Start with varieties that suit a pot, not a plot

A patio is a demanding spot for a tomato. Space is tight, the roots have nowhere to run, and the compost dries out far faster than soil in a border. The single biggest decision you will make is variety, so choose one bred to stay small. Bush, dwarf and trailing types do far better in containers than the tall cordon varieties that would need staking to head height.

Reliable choices for a sunny patio include:

• Trailing types such as 'Tumbling Tom' — happy in a pot at knee height or a hanging basket, with fruit that hangs clear of the foliage.
• Compact cherries such as 'Garden Pearl' — generous croppers with sweet, thin-skinned fruit that ripens quickly in a British summer.
• A blight-resistant variety such as 'Crimson Crush' — worth the few extra pence per seed if your patio is open to the weather.

Cherry tomatoes are generally the safest bet in pots, because fast ripening matters when August turns cool and damp. Save the big beefsteak types for a greenhouse.

Choose the right pot, compost and position

Size matters more than most people expect. A single tomato plant wants at least 10 litres of compost and 15 litres is better, which means a pot roughly 30cm across. Anything smaller and you will spend the whole summer chasing the watering can. Terracotta looks lovely but dries out quickly in full sun, so glazed ceramic, plastic or a fabric planter will hold moisture for longer. Whatever you choose, it must have drainage holes and it should stand on pot feet so surplus water can escape freely.

Fill with a good-quality peat-free multipurpose compost, mixed with a handful of slow-release tomato fertiliser and a little water-retaining gel if you find pots dry out fast. Don't reuse last year's compost — it will have lost its structure and may carry disease.

Siting is straightforward: full sun, six hours a day at minimum, ideally against a south- or west-facing wall. That wall radiates warmth back overnight and shelters the plants from wind, but do leave some air moving around them. A crowded, stuffy corner is an invitation to mould and blight.

Plant up and give them support

Plant deep. Bury the stem up to the first set of leaves, because tomatoes will root along the buried stem and you will end up with a sturdier plant. Firm the compost gently, water in well, and keep the surface clear of fallen leaves.

Even bush varieties benefit from a little support once the fruit sets. Push three short canes around the edge of the pot and loop twine around them, or use a single cane with soft ties that you check weekly so they never cut into the stem. If you are growing a cordon variety, pinch out the side shoots that appear in the leaf joints and stop the plant once four or five trusses have set. Anything beyond that will not ripen in time.

Water little and often

This is the phrase that matters most. Tomatoes hate extremes. A plant that dries out and is then flooded will split its fruit and develop blossom end rot — a black, sunken patch at the base of the tomato caused by poor calcium uptake when moisture levels swing about.

In a normal British summer, one thorough watering a day is usually enough in a 15-litre pot. In a heatwave, that becomes two: one in the morning and one in the early evening. Always water the compost rather than the leaves, and keep going until water runs out of the drainage holes. Shallow sprinkling only wets the surface and encourages weak roots.

• Stand pots on saucers in July and August to catch run-off, but empty them if rain is forecast.
• A 2cm mulch of compost or gravel over the surface slows evaporation considerably.
• Rainwater from a butt is better than tap water — it is softer and warmer, which the roots prefer.

Feed once the flowers appear

Don't feed too early. Until the first flowers open, the compost holds plenty of nutrients, and extra nitrogen will simply give you a handsome plant with very little fruit. Wait until the first truss has set — you will see tiny green tomatoes sitting behind the faded flowers — then start feeding with a high-potash tomato fertiliser.

Dilute it according to the bottle, give one dose a week at first, and increase to twice a week once the plant is carrying several trusses. Always feed when the compost is already damp, never onto dry roots, and never exceed the recommended strength in the hope of a bigger crop.

If leaves yellow between the veins while the edges stay green, the plant is short of magnesium. A diluted Epsom salt spray over the foliage, given once a fortnight, usually sorts it out.

Ripen, pick and keep problems at bay

As fruit begins to colour, remove the leaves below the lowest trusses so light and air reach the tomatoes. Pick regularly — a plant carrying ripe fruit slows down production, so harvesting little and often keeps the crop coming right into September.

Blight is the main outdoor risk in a wet summer: brown patches on leaves and stems that spread alarmingly fast. Remove affected foliage straight away, keep the leaves as dry as you can, and choose resistant varieties next year. If blight takes hold, harvest the green tomatoes and ripen them indoors on a windowsill or in a paper-lined drawer with a ripe banana, which speeds things along.

Move pots under cover towards the end of September if you can, and give any remaining green fruit a fortnight on a sunny sill. Nothing quite matches the flavour of a tomato picked warm from the plant on your own patio, and a couple of well-chosen pots will keep you in fruit from July until the first frosts.