How to grow tomatoes in pots: varieties, pot size, watering and feeding

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Tomatoes are one of the most rewarding things to grow on a balcony, patio or doorstep. They do not need a garden bed, but they do need more care in a pot than in the ground, because the roots have nowhere to go for water or food except the compost you give them. Get a few basics right and one plant can keep you in tomatoes for weeks.

Choose the right type

Tomato varieties fall into two broad groups, and the difference decides how much work you are signing up for.

Determinate (bush) types grow to a fixed size, set most of their fruit over a few weeks and then slow down. They are compact, need little or no pruning and suit smaller pots, troughs and even hanging baskets.
Indeterminate (cordon or vine) types keep growing and fruiting until the cold stops them. They get tall, need a stake or frame, and need their side shoots removed, but they crop for longer.

For a first try in a small space, a bush cherry tomato is the easiest win. If you have a sunny wall and want a long harvest, try a cordon.

Pot size and compost

Bigger is better, because a larger volume of compost dries out more slowly. The RHS suggests a pot of at least 30cm across for one plant, and up to 45cm for vigorous types; a standard growing bag holds two. Make sure there are drainage holes. Use fresh peat-free multi-purpose or loam-based compost rather than garden soil, which compacts in a pot. Mixing in some garden compost or a slow-release fertiliser at planting gives the plant a good start.

Planting and sun

Plant out only once the risk of frost has passed and nights are reliably mild.
Bury the stem deeper than it sat in its nursery pot; tomatoes grow roots along buried stem, which makes a sturdier plant.
Give them the sunniest, most sheltered spot you have. A south- or west-facing wall is ideal, and shelter matters because a tall plant in a pot is top-heavy.

Watering: the part that matters most

Most problems with potted tomatoes come back to watering. In hot weather a mature plant may need water at least once a day, sometimes twice. The goal is consistency. Compost that swings between bone dry and soaked causes two common problems:

Blossom end rot: a dark, sunken patch at the bottom of the fruit. It is caused by a shortage of calcium in the fruit, but the usual reason is irregular watering rather than a lack of calcium in the compost, because the plant can only move calcium in a steady flow of water. Plants in pots and growing bags are the most at risk. Affected fruits will not recover, so pick them off and keep watering evenly; later fruits are usually fine.
Split fruit: a heavy drink after a dry spell makes the skins burst.

Water the compost, not the leaves, and water thoroughly until it runs from the base. A saucer helps in a heatwave, but do not leave the pot standing in water for days.

Feeding

Once the first small fruits have formed, start feeding regularly with a liquid tomato feed, which is high in potash to support flowering and fruiting. Follow the label for dilution and frequency, which is often weekly or fortnightly. Do not pour feed onto dry compost; water first, then feed.

Support and side shoots

Put a cane or stake in at planting time so you do not spear the roots later, and tie the stem loosely as it grows.
On cordon types, pinch out the side shoots that appear in the angle between the main stem and a leaf stalk. Leaving them makes a bushy tangle with more leaves and smaller fruit. Pinch them while small with finger and thumb.
When a cordon reaches the top of its support or has set four or five trusses (flower clusters) outdoors, pinch out the growing tip so the plant puts its energy into ripening what it already has.
Bush types do not need side shoots removed.

Harvesting

Pick tomatoes when they are fully coloured and give slightly to a gentle squeeze. Picking regularly encourages more fruit. Towards the end of the season, green tomatoes will often ripen indoors in a warm spot, or they can be used green in chutney.

Common questions

Flowers dropping without fruit? Very hot or cold nights and dry compost are common causes. A gentle shake of the plant on a sunny day helps pollination.

Share a photo of your tomato pots, or ask about a problem with your plants, in the comments below.