Start seeds indoors from late January, but most wait until March

Indoor sowing in the UK starts in late January and runs until late April. The earliest sowings are slow growers that need a long season: onions, leeks, chillies and celeriac. Tomatoes, peppers and early brassicas follow from February. Fast, frost-tender crops such as courgettes, squash, sweetcorn and beans go in last, from late March, because they’d outgrow their pots if sown earlier.

Every one of these dates is counted back from the last spring frost. Put in your own date in our seed sowing planner and it lists the whole year for you, in order.

Indoor sowing dates, crop by crop

These are for a typical lowland garden in England or Wales, with a last frost around 20 April.

Crop	Sow indoors	Plant out
Onions from seed	Late January to late February	Early March to mid-April
Leeks	Late January to early March	Early April to late June
Chillies	Late January to early March	Early May to early June
Celeriac	Late January to early March	Early May to early June
Peppers and aubergines	Early February to early March	Early or mid-May to early June
Broad beans and peas	Early February to March	March to mid-April
Cabbage, cauliflower, Brussels sprouts	From early February (late January for cauliflower)	Late March or April to late June
Tomatoes	Late February to late March	Early May to early June
Lettuce	Late February to early April	Late March onwards
Kale and broccoli	From late February	Late March onwards
Basil	Early March to early May	Early May to mid-June
Courgettes, cucumbers, squash	Late March to late April	Early May to early June
Sweetcorn	Late March to late April	Early to late May
Runner and French beans	Late March to late April	Early May to early June
Pumpkins	Late March to mid-April	Late April to mid-May

Brassicas, kale and lettuce have long sowing windows, so there’s no rush. A few seeds every three or four weeks gives a steadier supply than one big sowing.

Adjusting for where you live

The table assumes a last frost around 20 April. Move every date to match your own:

• Scotland, northern England, high ground and frost pockets: last frosts often come in early or mid-May, so sow tender crops two or three weeks later than the table.
• The south-west, coasts and big cities: frosts can end in late March or early April, so you can start a week or two earlier.

If you don’t know your date, our guide to the last frost in the UK has typical dates by area.

Why earlier isn’t better

It’s tempting to sow in January to get ahead. For anything that has to wait for the last frost before going outside, it usually backfires. Seedlings sown too early run out of light, stretch, and sit in small pots for weeks. They then take longer to settle in once planted out than younger, stockier plants sown at the right time.

The exceptions are the genuinely slow crops. Onions from seed need a long season to make a good bulb, and hot chillies take months to ripen, so both benefit from a January or February start, ideally with a heated propagator and extra light.

Getting seedlings off to a good start

1. Use fresh seed compost. Garden soil and old compost carry damping-off fungus.
2. Sow at the depth on the packet, usually about twice the seed’s width. See how deep to sow seeds.
3. Keep the compost moist, not wet. Water from below where you can.
4. Give them the brightest windowsill you have, and turn the pots every day.
5. Pot on into bigger pots when the first true leaves appear.
6. Harden off for a week to ten days before planting out. How to harden off seedlings has the steps.

VegLog works out these dates from your own town’s frost dates and adds each sowing to your weekly list when it’s due.