 2–4 weeks, then start at half the label rate, feeding at EC 0.8–1.6 mS/cm every second or third watering. Check runoff EC monthly, because a rising reading means salts are building up.

**What size pot do I need?** Photoperiod cannabis in soil usually finishes in an 11–25 litre (3–7 US gallon) pot, while autoflowers suit 11–15 litres (3–4 US gallons) planted directly into the final pot to avoid transplant stalls. Match the pot to how often you can water: smaller pots need more frequent feeding and watering, while bigger pots dry slower and forgive more.

**Why are my soil plants drooping when the soil is wet?** Soil plants droop when the soil is wet because they are over-watered: a saturated pot has little air-filled porosity, so roots suffocate and the plant wilts as if dry. Signs are droopy but firm-looking leaves, a heavy pot, slow growth and [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md). Water less often, add perlite or pumice to the mix, and consider fabric pots.

**Short answer.** "Soil" indoors means a bagged **potting mix** (peat or coco plus compost, perlite and a starter charge of fertiliser), not garden dirt. It is the most forgiving system: the mix buffers pH and holds nutrients and water for days. Water at **pH 6.2–6.8**, feed lightly (**EC 0.8–1.6 mS/cm**, i.e. 400–800 ppm500 / 560–1,120 ppm700) and only once the mix's own charge runs out, and water when the pot is **light**, to **10–20 % runoff**.

## How it works

The mix has three jobs: hold water, hold air, and hold nutrients on its exchange sites ([cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md)). Compost and peat buffer pH, so a slightly off irrigation pH is absorbed for weeks. Roots need air as much as water: a saturated pot has little air-filled porosity and roots suffocate. That is why [over-watering](https://genetixbay.com/knowledge/glossary/overwatering.md) looks like wilting [1].

## Numbers that matter

| Parameter | Target | Notes |
|---|---|---|
| Irrigation pH | 6.2–6.8 | Jardin "Soil (bottled feed)" band 6.3–6.8 [4] |
| Feed EC (when feeding) | 0.8–1.6 mS/cm | Jardin caps soil at ≤ 1.2 as default [4]; never hydro-strength |
| [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md) | Within ~0.5–1.0 of input | Rising runoff EC = [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) |
| Pot size, photoperiod | 11–25 L (3–7 US gal) final | Bigger pots dry slower and yield more within reason; smaller pots work if you water and feed more often (see note) |
| Pot size, autoflower | 11–15 L (3–4 US gal), plant directly | Avoid transplant stalls |
| Watering trigger | Pot ~40–50 % of its just-watered weight above dry weight | Learn by lifting |
| Root-zone temperature | 18–24 °C (64–75 °F) | |

> **House position: pot size is a trade-off.** Bigger pots give bigger yields, within reason; across many crops, bigger rooting volume generally means bigger plants (Poorter et al. 2012 meta-analysis). But root volume isn't the whole story: the founder has grown a QP+ (4 oz+, ~115 g+) from a 16 oz (~0.5 L) cup. If you push water and nutrients hard enough (high-frequency fertigation), big things come in small packages. Small pots need more frequent feeding and watering and leave less margin for error; big pots are more forgiving but dry slower. Match the pot to how often you can irrigate.

## How to run it

1. **Mix:** a quality potting mix with 20–35 % perlite or pumice. Garden soil compacts and carries pathogens [3].
2. **Start:** the mix's starter charge usually feeds seedlings for 2–4 weeks. Water only, pH-adjusted.
3. **Water:** when the pot is light and the top 2–3 cm (1 in) is dry. Slowly, until 10–20 % runs out. Discard runoff; don't let pots sit in it.
4. **Feed:** begin at half the label rate when lower leaves start to pale; feed every second or third watering ("feed, water, feed" is common).
5. **Check monthly:** pour-through or runoff EC/pH. If runoff EC climbs well above input, do a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md): 2–3× the pot volume of pH-adjusted water (pH ~6.3–6.8), slowly, then check runoff EC and go back to normal feeding.

## Failure modes

| Problem | Sign | Fix |
|---|---|---|
| Over-watering | Droopy, firm-looking leaves, wet heavy pot, slow growth, fungus gnats | Water less often, more air in mix, fabric pots |
| [Under-watering](https://genetixbay.com/knowledge/glossary/underwatering.md) | Limp, papery droop, very light pot | Water slowly in stages so the mix re-wets |
| Salt build-up | [Burnt tips](https://genetixbay.com/knowledge/glossary/nutrient-burn.md), runoff EC high | Root-zone flush (2–3× pot volume), then normal feed |
| [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md) | Mixed deficiencies despite feeding | Check runoff pH; adjust water pH, not with harsh swings |

## Jardin notes

Jardin medium "Soil (bottled feed)": moisture-based irrigation by VWC with long dry-downs, dosing caps halved, pH control on the water only, no reservoir pH-down below 6.0. Time-to-harm on pump failure: days. Automation level 2 [4].

## Common mistakes

- **[Flushing before harvest](https://genetixbay.com/knowledge/glossary/flushing.md).** Pre-harvest flushing is a *Myth* that costs you yield and resin: it starves the plant while it packs on its final weight, trichomes and resin. Feed through to harvest at stage strength. The only valid flush is a root-zone flush to clear salt build-up, at any stage (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)).
- Small cups watered daily "a little bit": the pot never dries and never fully wets.
- Hydro nutrient strength on top of a fertilised mix.
- Chasing every leaf spot by changing nutrients before checking runoff pH and watering rhythm.

## Evidence

Container-media physics is *Established* [1]. Feed ranges for mineral-fed soil are *Grower practice*; for organic liquid feed in coir-based organic substrates, ~389 mg N/L maximised veg yield in one study [2], which shows how much higher organic N rates can run than people expect, but it is not a mineral-soil recipe.

## 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. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins).
5. 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