When to Plant Tomato Seeds in the UK

Tomatoes are one of the most forgiving crops to grow from seed in the UK, but timing matters — sow too early and you'll end up with leggy, pot-bound plants stuck indoors for months; sow too late and you'll lose weeks of the ripening season.

The short answer

Sow tomato seeds indoors (on a windowsill or in a heated propagator) between late February and early April, depending on how much warmth and light you can give the seedlings before it's warm enough to plant them out.

| UK region | Sow indoors | Plant out (after last frost) | |---|---|---| | Southern England | Early–mid March | Mid–late May | | Midlands | Mid–late March | Late May–early June | | Northern England & Scotland | Late March–early April | Early–mid June |

Cordon (indeterminate) varieties grown in an unheated greenhouse can go out roughly two to three weeks earlier than outdoor plantings, since the greenhouse buffers against late frost.

Sowing indoors

1. Fill small pots or modules with seed compost, sow one or two seeds per pot at about 1cm deep, and water gently.
2. Keep at 18–21°C — a warm windowsill or heated propagator works. Germination takes 7–14 days.
3. Once seedlings have their first true leaves (not the small rounded seed leaves, but the jagged "proper" tomato leaves), pot on into 9cm pots.
4. Keep potting on into progressively larger pots as roots fill the current one — a tomato plant that's rootbound too early will stall.

Hardening off

About 10–14 days before you plan to plant out, start hardening off: put plants outside in a sheltered spot for a few hours a day, gradually increasing the time (and eventually leaving them out overnight if there's no frost risk). Skipping this step is the single most common reason transplants sulk or die after planting out — the shock of full sun, wind and cooler night temperatures all at once is hard on a plant raised entirely indoors.

! Don't rush the last-frost date. A late frost after planting out can kill young tomato plants outright — if in doubt, wait an extra week rather than risk it, especially in the Midlands, North and Scotland where late frosts are more common.

Outdoor vs greenhouse

Outdoor tomatoes (usually bush/determinate varieties) are lower-maintenance but ripen later and are more exposed to UK weather — blight is a real risk in a wet summer. Greenhouse or polytunnel-grown cordon tomatoes ripen earlier, crop for longer, and are much less prone to blight, but need regular side-shoot removal and tying in as they grow.

Quick reference

• Sow indoors: late Feb–early April (region-dependent)
• Pot on: as soon as roots fill the current pot, usually every 3–4 weeks
• Harden off: 10–14 days before planting out
• Plant out: only after your local last-frost date has passed

Once you know your sowing dates, browse seeds and greenhouse gear compared across UK retailers on GrowMuir — and see our guide to what else to sow this month for the rest of your growing calendar.