How to Grow Tomatoes: From Seed to Harvest in the UK

Grow tomatoes in the UK from seed to harvest. Learn when to sow indoors, when to plant out, how to water and feed, and how to prevent common problems.

Quick answer

Tomatoes can crop well in UK gardens, especially under cover or in sunny, sheltered positions. Sow greenhouse tomatoes indoors from late February to mid-March, or sow from late March to early April for outdoor plants. Pot on as seedlings grow, and move outdoor plants into their final position after frost risk has passed. Many varieties ripen from July to early autumn, depending on the weather.

Overview

Tomatoes (Solanum lycopersicum) are one of the UK's most popular crops to grow at home. They reward a warm start, plenty of light and consistent watering. Actual yields vary considerably with the variety, container size, temperature and growing conditions.

In the UK, tomatoes do best under cover — a greenhouse, a polytunnel, or a bright south-facing windowsill. Outdoor bush types are worth a punt in a warm summer, but you need to choose varieties bred for cooler, shorter seasons and accept that a wet August can take the lot. This guide covers both indoor and outdoor growing, and walks you from sowing seed through to your last harvest of the year.

When to Start in the UK

Tomatoes want a long, warm growing season — and the UK doesn't give them one for free. You start them early indoors, then move plants out only when conditions are safe.

• Sow seed: late February to mid-March for greenhouse crops, or late March to early April for outdoor crops. Use a heated propagator set to 18–21°C. For greenhouse plants, late-February sowings can work with sufficient warmth and bright light; outdoor crops usually benefit from a later sowing to avoid leggy seedlings. February-sown seeds catch up fast; March sowings still crop well but start picking a fortnight later.
• Pot on at first true leaves. Move seedlings into 9 cm pots once the second pair of leaves has formed (around 3–4 weeks after sowing).
• Harden off in late April to early May. Seven to ten days of leaving plants outside during the day and bringing them in at night. Skip this step and the leaves bleach white and the plants stall.
• Plant out in the greenhouse: late April (south UK) to mid-May (north UK). A heated greenhouse lets you go earlier; an unheated one needs you to wait until nights stay above about 5°C.
• Plant outdoors: late May to early June. Wait until after your last frost date — roughly late May in the south and mid-June in Scotland and the north of England. Outdoor temperatures need to be reliably above 10°C for steady growth.

For timing tied to your local conditions, the UK frost dates by region and June planting guide are useful cross-references. A 4-week head start indoors is the single biggest factor in getting ripe tomatoes outdoors in the UK. If you're weighing whether to start under cover or on a windowsill, our indoor seed-sowing guide walks through the propagator setup in more detail.

What You'll Need

• Tomato seed of UK-available varieties (see the Varieties section below).
• Seed tray or 9 cm pots with a clear lid, or a heated propagator.
• Multi-purpose compost for sowing; later, peat-free potting compost.
• 9 cm pots for pricking out; final pots or grow bags — choose a pot at least 30–45 cm across with plenty of compost, or plant two cordons in a standard growing bag.
• Canes (1.8 m) and soft twine for supporting cordons; pea netting or a wire frame for bush types outdoors.
• Liquid tomato feed — a high-potash feed such as Tomorite or a seaweed-based alternative.
• A max-min thermometer for the greenhouse — handy for spotting cold snaps before plants do.
• Fleece or horticultural fleece for late frosts outdoors, and shade netting for very hot July days in the greenhouse.

A windowsill is useful for starting seedlings, but fruiting plants usually need a brighter greenhouse or sunny outdoor position. Most gardeners I know start with four plants and end up with twelve by July. For general soil and compost basics and watering can advice you'll use day-to-day, those are the kit pages worth a read.

