What to Sow Indoors in March — UK

These crops all need a protected, warm start. A heated propagator at 18–21°C is ideal; a warm windowsill works for hardier types. According to the RHS March growing guide, soil temperatures below 10°C will stall germination for most tender crops.

• Tomatoes — sowing now gives the essential 6–8 weeks of protected growth before the final frosts pass in May. Check when to plant tomatoes UK for regional timing, then follow our full how to grow tomatoes UK guide once they’re in the propagator.
• Aubergines — need a long, warm growing season; a March start in a heated propagator is non-negotiable.
• Peppers (Sweet & Chilli) — March is your last realistic window if you want mature, ripening fruit before autumn light fades.
• Celeriac — this slow-growing root requires a massive head start to reach harvestable size by October.
• Celery — sowing early in modules ensures strong, robust seedlings ready for planting out once soil reliably warms.
• Cucumbers (Greenhouse) — starting indoors now means vigorous plants ready to transfer to the greenhouse border in late spring.
• Brussels Sprouts — an early indoor sowing gives these brassicas the long, steady growing season they require for a solid winter harvest.
• Leeks — sowing in deep pots now produces sturdy, pencil-thick transplants for early summer planting. Once they reach pencil thickness, learn how to grow and dibble leeks for long, blanched stems.
• Summer Cabbage — an early start in modules provides a valuable early summer cut before maincrop varieties mature.

What to Plant Outdoors in March (South UK Only, Under Fleece)

Average UK soil temperature in March sits at just 5–7°C. Only the hardiest crops go in outdoors — and only in southern England, under fleece or cloches to warm the soil first.

• Broad Beans — hardy seeds sown directly to establish strong root systems before blackfly season peaks. March is the traditional time to sow hardy broad beans directly into the soil.
• Peas (Hardy round-seeded) — fleece warms the soil just enough to trigger germination without seeds rotting in cold, wet ground. If your peas fail to sprout, cold soil temperature is almost always the cause — see our guide to why seeds don’t germinate in the UK for fixes.
• Radishes — fast-growing and cold-tolerant; one of the quickest returns from a March outdoor sowing.
• Spinach — thrives in cooler days of early spring and resists bolting far better than late-spring sowings.
• Early Carrots — sowing under fleece protects seedlings from late frosts and gives a head start against the first wave of carrot root fly. Know exactly when to plant carrots to outpace that first generation.
• Spring Onions — early varieties under cloches provide an early summer harvest to bridge the gap before maincrop onions are ready.

What to Harvest in March — The Hungry Gap Crops

March is the heart of the hungry gap. These overwintered crops are your bridge between winter stores and the first spring harvests.

• Purple Sprouting Broccoli — the star of the hungry gap, providing sweet, tender shoots precisely when other fresh harvests are scarce.
• Leeks — late-season varieties are now at their peak, standing perfectly in cold ground until you need to lift them.
• Parsnips — winter frosts have converted their starches to sugars, making March-harvested parsnips the sweetest of the year. The Soil Association recommends leaving parsnips in the ground until after the first hard frosts for maximum sweetness.
• Kale — overwintered plants produce a final flush of tender side shoots before bolting to seed.
• Swiss Chard — established plants put on fresh, vibrant growth as days lengthen, offering excellent early spring greens.

5 March Tasks That Determine Your Summer Harvest

1. Get tomatoes, peppers, and aubergines into a heated propagator by mid-March — these crops need 6–8 weeks of protected growth before outdoor planting. Every week lost now is a week lost at harvest.
2. Warm outdoor soil with cloches or fleece before sowing — two weeks of cloche cover can raise soil temperature by 3–4°C, making the difference between seeds germinating and rotting.
3. Start chitting maincrop potatoes in early March — place in a cool, light, frost-free spot so they develop sturdy, dark green shoots ready for April planting.
4. Top-dress overwintered brassicas with blood, fish, and bone — purple sprouting broccoli and kale need a nitrogen boost now to fuel their intensive spring growth spurt.
5. Plan your succession sowing schedule — sow in small batches every 2–3 weeks rather than all at once. This prevents a glut of seedlings and spreads your harvest across the season.