Pot Size for Vegetables: Container Size Chart in Gallons

Pot Size Chart for Vegetables

Most leafy greens and root crops need a pot of 1/2 to 2 gallons, and most fruiting vegetables need 5 gallons per plant. The chart gives the minimum volume and depth for each crop, drawn from University of Maryland Extension and North Carolina State Extension container tables. Treat every number as a floor for a plant grown to full size.

Vegetable	Minimum pot volume	Minimum depth	Planting
Radishes	1 pint to 2 quarts	4 to 6 inches	2 to 3 inches apart
Leaf lettuce	1/2 gallon	6 to 8 inches	4 to 5 inches apart
Beets	1/2 gallon	8 inches	2 to 3 inches apart
Scallions	1/2 gallon	6 inches	2 to 3 inches apart
Spinach	1 gallon	4 to 6 inches	2 to 3 inches apart
Bush beans	2 gallons	8 to 10 inches	2 to 3 inches apart
Peas	2 gallons	12 inches	2 to 3 inches apart
Carrots	2 gallons	10 inches	2 to 3 inches apart
Swiss chard	2 gallons	8 inches	4 to 5 inches apart
Tomato, cherry	2 gallons	12 to 24 inches	1 plant
Kale	3 gallons	8 inches	6 inches apart
Collards	3 gallons	12 inches	12 inches apart
Cabbage	5 gallons		1 plant
Cucumber	5 gallons	8 inches	1 plant
Pepper	5 gallons	12 to 16 inches	1 plant
Eggplant	5 gallons	12 to 16 inches	1 plant
Tomato, standard	5 gallons	12 to 24 inches	1 plant
Summer squash	10 gallons	12 to 24 inches	1 plant

The two extension tables do not always agree, and the gaps are worth knowing. North Carolina State lists 2 gallons as the minimum for a pepper and for a squash plant and 1 gallon for a cucumber, where Maryland lists 5, 10 and 5. It also lists 2 quarts for carrots and for Swiss chard, where Maryland lists 2 gallons. The chart uses the larger figure in each case. A plant will live at the lower number, but it will need closer watching, because larger containers do not dry out as quickly and need water less often.

For crop ideas that suit these sizes, see vegetables for a balcony container garden.

Convert Pot Diameter to Gallons

Pots are sold by diameter and the chart is in gallons, so you need a conversion. University of Illinois Extension gives these soil volumes by diameter across the top of the pot:

Pot diameter	Soil volume
10 inches	3 gallons
12 inches	5 gallons
14 inches	7 gallons
16 inches	10 gallons
18 inches	15 gallons
24 inches	25 gallons

Read with the chart, that means a 12-inch pot is the entry size for one pepper or one eggplant, and a 16-inch pot covers a summer squash. Illinois sets its own minimum diameters a step higher for the big crops: more than 20 inches for tomatoes, more than 16 inches for peppers, more than 12 inches for carrots, and more than 10 inches for radishes, onions, beets, leafy greens and herbs.

For a container with no size on the label, measure it. For a round, straight-sided pot, multiply the radius in inches by itself, then by 3.14, then by the depth of mix, and divide by 231, the number of cubic inches in a US gallon. A pot 12 inches across and 12 inches deep works out to just under 6 gallons. Most pots taper toward the base, so the true figure runs lower, in line with the 5 gallons in the Illinois table.

Pot shape matters too. Container heights are usually sold as standard or azalea. Azalea pots are the shorter kind and suit plants with minimal roots, such as herbs.

Check Depth as Well as Gallons

Volume alone can mislead. North Carolina State says shallow-rooted vegetables such as lettuce, radishes and scallions need a minimum potting mix depth of 6 to 8 inches, and carrots grow better with 10 to 12 inches. Its table is a little more lenient for radishes and spinach, at 4 to 6 inches, and gives 10 inches as the floor for carrots. Peppers and eggplant are listed at 12 to 16 inches, and tomatoes at 12 to 24 inches.

A wide bowl planter is fine for a lettuce planting and wrong for a carrot or a pepper, even when the gallons add up. Count depth from the surface of the mix, and leave space between the mix and the rim so the pot can be watered properly.

Restricted roots mean a smaller plant. North Carolina State describes root restriction as a physical stress that causes a pronounced decrease in root and shoot growth. A plant that has stopped growing in midseason, or one with roots pushing out of the pot, has outgrown its container and should move to a larger one. The same signs apply indoors, covered in pot size for houseplants.

Pot Sizes for Herbs

Herbs need less room than vegetables. Most can be grown in a pot 4 to 6 inches in diameter. Herbs with a large taproot are the exception and need a container 12 inches deep.

Those small pots suit a windowsill, where you can check them daily. Outdoors in summer sun, a 10-inch pot, about 3 gallons, dries out less quickly and can carry several herbs together. Mint is best given a pot of its own because it spreads through the whole container, and the best pot for mint covers that case.

How Pot Size Changes Watering and Feeding

A small pot is a small water tank. Most outdoor containers need watering at least once a day when the plants are mature, and the 1/2 gallon and 1 gallon sizes on the chart reach that point first. Check every container daily in summer. Warm-season crops such as tomatoes and peppers also need 6 to 8 hours of direct sun, which speeds drying, while cool-season greens get by on 3 to 5 hours.

Container color and material add to the effect. Dark-colored containers absorb more heat than light ones and dry the mix faster, so avoid dark pots in full sun where you can, or go up a size. Terracotta, plastic and fabric pots compared explains how each material loses water, and watering containers in summer gives a routine.

Feeding follows the same logic, since frequent watering carries nutrients out of the mix. Long-season crops may need fertilizer every two weeks to keep producing. If you use a controlled-release product instead, plan to reapply in 8 to 10 weeks. Fertilizing container plants has the details.

Drainage and Weight: Two Limits on Size

Every container needs drainage holes, whatever its size. When a pot will sit on a solid surface such as a patio, the holes can go along the side, 1/4 inch to 1/2 inch from the bottom. Do not add a layer of gravel or rocks under the potting mix. It causes water to collect in the mix just above the gravel and takes depth away from the roots. Rocks in the bottom of a pot explains why.

Weight is the practical ceiling. A 20-inch container filled with potting mix and plants can weigh 100 pounds. Put large pots in their final position before filling them, or stand them on a rolling platform. On a balcony, check the load limit before lining up several 16-inch and 18-inch pots.

If a single tomato is your goal, growing tomatoes in 5-gallon buckets walks through the smallest setup that works, and grow bags for vegetables covers a lighter alternative to rigid pots.

Quick recap

• Greens and small roots: 1/2 to 2 gallons. Kale and collards: 3 gallons. Peppers, eggplant, cucumbers and standard tomatoes: 5 gallons each. Summer squash: 10 gallons.
• A 10-inch pot holds about 3 gallons, a 12-inch pot 5, a 14-inch pot 7 and a 16-inch pot 10.
• Depth is a separate test: 6 to 8 inches for lettuce and scallions, 10 to 12 for carrots, 12 or more for tomatoes, peppers and eggplant.
• Most herbs fit a 4 to 6 inch pot; taprooted herbs need 12 inches of depth.
• Small pots need water at least daily in summer, and a filled 20-inch container can weigh 100 pounds.