Step-by-Step Guide

1. Sow thinly into seed trays or small pots of multi-purpose compost. Cover with 5 mm of compost, water from below, and cover with a clear lid. Keep at 18–21°C — a heated propagator on a windowsill is ideal. Germination takes 7–14 days.
2. Prick out into 9 cm pots once the first true leaves are fully open. Handle seedlings by the leaves, not the stem — stems bruise and the plant rarely recovers.
3. Pot on into their final containers when roots fill the 9 cm pot. Grow cordons in large pots 30–45 cm wide, or two in a standard growing bag. Compact bush varieties suit large patio containers and hanging baskets; check each variety's mature size.
4. Plant cordons 60 cm apart. Push a 1.8 m cane into each pot or grow bag, then plant the seedling deep — up to the first true leaves — so it roots along the buried stem.
5. Pinch out side shoots on cordons every few days once they're 5 cm long. Side shoots are the small stems that appear in the leaf axil. Leave bush types alone; they branch naturally.
6. Train the main stem up the cane loosely with soft twine, adding a new tie every 20 cm as the plant grows.
7. Water consistently. Check the compost daily in warm weather and water thoroughly when needed to keep it evenly moist; container-grown tomatoes may need daily watering in hot conditions. Avoid fixed watering schedules — pot size, weather and plant size all affect demand.
8. Start feeding when the first truss of fruit sets — when the flowers have developed into tiny green tomatoes. Use a suitable high-potassium liquid tomato feed at the manufacturer's recommended rate, typically every 10–14 days.
9. Pinch out the growing tip of cordons in early August (south) or late July (north) once four to five trusses have set. This diverts energy into ripening existing fruit rather than producing more you won't have time to mature.
10. Harvest as fruit colours up. Pick tomatoes when they've developed full colour but are still firm — flavour peaks just before the fruit goes soft.

Common Problems

Tomato blight (Phytophthora infestans)

• Symptom: Brown-black lesions on leaves and stems, often with a pale green water-soaked margin, followed by greasy-looking brown patches on the fruit. Often strikes from late July onwards in warm, wet weather.
• Cause: The same fungal-like oomycete that causes potato blight — it blows in on the wind, then spreads in humid conditions. Outdoor tomatoes are most at risk; greenhouse crops usually escape.
• Fix: Grow cordons under cover where possible. If you grow outdoors, choose blight-resistant varieties such as 'Crimson Crush' or 'Mountain Magic'. Remove infected foliage promptly; where blight is spreading, remove affected plants and dispose of them through local council green waste rather than home compost. Choose resistant varieties, improve airflow and keep leaves as dry as possible. The RHS reports that no fungicides are currently available to UK home gardeners for tomato blight.

Blossom end rot

• Symptom: A sunken, leathery black patch on the bottom of the fruit, often on the first truss.
• Cause: Calcium deficiency inside the fruit — but almost always triggered by irregular watering, not by lack of calcium in the soil. Compost dries out, roots can't take up calcium, fruit develops the rot while still small.
• Fix: Water consistently. Mulch the surface of pots and grow bags with straw or compost to keep moisture even. Affected fruit won't recover — pick and bin them so the plant puts energy into the next truss.

Splitting fruit

• Symptom: Concentric cracks around the top of ripe tomatoes, or deep vertical splits.
• Cause: A sudden flush of water after a dry spell — the fruit swells faster than the skin can stretch.
• Fix: Pick split fruit promptly (they go mouldy fast) and steady your watering routine. Mulching the surface of pots cuts this problem in half.

Whitefly under cover

• Symptom: Tiny white insects fly up in clouds when you brush the plants. Leaves become sticky with honeydew and may go black with sooty mould.
• Cause: A common greenhouse pest that breeds year-round under glass.
• Fix: Hang yellow sticky traps at plant height from May. Introduce Encarsia formosa — a tiny parasitic wasp sold as biological control in the UK — once temperatures are above 18°C. Most gardeners find a combination of traps and the wasp clears a light infestation in three weeks.

Cold-snap stunting

• Symptom: Leaves turn purplish, growth stops, plants look as if they've been frosted even though they weren't.
• Cause: Night temperatures below about 8°C, especially in an unheated greenhouse in April or May. Tomatoes stall rather than die — they resume growth once it warms up, but you've lost two to three weeks.
• Fix: Hold off planting out until night temperatures are reliably above 8°C. Use a thermometer to confirm. Cover outdoor plants with fleece on cold nights — fleece can help with a brief cold snap but is no substitute for a frost-free growing position.

