How Deep Do Pots Need to Be? A Simple Container Depth Guide
How deep containers need to be for herbs, salad, root vegetables and larger crops — a quick reference for choosing pots.
Pot depth decides how much root room, water and nutrients a plant has. Too shallow and it dries out hourly in summer; deeper is almost always better on a balcony.
Why depth matters more in containers
- Effective rooting depth
The depth of soil a plant’s roots actually use. In the ground, roots can search wider and deeper for water. In a pot, they’re capped — so the container has to hold enough moisture and feed to last between waterings.
A shallow, wide pot also heats up and dries faster because more of its volume is near the surface. A deeper pot of the same width stays cooler and needs watering less often.
Minimum depth by crop
| Crop | Minimum depth | Notes |
|---|---|---|
| Salad leaves, rocket | 15 cm | Wide trough works well; harvest young |
| Radish | 15 cm | Loose mix, thin seedlings early |
| Basil, parsley, coriander | 20 cm | Keep evenly moist |
| Mint | 20 cm | Grow in its own pot — it spreads |
| Chard, spinach | 25 cm | Tolerates part shade |
| Bush beans | 25 cm | Support with short twigs |
| Tomatoes, peppers, chillies | 30 cm | One plant per pot; feed weekly |
| Courgette | 40 cm | Needs a wide pot too, 40 cm+ across |
| Potatoes | 40 cm+ | Earth up as shoots grow |
| Carrots | 30 cm+ | Stone-free mix for straight roots |
Planning a whole balcony from scratch? See the beginner’s guide to starting a balcony garden.
Frequently asked questions
Can I grow tomatoes in a 20 cm pot?
You can get a small harvest from a dwarf or trailing variety, but the plant will need watering once or twice a day in summer and will crop far better in a 30 cm or larger pot.
Are grow bags deep enough for vegetables?
Standard grow bags are about 18 cm deep, which suits salad, herbs and bush beans. Stand them on their end, or use a tall planter, for tomatoes and peppers.
Does a deeper pot need more drainage?
It needs the same open drainage holes, but a deep pot holds a wetter zone at the bottom. A few centimetres of gravel and a free-draining peat-free mix keep roots healthy.