Guide
Container size chart: pot depth and volume by vegetable
Most container failures trace back to a pot that was too small for the crop. Here are the standard minimums extension publications converge on, crop by crop.
How to read the chart
Two numbers matter and they answer different questions. Depth is set by the root system: it's a hard minimum, and no amount of width makes up for missing it. Volume is what the pot can hold in water and nutrients between waterings; a plant squeezed into the minimum will grow, but it dries out faster and needs feeding more often. Where the chart gives a range, the low end is "it will work with attention" and the high end is "it will work while you're away for a weekend."
Plants per pot assumes the recommended volume, not the minimum. For crops planted many-per-pot, like lettuce and radishes, the counts follow the same spacing logic as our square-foot planting chart — a 12-inch-wide pot is roughly one square foot of surface.
The chart
| Crop | Min. depth | Recommended volume | Plants per pot |
|---|---|---|---|
| Tomato, indeterminate | 12 in / 30 cm | 15–20 gal / 57–76 L | 1 |
| Tomato, determinate or patio | 10–12 in / 25–30 cm | 5–10 gal / 19–38 L | 1 |
| Pepper | 10–12 in / 25–30 cm | 3–5 gal / 11–19 L | 1 |
| Eggplant | 12 in / 30 cm | 5 gal / 19 L | 1 |
| Cucumber, bush type | 12 in / 30 cm | 5 gal / 19 L | 1–2 |
| Zucchini / summer squash | 12–14 in / 30–36 cm | 5–10 gal / 19–38 L | 1 |
| Potato | 16 in / 41 cm | 10–15 gal / 38–57 L | 1–2 seed pieces |
| Bush beans | 8–9 in / 20–23 cm | 2–3 gal / 8–11 L | 4–6 per 12-in pot |
| Peas | 8–10 in / 20–25 cm | 2–3 gal / 8–11 L | 6–9 per 12-in pot |
| Carrot, short varieties | 8–12 in / 20–30 cm | 2–5 gal / 8–19 L | 16 per 12-in pot |
| Beet | 8–10 in / 20–25 cm | 2–3 gal / 8–11 L | 9 per 12-in pot |
| Radish | 6 in / 15 cm | 1–2 gal / 4–8 L | 16 per 12-in pot |
| Onion, green | 6 in / 15 cm | 1–2 gal / 4–8 L | 16 per 12-in pot |
| Lettuce, leaf | 6 in / 15 cm | 1–2 gal / 4–8 L | 4–6 per 12-in pot |
| Spinach | 6–8 in / 15–20 cm | 1–2 gal / 4–8 L | 9 per 12-in pot |
| Kale | 8–10 in / 20–25 cm | 3–5 gal / 11–19 L | 1–2 |
| Swiss chard | 8–10 in / 20–25 cm | 2–3 gal / 8–11 L | 2–3 |
| Basil | 8 in / 20 cm | 1–2 gal / 4–8 L | 1–3 |
| Parsley / cilantro | 8 in / 20 cm | 1–2 gal / 4–8 L | 2–3 |
| Thyme / oregano | 6–8 in / 15–20 cm | 1–2 gal / 4–8 L | 1–2 |
| Strawberry | 6–8 in / 15–20 cm | 1–2 gal / 4–8 L | 3–4 per 12-in pot |
These are consensus ranges from US extension-service container guides. Individual varieties move the numbers: a "Tumbling Tom" tomato is bred for a hanging basket, while a full-size 'Brandywine' will sulk in anything under 15 gallons; 'Paris Market' round carrots manage in 6 inches while standard 'Danvers' types want 12.
What happens when the pot is too small
An undersized container doesn't kill a plant outright — it caps it. Roots circle the pot wall, the mix dries out within hours on a hot day, and the plant responds by staying small and dropping flowers. Fruiting crops show it worst: a pepper in a 1-gallon pot will produce a handful of small fruit where the same plant in 3 gallons would produce steadily all season. If a plant needs water twice a day just to stay upright, the pot is too small, not the schedule — the same signal we cover from the other direction in the watering schedule guide.
Material matters less than size, with one exception
Plastic, fabric grow bags, glazed ceramic, and wood all grow the same vegetables at the same sizes; pick by weight, price, and looks. The exception is unglazed terracotta, which breathes water out through its walls — a terracotta pot at the minimum volume dries out meaningfully faster than a plastic one, so treat terracotta minimums as one size larger. Fabric bags air-prune roots and forgive overwatering, which makes them the safest choice at the small end of a crop's range, and their labeled sizes are honest liquid gallons rather than trade gallons.
Bigger pots are heavier pots
On a balcony, the ceiling isn't just space — a 15-gallon container of watered mix is a serious amount of weight, and several of them concentrated in one spot can approach what a balcony floor is designed for. Before scaling up to tomato-sized containers, run the numbers in our container soil weight chart against your building's limits.