Earlier springs, a midsummer gap and a longer autumn: how to adjust your sowing

The sowing calendar in a seed catalogue is built on average conditions from the past. Those averages have moved. The growing season in central England was 29 days longer in 2006 to 2015 than in 1961 to 1990, according to the Met Office, and across the UK air frosts were about 17% less frequent.

That does not mean you can sow everything a month earlier. It means the edges of the season have more room, and the middle has more heat.

Spring: earlier, but not reckless

Spring arrives sooner on average, and the soil warms earlier. Hardy crops such as broad beans, peas, carrots and spinach can go in a week or two earlier than the old dates, provided the soil is workable and has reached about 7°C.

Tender crops are a different matter. Beans, courgettes, sweetcorn and tomatoes need soil around 12 to 15°C, and they are killed by a late frost. A warm March does not rule out a frost in May. Keep fleece or cloches ready, and do not put everything out on the first warm day.

The limit is often light, not temperature. Sowing in February gives a plant less daylight than sowing in March, so it grows slowly and may catch up with a later sowing anyway.

Midsummer: the gap

The longer season has a hole in the middle. July and August are hotter and drier, and that is when lettuce, spinach and coriander bolt. The crops that do well in spring struggle in the middle of summer.

Plan for the gap:

• sow lettuce and spinach in light shade, or wait until late August
• grow chard, kale and root crops through the hot months
• keep salad in a cooler corner, and water it deeply
• use shade netting over the most heat-sensitive crops

The heatwave guide covers the practical steps. Why lettuce bolts explains the trigger.

Autumn: the second season

The first frost is later than it used to be, which gives autumn sowings more time. Spinach, winter lettuce, oriental greens and overwintering broad beans can go in later than the old calendar suggests.

The risk moves to the other end. A mild autumn can keep plants growing when they should be hardening off, and a sudden cold snap in December does more damage to soft growth than to a plant that has slowed down naturally. Stop feeding in late summer, and choose hardy varieties for overwintering.

Winter: wetter, not colder

Winter rainfall is projected to rise, with more of it arriving in heavy bursts. The problem for a veg plot is drainage, not cold.

Raised beds, a rough surface, and not walking on wet soil all help. Cover empty beds with mulch or a green manure to stop nutrients washing out. Green manure for winter has the options.

What shifts, in one table

Season	What changes	What to do
Early spring	Warmer, earlier	Sow hardy crops a week or two earlier; keep fleece for late frosts
Late spring	Warmer, but frost still possible	Wait for soil temperature, not the calendar
Midsummer	Hotter and drier	Shade salad; grow roots and chard; accept a gap
Early autumn	Still warm	Sow late salad and overwintering crops
Late autumn	First frost later	Leave hardy crops in longer; watch for wet soil
Winter	Wetter	Improve drainage; mulch; stay off wet beds

The number that still rules

Your own last frost date is still the most useful date in the garden. A national average hides the difference between a sheltered coastal plot and a frost pocket in a valley. If you know your last frost, you can shift the rest of the calendar around it.

VegLog works sowing dates from your own frost dates, so the charts move with your garden rather than a national average.

For the wider picture, see growing vegetables in a changing climate. For the tools, the seed sowing date calculator and the crop pages use the same frost model.