Choosing the right varieties for our weather

Tomatoes are sun-loving plants, and a British summer rarely offers the long, hot, reliably dry days they would choose for themselves. That does not mean outdoor tomatoes are a lost cause — far from it. It simply means picking varieties with our climate in mind, rather than copying what works in a Mediterranean garden.

Blight is the single biggest threat to outdoor tomatoes in the UK, especially in wet, humid summers and in the damp west. Look for varieties bred for resistance: 'Crimson Crush', 'Ferline' and 'Mountain Magic' all shrug off blight far better than older types. Reliable favourites such as 'Gardener's Delight', 'Ailsa Craig' and 'Moneymaker' still perform well in a decent year, while ultra-early types like 'Sub Arctic Plenty' and compact bush tomatoes such as 'Red Alert' and 'Tumbling Tom' crop quickly in short seasons.

Think about habit, too. Cordon (indeterminate) varieties grow tall and need staking and side-shooting; bush (determinate) varieties stay compact and suit pots, grow bags and exposed plots. In a short season, a bush tomato in a large pot on a sunny patio often beats a cordon struggling in open ground.

Starting seeds under cover

Outdoor tomatoes need a long head start. Sow indoors or under cover in late March to early April — sow too early in February and you will raise leggy, pale plants that sulk for weeks before planting out. A warm windowsill, a heated propagator or a greenhouse bench all work well.

• Sow seeds about 1.5cm deep in moist seed compost, one or two per small module or pot.
• Germinate at 18–21°C. Seedlings usually appear within 7–14 days.
• Move seedlings into bright light immediately; a south-facing windowsill is ideal, but turn pots daily so stems stay straight.
• Prick out into 9cm pots once the first true leaves appear, then pot on again into 12–15cm pots when roots fill the compost.
• Keep compost just moist. Damping off thrives in cold, sodden soil.

Aim for stocky, dark green plants around 15–20cm tall by planting-out time, not wispy giants. If growth is pale or spindly, more light is almost always the answer.

Hardening off and moving plants outdoors

Tomatoes raised indoors have soft, tender growth and will scorch or stall if thrown straight outside. Harden them off over 7–10 days, ideally starting in mid-May in the south and late May further north.

• Day one: an hour outdoors in shade on a mild day.
• Days two to four: extend the time, gradually introducing morning sun.
• Days five to seven: leave them out for most of the day, in sun and gentle wind.
• Nights: bring them in at first, then leave them out once temperatures stay above roughly 10°C.

Plant out only after the last frost risk has passed — usually late May in southern England, early June in the north and in Scotland. If a cold snap is forecast, fleece or cloches will buy you a few precious degrees.

Siting, planting and early care

Choose the sunniest, most sheltered spot you have: a south-facing wall, a patio corner or beside a fence. Tomatoes hate cold wind and waterlogged roots. Improve the ground with plenty of garden compost and a handful of general-purpose fertiliser, or grow in large pots and grow bags filled with fresh, peat-free compost.

Plant cordons 45–60cm apart and bush varieties a little closer, burying the stem up to the first set of leaves — tomatoes root readily along the buried stem and this makes for sturdier plants. Water them in well, then stake cordons immediately with a sturdy cane. A plastic collar around the stem deters cutworms and keeps young plants protected.

Feeding, watering and training

Consistency matters more than quantity. Water thoroughly two or three times a week rather than little and often, aiming at the soil, never the leaves, and preferably in the morning. Erratic watering causes split fruit and blossom end rot.

Start feeding with a high-potash tomato fertiliser once the first truss of flowers has set fruit, usually from late June. Follow the label — overfeeding encourages leafy growth at the expense of fruit.

For cordons, pinch out the side shoots in the leaf joints each week, and tie the main stem to its cane as it grows. Remove lower leaves once fruit has set to improve airflow. In late August or early September, pinch out the growing tip to push energy into ripening the fruit already set. Bush varieties need no side-shooting — just a little support to keep heavy trusses off the ground.

Troubles, ripening and the final harvest

Blight shows as brown-black patches on leaves and stems, often after warm, wet spells. Act fast: remove affected foliage, improve ventilation and avoid overhead watering. Plants under a porch overhang or a simple polythene shelter stand a much better chance. Aphids, whitefly and red spider mite are the other common visitors; a strong jet of water and encouragement of ladybirds usually keep them in check.

Fruit ripens from July through to October, depending on variety and weather. As the season cools, pick any remaining green tomatoes before the first hard frost and ripen them indoors on a sunny windowsill or in a drawer with a ripe banana. They will colour up slowly and taste far better than anything flown in.