What to Plant in March in the UK

March is the month UK gardeners have been waiting for. After weeks of cold grey, the soil is starting to warm, the days are lengthening, and there is finally a reason to get your hands dirty again. But late frosts can still catch you out through to May, and planting the wrong thing at the wrong time can cost you a whole season's work overnight.

This guide covers exactly what to plant in March in the UK — indoors, under cover, and outside — with timing notes, soil temperature guidance, and the crops you should hold off on for another 6–8 weeks.

What to Sow Indoors in March

Indoor sowing in March is where most of the early-season action happens. A heated propagator (or a warm, bright windowsill) lets you start crops that need a long growing season well before the soil outside is ready.

Vegetables to Start Indoors in March

• Tomatoes — Sow in a propagator at 18–25°C from mid-March. They need 6–8 weeks indoors before transplanting; a 15 March sow means planting out around mid-May.
• Peppers and chillies — These need sustained heat. A propagator set to 21°C or above is ideal. Sow as early in March as possible — they are slow growers.
• Aubergines — Same conditions as peppers. Long season required. Sow early March at the latest.
• Celery and celeriac — Sow indoors from early March. Do not cover the seeds — they need light to germinate.
• Leeks — Sow in trays indoors from early March, transplant outdoors in May or June.
• Onions from seed — Sow indoors in early March in trays, or buy sets and plant those directly in late March.
• Cauliflower and broccoli — Start indoors in March for a summer harvest.

Herbs to Start Indoors in March

• Basil — Needs warmth (18°C+). Sow on a warm windowsill or in a propagator. Not outdoor-ready until June.
• Parsley — Slow to germinate (3–4 weeks). Sow indoors in March for a May transplant.
• Coriander — Use bolt-resistant varieties. Sow small batches every 3–4 weeks to avoid a glut.

What to Sow Directly Outdoors in March

From mid-to-late March, you can begin direct sowing outdoors — provided your soil has reached at least 7°C and you are ready to cover with fleece if frost threatens.

Flowers to Plant in March UK

Sow Indoors (March)

• Sweet peas — A March indoor sow still produces good results. Pinch tips when 10cm tall.
• Antirrhinums (snapdragons) — Slow growers; start early March indoors.
• Pelargoniums — Need warmth. Propagator recommended.
• Petunias — Surface sow, do not cover. Keep moist and warm.
• Dahlias — Start tubers in pots indoors now for an earlier flowering display.

Direct Sow Outdoors (Late March, Sheltered)

• Cornflowers — Hardy annual. Direct sow from mid-March.
• Poppies — Scatter and rake in. Do not transplant — they hate root disturbance.
• Calendula (pot marigold) — One of the toughest hardy annuals. Direct sow from late March.
• Larkspur — Sow in situ from late March.
• Ammi majus — Hardy annual, direct sow late March.

What NOT to Plant Outdoors in March

These crops need warmth that a British March cannot reliably provide:

• Courgettes, marrows, squash — Wait until late May outdoors. Even indoors, early April is early enough.
• Runner beans and French beans — Frost-tender. Direct sow outdoors from late May only.
• Sweetcorn — Needs warm soil (12°C+). Late May minimum outdoors.
• Basil outdoors — Even a light frost will kill it. Do not plant outside until June.
• Tomatoes outdoors — Sow indoors in March, but plant outside only after the last frost (mid-May to early June depending on region).

March Gardening Tips: Getting More From Early Spring

• Use fleece — A 30g fleece raises soil temperature by 2–3°C and protects against late frosts. Lay it over beds before and after sowing.
• Warm soil before sowing — Lay black plastic or fleece on beds 2–3 weeks before you plan to sow to warm the soil faster.
• Raised beds — Warm up faster than ground level. Ideal for early sowing.
• Succession sow — Sow lettuce, radishes and spinach every 2–3 weeks for continuous harvests through summer, not one large glut.
• Check local frost dates — Southern England averages last frost around mid-April. Scotland and northern England can see frosts into May.

Frequently Asked Questions

What vegetables can I plant in March in the UK?

Indoors: tomatoes, peppers, chillies, aubergines, leeks, celery. Outdoors (late March): broad beans, peas, spinach, lettuce, radishes, beetroot, carrots, parsnips, spring onions.

Is it too early to plant in March in the UK?

Not for indoor sowing or hardy outdoor crops. It is too early for frost-tender vegetables like courgettes and beans outdoors. Check soil temperature — aim for 7°C+ before direct sowing.

Can I plant tomatoes in March in the UK?

Yes — sow indoors in a heated propagator (18–25°C) from mid-March. They will be ready to transplant outdoors after the last frosts, around mid-May.

What flowers should I plant in March UK?

Indoors: sweet peas, antirrhinums, petunias, dahlias, pelargoniums. Outdoors (late March): cornflowers, poppies, calendula, larkspur, ammi majus.

When is the last frost date in the UK?

Southern England: average last frost mid-April. Midlands: late April. North of England and Scotland: late April to mid-May. Always check a local forecast before planting tender crops.