Cool-Season vs Warm-Season Crops
Vegetables respond very differently to British temperatures. Cool-season crops keep growing in chilly spring and autumn weather, while warm-season crops need warmth and protection from frost. Understanding the difference helps you plan sowing, use space efficiently and avoid the common disappointment of planting tender vegetables outside too early.
Sort your seed packets into two working groups before the season starts. Cool-season vegetables include peas, broad beans, brassicas, salads, spinach, rocket, radish, beetroot, onions and leeks. They tolerate cool weather and many can be sown early or late in the year. Warm-season vegetables include tomatoes, courgettes, French beans, runner beans, sweetcorn, cucumbers, peppers, chillies and aubergines. These grow best when both soil and nights are warm, and frost can kill them. Keep the labels, because varieties differ in maturity and hardiness. Make a rough garden plan showing which beds will be free in spring and which will become available after an early cool-season crop has finished.
Prepare a cool-season bed from late winter onwards when soil is workable. Weed it, spread garden compost and rake a fine surface for small seed. In February or March, sow broad beans in modules under cover or directly outside in milder districts. From March, sow short rows of peas, salads, spinach, rocket and radish, with later sowings every few weeks. Plant hardy brassica seedlings from April when they have been hardened off. Use fleece during sharp cold spells and net brassicas against pigeons. Cool-season crops still need light and air movement, so avoid keeping covers closed constantly. Water seedlings carefully, then thin them early to give each plant enough room to develop.
Treat warm-season crops as indoor or protected crops until late spring. Sow tomatoes, courgettes, cucumbers, sweetcorn and French beans in peat-free multipurpose compost from April, using module trays or individual pots. Provide bright light and moderate warmth, but do not overwater small seedlings. Runner beans can be started in May or direct-sown after frost risk has passed. Before outdoor planting, harden plants off for seven to ten days by exposing them to outside conditions gradually. In most gardens, plant tender crops from late May or June, later in frosty valleys and cooler parts of Scotland. A greenhouse, polytunnel or warm sheltered wall can extend the season, but ventilation remains important.
Use your local last spring frost as the dividing line, while recognising that sites vary. A sheltered coastal garden may be ready earlier than an inland allotment, and cold air settles in hollows. Check forecasts from April onwards and keep fleece available for vulnerable plants. If a warm-season crop is planted out too soon, cold soil may stop growth even without a visible frost. It is usually better to wait a week than nurse damaged plants for months. Conversely, cool-season crops can bolt or become bitter when heat arrives, so sow them in partial shade during summer and keep moisture steady. Shade from taller crops can help lettuces and spinach in warm spells.
Plan succession so cool- and warm-season crops share a bed across the year. Harvest spring radishes, rocket, spinach or early peas, then prepare the cleared space for courgettes, beans or sweetcorn after late May. In late summer, remove spent warm-season plants and sow rocket, spinach, winter salads or broad beans where conditions allow. Add compost between crops, but avoid leaving bare soil for long. Tall warm-season crops can cast useful shade, though they must not block lower crops completely. Keep crop families rotating where space permits: follow peas and beans with brassicas or salads, for example, rather than repeating the same family in one place year after year.
Respond to the weather instead of relying solely on a calendar. Cool, wet springs favour slugs and slow germination, so use modules for vulnerable crops and inspect plants regularly. Hot, dry periods make salads bolt and cause beans or courgettes to suffer if watered irregularly. Mulch established plants with garden compost or clean grass clippings, keeping mulch away from stems. Water the soil deeply in the morning or evening rather than wetting leaves repeatedly. Record when each crop was sown, planted and harvested, plus notable frosts or heatwaves. After one or two seasons, these notes will show which dates work best for your particular garden or allotment.
Frequently asked questions
Can cool-season vegetables survive a frost?
Many can tolerate a light frost, particularly peas, broad beans, kale, cabbage and hardy salads. Young plants are less resilient than established ones, and repeated freezing winds can still damage leaves. Fleece offers useful temporary protection. Check variety labels, because not every brassica or salad has the same degree of hardiness.
When should warm-season crops go outside?
Plant them outside only after the risk of frost has generally passed and the soil has begun to warm, commonly from late May or June. Harden plants off first for seven to ten days. In cooler regions or frosty gardens, delay planting or use a greenhouse, polytunnel, cloche or sheltered position.
Can I grow tomatoes beside brassicas?
Yes, provided both crops receive suitable light, spacing and water. Tomatoes need the sunniest, warmest place, while brassicas tolerate cooler conditions. Avoid crowding them, as poor airflow increases problems. Planning crops by temperature needs is generally more important for a small garden than trying to follow every traditional companion-planting rule.
General guidance for UK home gardens and allotments. Conditions vary by region, soil and season; the RHS or a local garden centre can give site-specific advice. Page updated 19 Sep 2026.