Growing Tomatoes in Pots on a Sunny Patio

Choose a Big Pot and the Right Compost

Tomatoes are hungry, thirsty plants, and a pot is a very small patch of ground to grow them in. Give them room and they repay you generously; squeeze them and you will spend the summer fighting blossom end rot and wilting leaves. For a cordon variety, choose a container at least 35cm across and 30cm deep, holding 15 to 20 litres of compost. Bush and trailing types will manage in 10 to 12 litres, which makes them useful for hanging baskets and windowsills.

Terracotta looks lovely but dries out alarmingly fast in full sun. Glazed ceramic, plastic or fabric pots hold moisture far better, and pale colours keep the roots cooler on hot days. Whatever you choose, drainage holes are non-negotiable, and pot feet or bricks under the base stop water sitting beneath the pot.

Use fresh peat-free multipurpose compost, bulked out with a couple of handfuls of soil-based compost for weight and moisture retention, plus a slow-release fertiliser. Never reuse compost that has already grown tomatoes, as soil-borne problems build up quickly. If you are using a grow bag, ring culture works well: cut the bottom out of a large pot, sink it into the bag, and water and feed into the ring where the roots concentrate.

Plant deeply, burying the stem up to the lowest pair of leaves. Tomatoes root along that buried stem, which gives you a sturdier plant. Water in well, and in the UK wait until night temperatures are reliably above 10°C — usually late May or early June — before moving pots outside permanently.

Pick Varieties That Earn Their Space

Cherry tomatoes are the most forgiving choice for a patio, ripening earlier and cropping over a long season even in a mediocre summer. Among cordon (indeterminate) types, look for:

• Gardeners' Delight — a classic sweet cherry, generous and reliable.
• Sungold — exceptionally sweet orange cherries, though the thin skins split if watering is erratic.
• Shirley — a compact cordon with good-sized fruit, well suited to containers.
• Ferline or Crimson Crush — bred for better blight resistance, useful in a wet late summer.

For bush (determinate) varieties that need no pinching out, Tumbling Tom in red or yellow trails beautifully from a basket, while Totem stays neat and upright in a modest pot. Whichever you choose, cordons need staking and side-shoot removal; bush types do not.

Watering: Little, Often and Never Dry

Inconsistent watering is the single biggest cause of disappointing patio tomatoes. Let the compost dry out and then flood it, and the fruit will develop leathery brown patches of blossom end rot as calcium fails to reach the developing tomatoes. Aim for compost that is consistently moist, like a wrung-out sponge.

From July onwards, that usually means watering twice a day — early morning and again in the early evening — and perhaps a third time during a heatwave. Push a finger 2cm into the compost to check before you reach for the can. Water the compost, never the leaves, as wet foliage encourages blight. Empty saucers an hour after watering so roots are not left standing in cold water.

Self-watering pots and capillary matting take much of the guesswork out of a busy week. A mulch of gravel or grass clippings over the compost surface slows evaporation dramatically. In extreme heat, shade the pot itself rather than the leaves, so the roots stay cool.

Feeding for Fat Trusses

Begin feeding only when the first truss has set — that is, when you can see small green tomatoes the size of peas. Feed too early with a nitrogen-rich product and you will get a magnificent leafy plant and almost no fruit.

Use a high-potash tomato feed at the dilution on the bottle, once a week at first, increasing to twice weekly once the plants are carrying several trusses. If you see older leaves yellowing between the veins while the veins stay green, that is magnesium deficiency; a teaspoon of Epsom salts in a litre of water, watered into the pot or sprayed onto the leaves, usually corrects it within a fortnight.

Supporting and Pinching Out

Push a 1.8m cane into the pot before the plant gets big — afterwards you risk spearing the rootball. Tie the stem in every 20 to 30cm with soft twine, using a loose figure-of-eight so the stem is not strangled.

For cordon varieties, pinch out the side shoots that appear in the leaf joints while they are still small enough to nip between thumb and forefinger, leaving the flower trusses alone. Once four to six trusses have set, pinch out the growing tip in late July or early August. Our season is short, and stopping the plant concentrates its energy into ripening what is already there rather than producing more flowers that will never finish.

Ripening, Troubleshooting and a Late Bonus

From late August, ease back slightly on watering and feeding to encourage ripening, and remove the leaves below the lowest truss so light and air reach the fruit. This also reduces the chance of blight, that dreaded brown blotching of leaves and stems in a wet late summer. Remove affected foliage promptly, keep the foliage dry, and clear away fallen leaves.

• Whitefly and aphids: check leaf undersides and blast them off with a firm jet of water.
• Split fruit: usually a sign of erratic watering after a dry spell.
• Green fruit at the season's end: ripen it on a sunny windowsill beside a ripe banana, or turn it into green tomato chutney.

Finally, refresh the compost every year and move pots to a different spot where you can. A sheltered, south-facing corner, a big pot, steady watering and a weekly feed are all it takes to pick your own tomatoes from a patio well into autumn.