How to grow tomatoes from seed in the UK

Updated July 2026 · 7 min read

A packet of tomato seeds costs a couple of pounds and can give you kilos of fruit all summer. Growing from seed also opens up hundreds of varieties you'll never see in a supermarket. Here's the full journey, timed for the UK — from sowing on a windowsill to picking your first ripe tomato.

When to sow tomato seeds in the UK

• Late February – March — if you'll grow them in a greenhouse or polytunnel.
• March – early April — if they're going outside. Don't sow too early: leggy, root-bound plants waiting for warm weather do worse than younger ones planted at the right time.
• Missed the window? Garden centres sell young plants well into June — you can join the process at the planting-out step below.

Step 1: Sow indoors

Fill a small pot or seed tray with peat-free seed compost, water it, then sow seeds about 2cm apart and cover with a fine layer of compost or vermiculite. Tomatoes germinate best at 18–21°C — a bright windowsill above a radiator is ideal. Keep the compost just moist and you'll see seedlings in 7–14 days.

Step 2: Prick out into pots

Once seedlings have their first pair of "true" leaves (the serrated ones that appear after the initial rounded pair), move each into its own 7–9cm pot. Handle them by a leaf, never the stem, and bury them slightly deeper than they were — tomatoes grow new roots along any buried stem, which makes a sturdier plant.

Step 3: Pot on and keep them growing

Keep them somewhere bright and turn the pots every couple of days so they don't lean towards the light. If roots start showing at the drainage holes before it's warm enough to plant out, move them up to a slightly bigger pot. Feed weekly with a general-purpose liquid feed once they're 15cm tall.

Step 4: Harden off

UK tomatoes can't go outside until all risk of frost has passed — mid-May in the south, late May to early June further north. For 7–10 days before planting, put your plants outside during the day and bring them in at night. This "hardening off" toughens the leaves and prevents the shock that stalls unacclimatised plants.

Step 5: Plant out

Choose the sunniest, most sheltered spot you have — tomatoes want 6–8 hours of sun. Plant deeply (up to the first leaves), 45–60cm apart, in rich soil or 30cm+ pots and growbags. Push in a sturdy cane or spiral support at planting time; doing it later damages roots.

Summer care: water, feed, pinch

• Water consistently. Irregular watering is the main cause of split fruit and blossom end rot. Little and often beats drought-then-drench.
• Feed weekly with a high-potash tomato feed once the first flowers appear.
• Pinch out cordon side shoots weekly, and stop the plant (snip the growing tip) after 4–5 trusses of fruit outdoors so the plant ripens what it has.
• Remove lower leaves below the first truss as fruit develops — better airflow means less blight risk.

Harvesting

Pick fruit as soon as it's fully coloured — regular picking encourages more. At the end of the season, ripen any stubborn green tomatoes indoors in a drawer with a banana (the ethylene it releases speeds ripening), or turn them into chutney.

Common problems

• Blight — brown patches on leaves and fruit in warm, wet spells. Water at the base, keep foliage dry, and pick off affected leaves fast.
• Blossom end rot — black sunken patches on the fruit base. It's a calcium shortage caused by erratic watering, not the soil. Water more evenly.
• Yellowing leaves — often hunger or overwatering. See our guide to why leaves turn yellow.