# How should I prepare soil or pots for outdoor plants?

> For outdoor cannabis in the ground, dig a hole about 60–90 cm (2–3 ft) wide and 45–60 cm (18–24 in) deep, mix in compost and perlite or pumice, and aim for soil pH 6.0–7.0 with good drainage. In containers, use potting mix, not garden soil: about 75–380 L (20–100 US gal) for full-season photoperiods and 11–25 L (3–7 US gal) for autoflowers. Bigger holds more water.

- Canonical: https://genetixbay.com/knowledge/answers/outdoor-soil-and-pot-size.html
- Topic: Outdoor growing · Type: How-to
- Evidence: Grower practice · Status: Draft: awaiting expert review
- Full article: [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md)
- Also asked as: How big a hole for an outdoor cannabis plant? | Should I grow in the ground or in pots outdoors? | What size container for outdoor cannabis? | How do I amend clay soil for cannabis? | Can I use garden soil in pots?
- 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)"

## 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](https://genetixbay.com/knowledge/glossary/ph.md) 6.0–7.0 and good [drainage](https://genetixbay.com/knowledge/glossary/runoff.md). In containers, use [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), and go big: about 75–380 L (20–100 US gal) for full-season [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md), 11–25 L (3–7 US gal) for [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md). *Grower practice*, consistent with container physics.

## Why

[Root volume](https://genetixbay.com/knowledge/glossary/pot-size.md) sets the ceiling. Across many crops, bigger rooting volume generally means bigger plants [1]. House position: bigger pots give bigger [yields](https://genetixbay.com/knowledge/glossary/yield.md) 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](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) 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](https://genetixbay.com/knowledge/glossary/root-zone.md) 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](https://genetixbay.com/knowledge/glossary/overwatering.md) "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](https://genetixbay.com/knowledge/glossary/perlite.md) or pumice | No garden soil |
| Soil pH | 6.0–7.0 | Test before planting |

## What to do

1. Check local rules on outdoor growing first.
2. Test drainage: water poured into the hole should be gone within a day.
3. Test soil pH and correct it slowly if needed.
4. On good soil, dig wide and blend in compost.
5. On clay or rock, build a raised bed or use large containers.
6. 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)](https://genetixbay.com/knowledge/systems/soil.md)
- Answers: [Best soil for cannabis](https://genetixbay.com/knowledge/answers/best-soil-for-cannabis.md) · [Fabric vs plastic pots](https://genetixbay.com/knowledge/answers/fabric-pots-vs-plastic-pots.md) · [Fix soil pH](https://genetixbay.com/knowledge/answers/fix-soil-ph.md)
- Terms: [soil](https://genetixbay.com/knowledge/glossary/soil.md) · [outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md)

## Follow-up questions

**Is it better to grow cannabis in the ground or in pots outdoors?** Growing cannabis in the ground gives the biggest outdoor plants, because roots are unlimited and the soil buffers water for days. Pots let you move plants, control the mix and grow where the native soil is poor, but they dry fast in summer sun and cap plant size. Choose the ground if your soil drains well; pots or raised beds if it doesn't.

**How do I grow cannabis in clay soil?** To grow cannabis in heavy clay, don't dig a deep hole and backfill it with rich mix, because the hole can fill with water like a bucket. Build a raised bed or mound 30–45 cm (12–18 in) high instead, or dig wide and shallow and blend compost plus coarse material into a large area. Test drainage first: water should not still be standing after a day.

**Can I use garden soil in containers?** Don't use garden soil in containers for cannabis. Dug soil compacts in a pot, drains poorly, starves roots of air and can carry soil-borne pathogens. Use a bagged potting mix with about 20–35% perlite or pumice instead. Garden soil is fine for in-ground planting where it drains well, improved with compost, but it behaves very differently once confined in a pot.

## Sources

1. 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
2. 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
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