How to Grow Tomatoes in Containers on a Small Balcony

Sun and Reflected Heat

Clemson Extension says tomatoes need at least six hours of full sun, and UNH Extension recommends six to eight hours of direct sun. Watch how light moves across your balcony before you buy plants. Walls, glass and concrete can reflect and hold heat, which dries pots faster.

Wind and Safety

A leafy tomato plant can catch wind like a sail. Place heavy pots low and close to a wall or corner instead of on the railing, and tie supports to something solid. Wet potting mix is heavy, so check your building's rules and weight limits, spread large pots over the strongest parts of the floor, and keep exits clear.

Clemson Extension notes that indeterminate tomatoes keep growing taller until frost, which makes them hard to manage in containers. It recommends compact cultivars labeled "patio," "balcony" or "bush." UNH Extension recommends determinate patio or container varieties for pots, and the University of Minnesota says bush (determinate) types do not need pruning, staking or trellising.

Check the plant tag for these words:

• Determinate, bush or dwarf: plants that stop at a set height.
• Patio, balcony or container: varieties bred for pots.
• Cherry and grape types: small-fruited tomatoes are usually easy choices for containers.

Start with one or two well-cared-for plants. A single healthy plant usually does better than several crowded together.

Size recommendations vary by source and by variety. UNH Extension says four- to five-gallon containers are usually enough for individual plants of container varieties. Clemson says a 14- to 20-inch container suits most compact cultivars, and that a five-gallon bucket with drainage holes also works. Larger tomatoes need larger pots: a University of California fact sheet for container tomatoes recommends 15 to 20 gallons or more, at least 24 inches deep.

Whatever size you choose, the container needs drainage holes. Use a soilless potting mix made for containers, not garden soil. Dark containers can absorb heat in direct sun, so avoid placing them against a hot wall where you can.

The University of Minnesota says to plant tomatoes with part of the stem below the soil line, since new roots will form along the buried stem and give a stronger plant. The University of California recommends removing lower leaves so the plant sits deeper. Add support at planting time so you do not damage roots later.

1. Remove lower leaves: pinch off the bottom leaves of the seedling.
2. Plant deep: set the seedling so part of the bare stem is below the soil surface.
3. Firm and support: press the mix around the stem, and put a cage or stake in at planting. Clemson recommends supports for cultivars that grow taller than two feet.
4. Water thoroughly: water until it drains from the bottom holes.

Tomato flowers are self-pollinating. Clemson Extension says insects are not needed, and that wind provides enough movement under normal conditions. University of California advice notes that pollen moves by wind and pollinators, and that very enclosed spots with little air movement can need help, such as gently shaking the plants.

If flowers drop without setting fruit, temperature is a more common cause than pollination method. Clemson says daytime temperatures above 85°F can cause flowers to drop, as can several nights above 70°F, and that nights below 55°F can prevent pollination. If a heat wave is the cause, keep the plants watered and wait for cooler weather, moving pots away from hot walls if you can.

Watering

UNH Extension says container tomatoes need watering thoroughly at least once a day and possibly twice in hot weather. Clemson also notes daily watering may be needed at the height of summer. Water when the top two inches of the mix are dry, until water drains out. Water at the base instead of over the leaves, since wet foliage encourages disease.

Feeding

Frequent watering washes nutrients out of containers. Clemson suggests a balanced timed-release fertilizer at planting, or a water-soluble fertilizer weekly. UNH suggests weekly feeding starting two weeks after planting and favors products higher in phosphorus, and University of California advice favors a fertilizer lower in nitrogen. Too much nitrogen can encourage leaves over fruit. Follow the product label.

Support and Pruning

Tie cages or stakes to a solid support with soft ties. Bush types need little pruning, so remove only damaged or yellowing leaves near the base to keep air moving.

The University of Minnesota says blossom-end rot can develop when soil moisture fluctuates during fruit growth, and the University of Maryland notes it is linked to inconsistent or shallow watering and excess nitrogen. The University of Minnesota says growth cracks happen when fruit grows too fast, most often during heavy rain and warm temperatures.

Tomatoes are usually best left to ripen on the plant, but on a windy or very hot balcony you can pick fruit once it has started to color and finish ripening indoors. The University of Minnesota says mature fruit that is fully sized but not yet colored will often ripen satisfactorily, and that warm temperatures matter more than light for ripening. Keep picked fruit at room temperature instead of in the refrigerator.

• Clemson Cooperative Extension, "Tomatoes in Containers"
• Clemson Cooperative Extension, "Why Did My Tomatoes Stop Producing Fruit?"
• University of New Hampshire Extension, "What is the best way to grow tomatoes in a container?"
• University of Minnesota Extension, "Growing tomatoes in home gardens"
• University of Maryland Extension, "Key to Common Problems of Tomatoes"
• UC ANR, "Growing Container Tomatoes in San Francisco"
• UC ANR, "Shake the tomato plants?"