Short answer
In the ground, dig wide (about 60–90 cm, 2–3 ft) rather than just deep, blend in compost and coarse aeration, and aim for pH 6.0–7.0 and good drainage. In containers, use potting mix, and go big: about 75–380 L (20–100 US gal) for full-season photoperiods, 11–25 L (3–7 US gal) for autoflowers. Grower practice, consistent with container physics.
Why
Root volume sets the ceiling. Across many crops, bigger rooting volume generally means bigger plants [1]. House position: bigger pots give bigger yields within reason, but pot size is a trade-off against how often you can water and feed.
Air matters as much as water. A saturated medium has little air-filled porosity and roots suffocate; coarse material keeps pores open [2]. Clay that holds water after a day will do the same to roots in the ground.
Garden soil fails in pots. Confined in a container it compacts and can carry pathogens; potting mix is built for the job [3].
Outdoor sun dries pots fast. Small and fabric containers can dry within a day in summer, and dark pots heat the root zone above the 18–24 °C (64–75 °F) roots prefer.
The numbers
| Setup | Size | Notes |
|---|---|---|
| In-ground hole | ~60–90 cm (2–3 ft) wide, 45–60 cm (18–24 in) deep | Loosen the surrounding soil too |
| Raised bed or mound (clay) | 30–45 cm (12–18 in) high | Avoids a waterlogged "bucket" hole |
| Container, full-season photoperiod | ~75–380 L (20–100 US gal) | Bigger dries slower |
| Container, autoflower | 11–25 L (3–7 US gal) | Final pot from day one |
| Container mix | Potting mix + 20–35% perlite or pumice | No garden soil |
| Soil pH | 6.0–7.0 | Test before planting |
What to do
- Check local rules on outdoor growing first.
- Test drainage: water poured into the hole should be gone within a day.
- Test soil pH and correct it slowly if needed.
- On good soil, dig wide and blend in compost.
- On clay or rock, build a raised bed or use large containers.
- Mulch to keep roots cool; use light-coloured pots in hot climates.
Common mistakes
- A deep hole in clay backfilled with rich mix: a bathtub for roots.
- Garden soil in pots.
- Small pots in full summer sun.
Related
- Full article: Growing in soil (potting mix with bottled feed)
- Answers: Best soil for cannabis · Fabric vs plastic pots · Fix soil pH
- Terms: soil · outdoor growing
