When to plant tomatoes in the UK splits into two jobs that people often muddle together. Sow the seed indoors between late February and early April, then plant out from mid May in a greenhouse and from late May into early June outdoors, once the frosts have finished. Sow too early and you spend April nursing pale, stretched seedlings that never recover. Plant out too early and one cold night undoes months of work. The dates below are the ones I use in Oxfordshire, with adjustments for wherever you garden.

Why Tomatoes Punish an Early Start

The urge to sow tomatoes in January is almost irresistible. The seed packets are sitting there, the catalogues have been arriving since Boxing Day, and sowing something feels like the season finally starting. I have given in to it more than once and it has never once paid off.

The problem is not germination. Tomato seed will come up happily in February on a warm windowsill. The problem is what happens next. A seedling needs strong light to build a stocky plant, and in February and early March there simply is not enough of it in a British house. The plant stretches towards the window, the stem goes thin and pale, and by the time it is warm enough to go outside in late May you are holding a leggy, exhausted thing that has been living in a pot for four months. A plant sown in late March, into brightening days, will overtake it within a fortnight of planting out and crop earlier. That is not a theory, it is the same lesson I have relearned in three separate years.

Then there is the frost. Tomatoes are killed outright by it, not merely checked, and even a cold night at three or four degrees with no frost at all will stall a young plant for a fortnight. Every date on this page exists to keep your plants away from those two problems.

Sowing Tomato Seeds Indoors

Late February to early April is the window, and where you land inside it depends on where the plants are going. If you have a heated greenhouse, sow from late February. For an unheated greenhouse, mid to late March. For outdoor tomatoes, late March into early April is plenty, and I would rather sow in the first week of April than the first week of March.

Tomato seed germinates best between about 18C and 24C, which is warmer than most rooms. A seed tray with a propagator lid holds that warmth and humidity steadily, and it is the difference between patchy germination and a full tray. An airing cupboard works too, as long as you check daily and move them to the light the moment the first shoot appears. Leave them in the dark a day too long and they stretch beyond saving.

Variety matters more than most beginners expect. Cherry types are far more forgiving of a British summer than big beefsteaks, which often run out of season before they ripen. Sweet Million tomato seeds are a good starting point, heavy cropping and reliable, and a plant or two will keep a household in cherry tomatoes from July. If you want the fuller picture on varieties and growing method, that sits in my guide to growing tomatoes in the UK, and the RHS tomato guide is a good second opinion on sowing depth.

Potting On and Keeping Plants Stocky

Once seedlings have their first pair of true leaves, move them into individual pots. Tomatoes are unusual here and it is worth knowing: you can bury the stem right up to the lowest leaves and the buried section will grow roots. That is the single best trick for rescuing a seedling that has already gone a bit leggy, and it is why tomatoes forgive that mistake when most crops do not.

After that the job is light and cool rather than warm and dim. A slightly cooler, very bright spot produces a short, thick-stemmed plant. A warm dark corner produces a tall weak one. If your only window faces north, a sheet of kitchen foil propped behind the tray bounces a surprising amount of light back and stops the plants leaning so hard. Turn the pots every couple of days as well. If yours have already gone tall and floppy, why tomato seedlings go leggy covers how to bring them back.

Greenhouse or Outdoors Changes Everything

A greenhouse buys you roughly two to three weeks at each end of the season, and in a British summer that is the difference between a decent crop and a glut. Greenhouse plants can go into their final position from mid May in most years, or early May with fleece to hand. They also stay dry, which matters enormously because blight arrives on warm wet weather and wet leaves are how it takes hold.

Outdoor tomatoes wait for the frosts to finish properly, which for most of the country means the last week of May into the first week of June. If you have left it later than that, it is worth checking whether it is too late to plant tomatoes. They want the warmest, most sheltered spot you have, ideally against a south-facing wall that holds heat overnight. Grow a blight-resistant variety outdoors if you can, because in a wet August an ordinary outdoor tomato is at the mercy of the weather. If you are unsure when your own frosts finish, the last frost date checker will give you a date for your postcode rather than a national average.

Soil Temperature, the Thing Nobody Checks

Air temperature is what everyone watches, and soil temperature is what actually decides whether a newly planted tomato gets going. You want soil at about 12C or above before planting out. Cold soil in May is why plants sit there doing nothing for three weeks after an apparently perfect planting day.

Warming the bed is easy and worth the effort. A sheet of black plastic or a couple of cloches over the planting area for a fortnight beforehand lifts the soil temperature noticeably. Wet soil is the other half of the problem, since waterlogged ground stays cold and rots roots, so if your ground sits wet it is worth improving the drainage or planting into raised beds and pots instead. Working plenty of compost into the soil the autumn before does both jobs at once.

Month by Month

February

Only sow now if you have a heated greenhouse to move plants into. Otherwise use the month to order seed and clean pots, and leave the sowing alone.

March

The main sowing month for greenhouse tomatoes, and a good time to start outdoor ones in the north where the season runs late. Sow indoors in warmth, then get the seedlings into strong light immediately.

April

The last sensible sowing window for outdoor plants, and the month for potting on. Towards the end of April, greenhouse plants can start moving into their final positions if the weather is kind. Do not be tempted to put anything outside yet.

May

The month everything happens, and the month that catches people out. Greenhouse tomatoes go in from mid May. Outdoor plants get hardened off across the last two weeks and planted out at the very end of the month at the earliest. Watch the forecast rather than the calendar, because a warm week in early May means nothing about the nights that follow it. There is more on the wider May jobs in what to plant in May.

