UK Sowing Guide by Month

January

The quietest sowing month of the year. Outdoors, cold wet soil means almost nothing germinates, so the real work is planning: order seed now while every variety is still in stock. With a heated propagator you can start chillies and peppers indoors, since both need the longest season you can give them. In mild southern gardens, broad beans can go in under cloches. Harvest carries on regardless, with parsnips, leeks, winter brassicas all standing happily in the ground.

February

Still winter, but the indoor season starts properly. Sow tomatoes, peppers, chillies in a heated propagator or on a warm windowsill; they need the head start. Broad beans can be sown outdoors in mild areas under cloches, or in pots in a cold frame elsewhere. Garlic goes in now if you missed the autumn slot, as it still gets enough cold to split into cloves. Outdoors, leave the soil alone until it stops sticking to your boots.

March

The outdoor season opens. Once soil holds 10°C, direct-sow peas, carrots, spinach, radishes, rocket, spring onions, parsnips. Indoors, keep the tomatoes going and start brassicas such as cabbage and broccoli in modules. Onion sets can be planted, and first early seed potatoes go in from late March in milder areas. Frost is still a regular visitor, so hold tender crops back and keep fleece to hand for anything already up.

April

The busiest sowing month on the calendar. Direct-sow beetroot, radishes, lettuce, chard, kale, carrots outdoors. Indoors, start courgettes, squash, pumpkins, sweetcorn in pots, with French and runner beans towards the end of the month. First early potatoes should be in by now; maincrops follow mid-month. April frosts catch people out every year, so nothing tender goes outside yet. A soil thermometer settles any argument about whether a bed is ready.

May

The month the frost risk ends across much of the UK, typically mid to late May and later in the north. Once soil reaches about 12°C, direct-sow French beans and runner beans. Sweetcorn is fussier: it wants soil nearer 15°C to germinate reliably outdoors, so start it in pots in May and plant it out, or hold the direct sowing back until the warmth arrives, usually June. Plant out tomatoes, courgettes and squash once your last frost date has passed, and check that date for your postcode with the frost date calculator rather than guessing. Keep sowing salad leaves every couple of weeks so the picking never stops.

June

Sowing carries on while planting out takes over. Direct-sow beetroot, carrots, lettuce, turnips for autumn eating. Plant out leeks, celeriac, sweetcorn. Get the last tender plants in early in the month. The first proper harvests arrive too: broad beans, peas, salad leaves, the first strawberries. Watering becomes the job that decides everything from here, above all for anything newly transplanted into summer soil.

July

Peak harvest month, but the sowing year is far from over. Direct-sow beetroot, carrots, radishes, rocket, spring onions, turnips now and they crop through autumn. Keep sowing lettuce in a lightly shaded spot, as summer heat makes it bolt in full sun. Plant out the last leeks. Anything sown this month races out of the ground in warm soil, which makes July sowings some of the easiest of the year.

August

Radishes, rocket, turnips and lettuce can still be sown outdoors in August, and the RHS lists them as August sowings for the south of England.^RHS Hardy spinach goes in now for autumn picking,^RHS salad onions are sown little and often right through to autumn,^RHS and early August is the RHS window for lettuce that crops in early winter under cloches.^RHS Further north the same crops still work where the weeks to harvest fit before your first frost. What decides it is not the date but whether the crop's weeks to harvest fit inside the weeks left before your first autumn frost, which varies by more than six weeks between regions. A crop that takes four weeks has a completely different late-summer deadline to one that takes ten. Get that comparison right and “is it too late?” stops being a guess; the frost date calculator gives you the date to count back from.

The maths: count back from your frost date

UK first frost dates vary far more by region than most sowing advice admits. Using Met Office HadUK-Grid 5 km gridded observations (1991–2020), the first autumn frost typically arrives from late October in the Scottish Highlands, from mid-November to early December across most of England and Wales, and in December or later in mild south-western coastal areas such as Cornwall.^{Met Office data}

Counting forward from 15 August gives a spread of ten weeks or more between regions:

Those week counts are simple calendar arithmetic from the published frost ranges, not a promise for your garden. Frost dates are a distribution rather than a fixed line, and a frost pocket, valley bottom or exposed plot can shift the real date. GardenCalc's postcode estimate covers 2,728 UK postcode districts.^{Met Office data}

What still fits after 15 August

Cross-referencing each crop's typical time to harvest against the frost windows above gives this late-summer shortlist:^{RHS crop guides}

The sowing windows and harvest times come from GardenCalc's planting calendar, cross-checked against the Royal Horticultural Society's grow-your-own vegetable guides.

What's genuinely too late

The blanket “too late to sow” advice is wrong for the fast crops above, but it is right for the slow ones. From seed in mid-August, these are past their window almost everywhere in the UK:^{RHS crop guides}

• Outdoor tomatoes — need to be planted out after the last frost in spring to ripen before autumn cold
• Sweetcorn — needs a full summer of heat; a mid-August sowing will not cob before frost
• Runner beans — need around 12 weeks plus warm soil and warm nights; declining temperatures arrive before reliable pod-set
• Maincrop potatoes — are planted from seed potatoes in spring, not sown from seed in summer

Two things that cost more yield than the date does

Spacing: Warm August soil germinates quickly, which makes it easy to sow too thickly out of spring habit. Thin seedlings once they are large enough to handle, following the spacing on the seed packet, so rows do not bolt or stay undersized.^RHS

Slug pressure: Young late-summer seedlings are easy targets. Protect new sowings from day one with a physical barrier such as a cloche or another wildlife-conscious control, rather than waiting for damage. Winter lettuce and spinach are particularly vulnerable while small.^RHS

September

The last real outdoor sowing month. Winter spinach, lamb's lettuce and winter lettuce go in now for picking through autumn and again in spring. Radishes and rocket still fit in the first half of the month in milder areas. Towards the end of September you can start planting garlic, though October is its main month. Everything else waits for spring, so clear finished crops and get compost onto empty beds while the soil is still warm.

October

Garlic's month. Plant cloves now so they get the winter cold that makes a bulb split properly rather than growing as one round. Overwintering broad beans go in towards the end of the month in mild areas. Winter lettuce can still be sown under cloches. Beyond that, October is for clearing beds, mulching, planting spring bulbs, with the first frosts arriving in northern and inland gardens before the month is out.

November

Last calls. Garlic can still go in, and overwintering broad beans are worth a try in mild southern gardens, though they are a gamble further north. Otherwise the sowing year is done. Mulch empty beds, clean pots and tools, and check stored crops for rot. It is also the best month to look back at what worked while it is still fresh, and adjust next year's plan accordingly.

December

Nothing goes in the ground this month, and that is fine. Harvest carries on with parsnips, leeks, kale, Brussels sprouts, all of which stand through frost. The one job that pays all year is done from an armchair: order seed for the new season before the popular varieties sell out, and sketch out the beds month by month using the planting calendar.