Expert Tips

• Use the deep-planting trick. Bury seedlings up to the first true leaves when potting on. The buried stem throws out extra roots, and the plant grows faster than one potted at the same depth it germinated at.
• Tap the flowers. In a greenhouse with no wind, cordons need help to pollinate. Tap the support cane once a day when the flowers are open, or run a hand gently over the trusses — vibration is enough to release the pollen.
• Water in the morning, not the evening. Evening watering in a cool August raises humidity and invites blight. Morning waterings let the plants drink before the day warms and let the compost surface dry out before night.
• Save your own seed from open-pollinated types like 'Gardeners' Delight', 'Moneymaker' or 'Tigerella'. F1 hybrids like 'Sungold' won't come true, but the heirlooms will. Ferment the seed in a little water for three days, rinse, and dry on a plate.
• Remove the bottom leaves once the first truss has set. By the time the second truss is flowering, the lowest leaves are doing little work and are usually the first to catch blight. Pinch them off at the main stem.

FAQ

When should I sow tomatoes in the UK? Sow indoor greenhouse crops from late February to mid-March at around 18–21°C. For tomatoes that will grow outdoors, late March to early April is usually a better sowing window. Adapt timing to local frost dates and available light.

Can I grow tomatoes outside in the UK? Yes, but outdoor crops are weather-dependent. Choose bush varieties bred for UK conditions — 'Red Alert', 'Tumbling Tom' or blight-resistant cordons like 'Crimson Crush'. Plant out after your last frost date, ideally in the sunniest, most sheltered spot in the garden, and accept that a wet August can wipe the lot out.

Why are the leaves on my tomato plant going yellow? Yellow leaves can be caused by ageing, overwatering, poor drainage, cold conditions or nutrient imbalance. Check the compost moisture, roots and feeding routine before adding nutrients. Yellowing between veins may indicate a deficiency, but diagnose the cause before using supplements.

Do I need to pinch out side shoots? Only on cordon (indeterminate) varieties. Bush (determinate) types branch naturally and side-shoot removal actually reduces their yield. If you're unsure which type you have, check the seed packet — cordons are usually described as "indeterminate" or "train up a cane".

How long do tomatoes take to ripen in the UK? From sowing to first ripe fruit is about 16–20 weeks, depending on variety and conditions. A February sowing in a heated greenhouse typically crops from late June; an outdoor bush in a poor summer might not fruit until mid-August. Picking green fruit in October and ripening it on a windowsill is normal practice in the UK. For more on storing the harvest once you've stripped the plants in late autumn, that's covered separately.

Varieties to Try

• 'Gardeners' Delight' — The classic UK cherry. Cordon, very reliable, sweet fruit, sets well even in cool summers. Widely available from all UK seed merchants.
• 'Sungold' F1 — An orange cherry that's become a UK favourite for its exceptional sweetness. Cordon, best under cover. Seed from Kings Seeds, Mr Fothergill's, or Suttons.
• 'Moneymaker' — A traditional UK cordon that's been grown since the 1960s. Mild flavour, reliable in poor summers, ideal for a first-time grower. Available everywhere.
• 'Tigerella' — A stripey heirloom, ready earlier than most large types (around 55 days from planting out). Cordon, with a slightly sharp flavour. Try from Real Seeds or the Heritage Seed Library.
• 'Shirley' F1 — A classic greenhouse cordon, heavy-cropping, with good disease resistance. Sold by all major UK suppliers.
• 'Tumbling Tom' — A bush type bred for hanging baskets and patio containers. Sweet cherry fruit, no training needed. Widely sold as young plants from garden centres in May.
• 'Red Alert' — A bush type for outdoor growing. Reasonable blight tolerance, fruit from late July onwards in the south. From Kings Seeds or Thompson & Morgan.

Sources & Further Reading

• RHS: Tomato growing advice — UK hardiness framing, sowing and feeding guidance, and a list of RHS-recommended varieties.
• BBC Gardeners' World: How to grow tomatoes — practical month-by-month coverage with UK variety recommendations.
• Garden Organic: Tomato factsheet — organic-leaning cultivation, common pest and disease treatment.
• ADAS / AHDB Horticulture: tomato production guides — commercial-grade UK timing, feeding and irrigation figures used as the reference for cordon and bush spacing.
• NIAB: Tomato variety trials — independent UK trials data on newer F1 varieties and blight resistance.
• Which? Gardening: tomato variety taste tests — independent UK taste and yield reviews updated annually.

Plants in this guide

Tomato

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