June

The safe month for outdoor planting everywhere in the UK, and not late at all. Plants going out in the first half of June will crop perfectly well. Early June is also when you start tying in and pinching out side shoots, which is covered in June gardening jobs.

Where You Live Changes the Dates

Everything above is written for the middle of England. In the South West and along the south coast, mild winters and early springs mean you can usually plant out a week or two earlier, and outdoor tomatoes are genuinely reliable. London and the South East run similarly early, with the added help of the heat that cities hold overnight.

Across the Midlands the standard dates apply as written. In northern England, push planting out into early June and lean towards a greenhouse or a very sheltered wall. In Scotland, outdoor tomatoes are hard work outside the mildest coastal spots, so a greenhouse or polytunnel is close to essential, and planting out before the middle of June is asking for trouble. Altitude and local shelter matter as much as latitude, and a neighbour who has gardened the same street for twenty years is a better guide than any map.

Hardening Off Properly

This is the step people skip when they are impatient, and it is the one that costs them. A tomato raised indoors has soft growth and no defences against wind or direct sun, and moving it straight outside scorches the leaves and shocks the plant badly.

Give it a fortnight. Start with an hour or two outside in a sheltered spot, build up over the days, and bring the plants in every night for the first week. In the second week they can stay out overnight if there is no frost forecast. I lost most of a batch years ago by doing this over a single sunny weekend, and the plants that survived cropped weeks behind the ones I did properly the following year. The full hardening off method applies to every tender crop, not just tomatoes.

Planting Out: Depth, Spacing and Support

Choose a mild overcast day rather than a hot bright one, and water the plants an hour beforehand. Plant deep, burying the stem up to the first leaves as you did when potting on, because those buried roots make a sturdier and more drought-resistant plant.

Give them room. Cordon tomatoes want about 45cm between plants, bush types more like 60cm, and greenhouse rows want 45 to 60cm with space to walk. Crowding is a false economy: airflow drops, humidity rises, and you invite exactly the fungal problems described in tomato diseases in the UK. Put the support in on planting day rather than later, since driving a cane in beside an established plant tears through the roots. Tomato canes or plant stakes do the job for cordons, and a truss of fruit is heavier than people expect.

The Mistakes That Cost a Crop

Four things account for most tomato disappointment, and all of them are about timing rather than skill. Sowing in February and keeping plants indoors for four months. Planting out during a warm spell in early May, then losing them to a cold night ten days later. Rushing the hardening off. And planting into cold, wet soil that has not warmed through, which stalls a plant for weeks and can rot it outright.

Notice that none of those is about feeding, pruning or watering. Those matter later, but they cannot rescue a plant that started badly. If your plants are already in and misbehaving, work through common tomato problems, and if they are flowering without setting fruit, tomato plants not producing fruit covers that specifically.

Tomatoes in Pots and Raised Beds

Containers give you a genuine timing advantage because compost warms faster than open ground, and pots can be moved into shelter or dragged against a wall when a cold night threatens. On a patio you can often plant a week or so earlier than in a bed.

Go large. One plant per 30cm pot at the very least, and bigger is better. The small pots people use are the reason so many container tomatoes wilt daily and suffer blossom end rot, since erratic watering stops the plant taking up calcium. Raised beds sit neatly in between, warming earlier than open ground while holding moisture better than a pot. Whichever you choose, consistency of watering matters more than the container itself.

When Your Tomatoes Will Be Ready

Count roughly 16 to 20 weeks from sowing to the first ripe fruit. In practice, a March sowing planted out in late May gives greenhouse tomatoes from mid July and outdoor ones from late July or early August, running on until the first frosts.

Planting date shifts that whole window. Greenhouse plants in by mid May can be picking in early July. Standard late May planting brings the main crop through August and September. A late June planting still crops, but everything arrives in September when the light is going, and you will finish the season with more green fruit than red. That is not a disaster, since green tomatoes make excellent chutney, but it is worth knowing before you decide to delay.

Helping Them Ripen Before the Season Ends

By late August, stop the plants. Pinch out the growing tip two leaves above the top truss so the plant stops making new growth and puts everything into the fruit it already carries. Remove the lower leaves to let light and air at the trusses, and cut back on watering slightly, which concentrates flavour.

If frost is forecast and there is still green fruit outside, pick everything and bring it in. A banana in the bowl or the bag speeds it along, and any that refuse to turn go in the chutney pan. BBC Gardeners’ World has more on end-of-season care if you want another view.

Quick Reference

• Sow indoors: late February (heated greenhouse) to early April (outdoor plants)
• Pot on: when the first true leaves appear, burying the stem deep
• Harden off: two weeks before planting out
• Plant in a greenhouse: mid May onwards
• Plant outdoors: late May to early June, after the last frost
• Soil temperature: about 12C or warmer before planting out
• First ripe fruit: roughly 16 to 20 weeks from sowing

If you are planning the rest of the plot around these dates, the full vegetable planting calendar puts tomatoes alongside everything else going in through spring.

When to Plant Tomatoes in the UK: Frequently Asked Questions

A Sensible Place to Start

If all of this feels like a lot to hold in your head, reduce it to two decisions. Sow in late March. Plant out at the end of May. Those two dates will serve you well almost anywhere in the UK, and everything else on this page is refinement around them.

Then be later than feels right. Every gardener I know, myself very much included, has lost plants to impatience and none of us has ever lost one to waiting an extra fortnight. The plants catch up faster than you think, and a tomato that goes into warm soil and settled weather will overtake one that was rushed and checked. Grow two or three plants properly rather than eight badly, and you will get more tomatoes with less worry.