How to Grow Tomatoes on a UK Allotment (Even in a Rubbish Summer)

Tomatoes are the most popular allotment crop in the UK — and one of the most misunderstood. Grown well, a handful of plants will produce more fruit than a family can eat. Grown badly, they'll give you blight, blossom end rot, and bitter disappointment. This guide gives you everything you need to grow brilliant tomatoes on a UK allotment, even if the summer turns out to be a washout.

Choosing the Right Tomato Varieties for the UK

Variety choice matters enormously in the UK climate. Look for varieties described as 'outdoor', 'blight tolerant', or bred for cooler conditions. The best UK outdoor allotment varieties include:

• Gardener's Delight — classic cherry tomato, prolific, sweet, reliable outdoors

• Alicante — traditional salad tomato, performs well outdoors in most UK summers

• Tornado — bred for outdoor UK growing, compact, good blight resistance

• Sungold — exceptional flavour, orange cherry type, best under cover but does well outside in warm summers

• Mountain Magic — excellent blight resistance, medium-sized fruit, highly recommended for UK allotments

• Shirley — reliable salad type, good disease resistance, great for poly tunnels and outdoors

When to Sow Tomatoes in the UK

Sow indoors February–March, with bottom heat if possible (a heated propagator at 18–21°C gives much faster, more even germination). Tomatoes need 6–8 weeks of indoor growing before they're ready to plant out — if you sow too early without enough light, you'll get leggy, weak seedlings. A mid-March sowing is ideal for most UK growers without a heated greenhouse.

Growing On Indoors

Once seeds germinate, move to the brightest possible windowsill or a greenhouse. Pot on into individual 9cm pots when the first true leaves appear. Pot on again into 12–15cm pots as roots fill the smaller pot. By the time you plant out, you should have stocky, dark green plants about 20–30cm tall.

Hardening Off and Planting Out

Tomatoes are frost-tender. In the south of England, it's usually safe to plant out from late May; in the Midlands and north, wait until early June. Before planting out, harden off plants gradually over 7–10 days by putting them outside during the day and bringing them in at night. This acclimatises them to outdoor conditions and prevents transplant shock.

Spacing and Supports

Plant cordon (tall) varieties 45–60cm apart with a strong cane or stake at planting time. Bush varieties need 60cm spacing but no staking. Never crowd tomatoes — good airflow is the single best defence against blight and other diseases. Bury the stem slightly deeper than it was in the pot — tomatoes produce roots along the buried stem, giving a stronger, more drought-resistant plant.

Side Shooting Cordon Tomatoes

Cordon tomatoes produce side shoots that grow between the main stem and a leaf stem. Remove these when small by pinching between finger and thumb. Left to grow, they become full side stems and the plant becomes unmanageable. Check every 7–10 days throughout the season. Bush and tumbling varieties do not need side-shooting.

Watering Tomatoes

Inconsistent watering is the root cause of most tomato problems. Water deeply and regularly, keeping the soil evenly moist. Never let plants dry out completely then drench them — this causes split fruit, blossom end rot, and poor flavour. Always water at soil level, not on the foliage. Mulching around plants dramatically reduces watering frequency and keeps moisture more consistent.

Feeding Tomatoes

Start feeding once the first flowers open, using a high-potassium liquid feed (tomato feed) every week. Potassium drives fruiting; too much nitrogen gives you leafy plants with poor crops. Feed generously and consistently — tomatoes are heavy feeders. Homemade comfrey liquid feed is an excellent free alternative to bought tomato feed.

Preventing and Dealing with Blight

Late blight is the biggest threat to outdoor UK tomatoes, spreading rapidly in warm, wet conditions (typically July–August). Prevention: choose resistant varieties, space plants generously, remove lower leaves as plants grow, water at soil level only, and avoid watering in the evening. If blight strikes — brown patches on leaves and stems, fruit rotting — remove affected plants immediately. There is no cure.

Maximising Your Harvest

At the end of the season (late September), cut off the top of cordon plants to direct the plant's energy into ripening existing fruit rather than producing new growth. Bring green tomatoes indoors to ripen on a warm windowsill alongside a banana (the ethylene gas from the banana speeds ripening). Alternatively, make green tomato chutney — one of the great allotment traditions.