How to grow tomatoes in containers: determinate only, 5 gallons minimum

Why “determinate” is the only word that matters

Tomatoes come in two growth habits. Indeterminate plants keep growing until frost — in the ground that’s a 6–8 foot vine producing all summer. In a pot, it’s a 6-foot vine that outgrows its roots by July, wilts every afternoon, and sets a handful of fruit while you fight it with stakes. Determinate plants grow to a fixed size (usually 2–4 feet), set most of their fruit in a 3–4 week window, and are done. That sounds worse. In a container it’s exactly what you want: a plant whose appetite matches the pot.

Seed packets and nursery labels always say which. If it doesn’t say, assume indeterminate and put it back.

Varieties that actually work in pots

These are the ones I’ve grown on a 4×6 balcony across three seasons. Yields are per plant in a 7-gallon pot, so scale your expectations down for 5.

Container size: the 5-gallon floor

Five gallons is the smallest pot a bush tomato reliably fruits in. It’s not the best size — it’s the floor. Everything gets easier at 7 and noticeably better at 10: more even moisture, more root, more fruit. If you’re choosing between one 10-gallon and two 5-gallons, choose the one.

• Fabric grow bags (7–10 gal) — my default. Roots air-prune, they never waterlog, and they fold flat in winter. They do dry faster than plastic.
• Food-safe 5-gallon buckets — fine if you drill 6–8 drainage holes. Black buckets cook roots on a south-facing wall; paint them or wrap them.
• Self-watering planters — genuinely good for tomatoes because they hate uneven water. The reservoir needs refilling daily in July anyway.
• Terracotta — beautiful, heavy, and wicks water out of the mix. Use it for herbs, not tomatoes.

Depth matters as much as volume: plant the seedling deep, burying two-thirds of the stem. Tomatoes root along the buried stem, and in a pot that extra root is the difference between a plant that wilts at 2 pm and one that doesn’t.

Soil and feeding

Garden soil compacts into concrete in a container. Use a bagged potting mix — the potting soil guide covers which bags are actually mix and which are bark — and add a handful of slow-release tomato feed at planting. Once the first flowers open, switch to a liquid feed every two weeks. In August, stop. Late feeding grows leaves you don’t need and delays ripening.

Watering — the actual hard part

Every tomato problem people email me about comes back to water. Not too little: uneven. A pot that swings from bone-dry to soaked produces cracked fruit and blossom-end rot (that leathery black patch on the bottom of the tomato — it’s a calcium delivery problem caused by water gaps, not a calcium shortage, so skip the eggshells).

The routine that works: every morning in summer, lift or tip the pot. If it’s light, water slowly until it runs from the bottom. If it’s heavy, leave it. By July on a hot balcony this is daily, sometimes twice. A 2-inch mulch of straw or bark on the surface buys you hours.

Support and pruning

One bamboo cane and two soft ties. That’s it for a determinate. Don’t prune suckers — on a bush tomato every sucker is future fruit, and the “always pinch suckers” advice is written for indeterminates. Remove only leaves that touch the soil, to keep blight off.

Common failures and what they mean

Harvest

Pick when fully coloured but still firm, and twist rather than pull. A determinate will give you most of its crop in three to four weeks — plan to eat, freeze, or sauce. When the plant looks spent in late August, it is. Pull it, compost it, and sow lettuce in the pot for autumn.

Questions people actually ask