How to Grow Tomatoes in Containers on a Balcony or Patio

Tomatoes are one of the most rewarding crops for a balcony or patio, and also one of the most demanding. A container tomato lives or dies by three decisions: which variety you plant, what goes into the pot with it, and how steadily it gets water. University extension services have clear guidance on all three.

Step 1: Pick the right growth type

South Dakota State University (SDSU) Extension splits tomatoes into two main growth habits, and the difference matters more in a pot than anywhere else:

• Determinate ("bush") tomatoes stop growing once they set fruit and produce their crop over a short period. They tend to be shorter, usually do not need staking, and SDSU says they work well in containers. Some are even sold as "patio" hybrids.
• Indeterminate tomatoes keep growing and producing until frost. They give a steady supply all season but need to be staked or caged.
• Semi-determinate varieties fall in between.

The seed packet or plant tag should say which type it is. The University of Wisconsin (UW) Extension's container guide adds that the trade-off with determinate types is a shorter harvest season, which may suit you or not. UW also notes that many cultivars are now bred specifically for containers, some very small, some fast to fruit, and some just compact versions of familiar varieties.

UW's sizing advice follows from growth habit: an indeterminate plant needs a container bigger than a 5-gallon bucket, while smaller determinate varieties can be grown in a 5-gallon bucket.

Step 2: Fill the pot with the right mix

UW's tomato container guide recommends a bagged soilless "potting mix," which is lighter than garden soil, so you can move the container, and is disease free. Its shopping list for one plant:

• A container at least as big as a 5-gallon bucket
• 25 quarts of potting mix
• 1/4 cup of slow-release fertilizer

UW also recommends adding garden lime to the mix, about 1 cup per 5-gallon container, adjusted for volume, so the plant has enough calcium. That calcium step connects directly to the most common container tomato problem, below.

After the first watering, UW says to leave about 1 inch of space at the top of the container so water does not run straight off the surface.

Step 3: Feed it through the season

UW points out that a soilless mix may not hold enough nutrients for a whole season. Check the bag's label; if more feeding is needed, use either a soluble fertilizer added when you water or a time-release product mixed in before planting. Smaller containers need more supplemental fertilizer than large ones.

SDSU adds a warning against overdoing nitrogen. Very dark, almost black-green leaves can signal too much nitrogen, which leads to lush leaves but little fruit, slower ripening, and more blossom end rot.

Step 4: Prevent blossom end rot

Blossom end rot is the dark, leathery patch that forms on the bottom of the fruit. SDSU and the University of Illinois Extension both stress that it is not a disease and not caused by insects. It is a calcium problem inside the fruit.

Illinois Extension explains the mechanism: plants take up calcium with water as leaves transpire, so anything that interrupts steady water uptake can starve the fruit of calcium. Its list of causes includes drought stress, inconsistent soil moisture, cold or waterlogged soil, and rapid leafy growth from too much nitrogen. High levels of ammonium, potassium, and magnesium, often from over-fertilizing, can also interfere.

Containers make this worse. Illinois Extension notes that containers dry out quickly, so potted tomatoes are more likely to develop blossom end rot without consistent watering, and that some soilless mixes are low in nutrients. SDSU adds that container plants in potting soil may need calcium added, since potting soils may not have enough.

Prevention steps from the three extension sources:

1. Add lime to the mix at planting (UW).
2. Water consistently. UW notes that in summer a container tomato can need water twice a day, especially in smaller pots, and that deeper containers help but still need a daily check. If you cannot water that often, UW suggests a container with a built-in water reservoir, or drilling drainage holes a few inches up the sides of a large container so the bottom holds a reserve.
3. Avoid heavy nitrogen and ammonium-based fertilizer during early fruiting (Illinois).
4. Mulch the surface to even out moisture (SDSU and Illinois).
5. Choose less susceptible types. Illinois names Celebrity, Mountain Pride, and cherry tomatoes; UW notes Roma types are much more susceptible than smaller, round-fruited ones.

Once a fruit has blossom end rot, Illinois says it cannot be fixed, and foliar calcium sprays do little because calcium does not move into the fruit well. Remove the damaged fruit and focus on the watering.

Heat, harvest, and storage

A few more numbers from SDSU that apply on a hot balcony:

• Tomatoes do best in temperatures above 50°F, so wait until after your last frost to set them outside.
• Above 95°F, fruit stops increasing in size, may not color properly, and blossoms may drop instead of setting fruit.
• It takes about 30 days from bloom until the fruit is full-sized and starts to ripen.
• Do not refrigerate ripe tomatoes; SDSU says cold ruins their flavor and texture.

Key takeaways

• Determinate ("bush" or "patio") tomatoes suit containers best; indeterminate types need a container larger than a 5-gallon bucket plus a stake or cage.
• UW Extension's one-plant recipe is about 25 quarts of soilless potting mix, 1/4 cup slow-release fertilizer, and about 1 cup of garden lime per 5 gallons.
• Blossom end rot is a calcium-delivery problem caused mostly by uneven watering, and containers are especially prone to it.
• Water deeply and consistently, mulch the surface, and avoid heavy nitrogen during early fruiting.
• Expect about 30 days from flower to full-sized fruit, and do not refrigerate ripe tomatoes.