Choosing the Best Containers for a Balcony Vegetable Garden

Size by Soil Volume First

The best container for a balcony vegetable garden is a plastic, resin or fabric pot that holds enough potting mix for the crop and drains freely. Volume matters more than material. University of Maryland Extension sets the minimums at 1 to 3 gallons of growing media for herbs and salad greens, 4 to 6 gallons for beans and summer squash, and 8 to 10 gallons for a full-size tomato, pepper or eggplant.

Those numbers are floors. A pot below the minimum dries out between waterings and leaves roots with nowhere to go, and no feeding schedule makes up for it. The same publication gives a depth for each group, which is worth checking on wide, shallow bowls that look bigger than they are.

Crop group	Examples	Minimum growing media	Depth
Small	Basil, cilantro, radish, scallions, spinach, salad greens	1 to 3 gallons	4 to 6 inches
Medium	Beans, summer squash, cole crops, dwarf tomato, dwarf pepper, dwarf eggplant	4 to 6 gallons	8 to 12 inches
Large	Tomato, pepper, eggplant, cucumber, winter squash	8 to 10 gallons	12 to 16 inches
Potatoes	One planting	30 gallons	Not listed

Potatoes stand apart at 30 gallons of potting mix, which is a lot of weight for a balcony. If you want tomatoes in less space, a dwarf or compact variety in the medium group is the honest route. The difference between plant types is covered in the guide to determinate and indeterminate tomatoes.

University of Maryland Extension also publishes a crop-by-crop table with different floors: 5 gallons for one standard tomato, pepper, eggplant or cucumber, 2 gallons for a cherry tomato and 10 gallons for a summer squash. Where the two tables differ, the larger figure gives you more margin on a hot balcony. The pot size chart for vegetables lists every crop.

Check Weight, Sun and Wind Before You Buy

Three balcony conditions narrow the choice before material comes into it.

Weight comes first. University of Maryland Extension notes that a 20-inch diameter container filled with moist potting mix and plants can weigh 100 pounds. Several of those add up quickly, so if you rent or live in an older building, ask the building manager what the balcony is rated to carry before you fill large pots.

Sun decides the crop list, and the crop list decides the pot sizes. Warm-season crops such as tomato, pepper, eggplant and squash need 6 to 8 hours of direct sun. Cool-season crops such as lettuce, spinach and Asian greens manage on 3 to 5 hours. A balcony with only morning sun is a greens-and-herbs balcony, and that means small, shallow containers will do.

Wind works against you in two ways. Breezes dry container media faster than a sheltered spot does, and tall plants in small, lightweight containers can blow over or become top-heavy unless they are well anchored. On an exposed balcony, choose a wider pot than the minimum, install stakes and supports while plants are young, and tuck the tallest crops into the most sheltered corner.

Compare Container Materials

The useful distinction between materials is whether the walls are porous. NC State Extension sorts them into three groups: nonporous (plastic, metal, fiberglass, glazed pots), semi-porous (wood, pressed fiber) and porous (clay, unglazed ceramic, terracotta). Porous and semi-porous containers lose moisture more quickly and need more frequent watering.

Material	Porosity	Watch for
Plastic or resin	Nonporous	Plastics not made for outdoor use turn brittle
Fabric grow bag	Breathable fabric	Soil can dry out quickly
Glazed ceramic	Nonporous	Dark glazes heat up in full sun
Unglazed clay or terracotta	Porous	Dries fast; cracks if left out in freezing weather
Wood	Semi-porous	Dries faster than plastic
Metal	Nonporous	Heat in full sun when dark colored
Self-watering	Reservoir under the mix	Reservoir still needs filling in summer

Plastic and resin suit most balconies because nonporous walls hold moisture, which matters where wind and sun dry pots quickly. Look for pots sold for outdoor use, since plastics not made for it can turn brittle.

Fabric grow bags are lightweight and easy to move. Rutgers Cooperative Extension describes how roots that reach the fabric wall meet drier soil and more air and stop growing, which prompts the plant to make new roots instead of circling. The bags drain well, are hard to overwater and store easily when empty. The cost is water: they need more of it than some traditional containers. Rutgers advises starting with at least a 5-gallon bag for one plant.

Unglazed clay is porous, so it loses moisture more quickly than plastic and needs watering more often, and a breezy balcony adds to that. The differences are compared in more detail in terracotta, plastic and fabric pots. NC State also warns against leaving unglazed ceramic outside over winter, because the walls absorb water that freezes and cracks the pot.

Color matters as well as material. Dark-colored containers absorb more heat than light-colored ones, the mix dries faster, and University of Maryland Extension notes that the higher temperatures can injure young roots. NC State’s advice is to avoid placing dark containers in full sun.

Which Container for Which Balcony

Match the container to the condition that limits you most.

A renter who expects to move does well with fabric grow bags of 5 gallons or more. They are lightweight and easy to store when not in use. A grower on a hot, sunny balcony who misses waterings should look at self-watering containers. A windy, exposed balcony calls for wide plastic or resin pots with stakes set early. If the space gets only 3 to 5 hours of direct sun, long plastic boxes in the 1 to 3 gallon range will carry lettuce, spinach and herbs, and succession planting lettuce keeps those boxes full. Wherever pots stay out through freezing winters, pass on unglazed clay.

How Self-Watering Containers Work

In a self-watering container the growing medium sits on a perforated platform directly above a water reservoir, and water wicks up into the mix. Because the reservoir catches what would otherwise drain away, water and nutrients are not wasted, and nothing drips onto the balcony below.

They reduce the work but do not remove it. University of Maryland Extension describes a homemade version that holds about 4 gallons of moistened medium. In full sun in July and August it needs topping up every day, and it takes 1 to 2 quarts each day to fill the reservoir. In milder weather the same publication says these containers make it possible to ignore your pots for a few days.

Drainage Holes, Saucers and What Not to Add

Every container except the self-watering type needs holes or slits in the bottom so excess water can leave. Most garden pots are sold with them, but not all, so check before you buy. NC State notes that holes can also be placed along the side of the container, 1/4 inch to 1/2 inch from the bottom.

Do not add a layer of gravel, rocks or broken pot shards under the mix. Both University of Maryland Extension and NC State advise against it. It does not improve drainage and may raise the water table inside the pot, which puts the wet zone closer to the roots. Fill the whole container with potting mix. What to look for in the bag is covered in the guide to potting mix for containers.

On a balcony the water has to go somewhere. University of Maryland Extension points out that saucers help when you garden above a neighbor’s balcony. Empty them regularly so the collected water does not encourage root rot or give mosquitoes a place to breed.