You can start spring gardening in earnest from March, when days lengthen and soil begins to warm. In the south of England, some crops like broad beans and onion sets can go out in late February. In Scotland and northern England, the outdoor sowing season typically starts in April. Indoors, seed sowing for tender crops like tomatoes and peppers begins in late February or March regardless of region.

The average last frost date is mid-April in southern England, late April to early May in the Midlands and Wales, early to mid-May in northern England, and mid-to-late May in Scotland. Tender crops — tomatoes, courgettes, beans, sweetcorn — should not be planted outside until after your local last frost date.

Start with hardy crops that tolerate cold: broad beans, peas, onion sets, garlic, and shallots can go outside from March. Indoors, begin tomatoes, peppers, and leeks in late February or March. Lettuce and spinach can be sown outdoors under fleece from March. Radishes are the fastest reward — ready in 4 weeks from a March sowing.

Keep horticultural fleece to hand through May and cover tender plants if frost is forecast. Cloches and cold frames provide more substantial protection. Harden off indoor-raised seedlings gradually before planting out — sudden exposure to cold kills more plants than frost itself. Check the forecast nightly in April and May.

The most common cause is soil that is too cold. Most vegetable seeds need a minimum of 7°C to germinate; tender crops need 10–15°C. If you've sown outdoors too early, seeds will sit dormant or rot in cold, wet soil. Use a soil thermometer, wait for the right temperature, or start seeds indoors in a propagator and transplant once conditions improve.