When To Sow Tomato Seed UK

Knowing when to sow tomato seed will help produce the best crop possible and avoid many of the issues caused by low light levels and temperatures that are too low for growing seedlings.

If you intend to grow tomatoes outdoors, the best time to sow tomatoes UK (indoors), is eight to ten weeks before your estimated last frost date. Tomato seed needs to be sown indoors in warm conditions in order to germinate.

Tomato seeds - sowing times

For example, If your last frost is expected around the end of May, you would sow (indoors) from the middle to the end of March. Your seedlings would then be ready to be planted outside around the end of May, beginning of June.

You can sow up until the end of April in the UK and still expect a crop by the end of the season if you choose a quick or early maturing variety.

When to Sow Tomato Seed - Timeline for growing tomatoes in the UK

What happens if I sow seeds too early?

Sowing seeds too early (such as in January and most of February when there is not enough light) will result in leggy, weak plants that will produce fewer tomatoes later in the season!

The seedlings in the photo below (Red Alert) are becoming too leggy or spindly. This is caused by not enough light and a little too much water. The pale colour of their leaves also indicates that they aren’t getting enough light.

Leggy tomato seedlings - sow too early and they become leggy.
Leggy seedlings searching for light.

When To Sow for Growing In Unheated Greenhouse

If you intend to grow tomatoes in an unheated greenhouse, you could sow indoors at the end of February. You will need a light position or (grow light) and enough room indoors to germinate the seedlings in the warm. They could then be put out in the greenhouse early May.

How To Sow Tomato Seeds

If you are looking for tips on how to sow tomato seeds please click here.

Sowing at the right depth and keeping the seeds at the right temperature and humidity will get the best results. A propagator is also a good item to have but not essential.

Grow Lights

Seeds may be sown in February if a grow light is used to provide more light for the seedlings. Without extra light, seedlings can become very leggy (too tall with thin stems) and not be able to support the weight of their own leaves.

The benefit of using a grow light is that you can sow early and pick ripe tomatoes early too!

Here’s a link to more information about led grow lights.


Knowing when to sow tomato seed is important In order to be successful.

Start too soon and plants will be subject to conditions that are too cold and days that are too short with not enough light – unless you use a grow light of course!

It is often the case that a plant grown in good conditions a little later in the season, will overtake a plant grown earlier in the season when conditions are not as favorable.

For tips on how to grow tomatoes from seed please follow the link.

Sow seed too late and the season will end before the tomatoes have had time to ripen – especially in a short season area such as the whole of the UK!

Summary and Tips for When To Sow

  • Sowing Period UK
    Sow seed indoors around the middle of March to the end of April if you intend to grow your tomatoes outside. For growing in a cold greenhouse, seeds may be sown at the end of February – indoors of course!
  • Avoid Frost
    You cannot leave seedlings or young plants outside overnight until all danger of frost is past, which in most areas of the UK is estimated to be around mid to late May.
  • Later In The Season
    If you have missed the “sow by date” altogether, you could buy a few plug plants or pot ready plants from a garden center or order them online. Buying plug plants is much less time consuming but the choice of varieties is less than when starting from seed – there is a huge range of tomato seeds available!

Try Not To Sow Too Early!

It is very easy to be tempted to start too early – I get the urge myself to sow in February rather than March but the results will always be better when sowing in March. The best time for sowing, I think, is the last two weeks of March.

With such a small window of opportunity, getting the timing right – knowing when to sow tomato seed – is crucial for success, especially in short season areas, otherwise the results will be disappointing.

Sowing Directly In Garden Soil

Some people ask why seeds cannot be sown directly in the garden soil…?

  • Small tomato seedlings will be eaten by slugs and snails, and other little critters, within hours of germination!
  • Night temperatures outside will probably be too low and the soil itself will not be suitable for germination and young seedling growth.
  • It is best to sow seeds in new seed compost or other growing media such as coir pellets. This ensures the best chance of germination and a disease free start for the young seedlings.

Blight free tomato seeds available from Suttons.

See Also:
How To Grow Tomatoes From Seed
Tips For Tomato Seedlings
Feeding Tomato Seedlings