What Seeds to Plant in March | Garden & Allotment Sowing Guide

Introduction: Start Your Growing Season Strong in March

As winter fades and daylight hours stretch longer, March marks the true beginning of the gardening year in the UK. Whether you’re tending a backyard garden, balcony containers, or an allotment plot, this is the month to get sowing. With warming soil and the first hints of spring in the air, you can kickstart your growing season by planting a wide range of vegetables, herbs, and flowers.

This complete March sowing guide will help you plan what to grow, whether you’re sowing indoors, under cover, or directly outdoors. Packed with practical advice and high-impact seed suggestions, this guide is perfect for new and experienced growers alike.

1. Understanding the March Growing Window in the UK

Is It Warm Enough to Start Planting?

March can be unpredictable, with frosty mornings one week and mild sunshine the next. But don’t let that stop you — with the help of cloches, greenhouses, and windowsills, you can get a head start on the season.

Tips for March Planting Success:

Use a heated propagator or sunny windowsill for heat-loving crops.
Cover soil with plastic sheeting to warm it up before direct sowing.
Check for frost dates in your region before planting outside.

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2. Vegetables to Sow in March

Your Spring Kitchen Garden Starts Here

March is ideal for starting off cool-season vegetables. Some can go directly outdoors, while others should be started indoors or under cover.

Sow Outdoors:

Carrots – Early varieties like ‘Nantes’ or ‘Early Scarlet’.
Parsnips – Long season crop; sow early for best results.
Broad beans – Hardy and perfect for early crops.
Beetroot – Begin with ‘Boltardy’ for stability in cooler soils.
Spinach – A fast grower and cold-hardy.
Lettuce – Choose cold-tolerant varieties like ‘Little Gem’ or ‘Lollo Rosso’.

Sow Indoors / Under Cover:

Tomatoes – Start now in a heated propagator or warm windowsill.
Peppers & Chillies – Need heat and light to germinate successfully.
Aubergines – Another heat lover; start now for an early summer crop.
Celery – Requires a long season, so an early start is key.
Brussels sprouts – Sow now for winter harvesting.

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3. Herbs to Sow in March

Flavour Your Food Straight from the Garden

March is the ideal time to get started with culinary herbs, many of which are simple to grow from seed.

Sow Indoors:

Basil – Needs warmth; sow in a propagator or on a warm windowsill.
Parsley – Slow to germinate but very hardy once established.
Coriander – For leaf production, sow in cooler temperatures.
Chives – Easy to grow and comes back year after year.
Oregano – Sow indoors now and transplant in late spring.

Sow Outdoors (with cover or in milder areas):

Dill
Rocket
Thyme

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4. Flowers to Sow in March

Brighten Your Garden and Attract Pollinators

If you’re dreaming of vibrant blooms through summer and autumn, now is the time to start sowing your favourites.

Hardy Annuals – Sow Outdoors:

Calendula – Bright orange/yellow flowers; edible too!
Cornflowers – Pollinator-friendly and easy to grow.
Nigella (Love-in-a-Mist) – Great for cottage garden style.
Larkspur – Needs a cold start, so March is ideal.
Poppies – Direct sow into prepared beds.

Tender Annuals – Sow Indoors:

Cosmos – Needs warmth to germinate but flowers all summer.
Zinnias – Sow now for transplanting in late spring.
Antirrhinums (Snapdragons) – Benefit from early sowing.
Petunias – Popular for baskets and containers.
Marigolds – Easy to grow and great for companion planting.

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5. March Sowing by Gardening Method

Match Your Method to Your Space

Greenhouse Sowing:

Perfect for tomatoes, cucumbers, chillies, early lettuce, and spinach.

Indoor Windowsill Sowing:

Ideal for heat-loving herbs and vegetables like basil, aubergines, and peppers.

Direct Sowing Outdoors:

Best for root vegetables and hardy annual flowers — make sure soil is weed-free and warmed.

Under Cloche or Cold Frame:

Protects early carrots, salad leaves, and radishes from frost and wind.

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6. Top Tips for Germination in Early Spring

Boost Success Rates with These Proven Tactics

Use fresh seed compost — fine-textured and sterile.
Don’t overwater — keep compost moist, not soggy.
Label everything clearly — it’s easy to forget what you planted!
Ventilate propagators daily — to prevent mould and damping off.
Use bottom heat for slow starters like aubergines or chillies.

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7. Succession Sowing: Keep the Crops Coming

Staggered Planting = Continuous Harvests

Rather than planting everything at once, sow little and often.

Great Crops for Succession Sowing:

Salad leaves
Radishes
Beetroot
Spinach
Spring onions

Sow a new row every 2–3 weeks through March and April for regular harvests.

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8. Seeds to Avoid Planting in March (Unless Indoors)

Hold Off On These Until April or May Unless You Have Protection

French beans & runner beans – Wait until April unless in a heated propagator.
Courgettes & squashes – Can be sown in late March but need warmth.
Sweetcorn – Notoriously frost-sensitive, wait until April indoors.
Cucumbers – Best started in a propagator or warm greenhouse in late March.

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9. Create Your Personalised March Sowing Schedule

Stay Organised and Beat the Weather

Make a list or printable calendar to track:

What you’ve sown
When you sowed it
Where it’s growing (indoors/outdoors/under cover)
Expected transplanting dates

Use tags, a garden journal, or a digital app like VegPlotter or Plan-A-Garden.

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Conclusion: March is the Month to Get Growing

March is your golden opportunity to jump-start your growing season, no matter what kind of space you have. With seeds sown now, you’ll set yourself up for a productive spring and summer full of colour, flavour, and fresh harvests.

From early carrots and salad leaves to vibrant cosmos and tomatoes for later in the year, the choices are endless — and the excitement of sowing new life is what gardening is all about. So grab your seed trays, warm up your compost, and get planting!

Top 10 FAQs: What to Sow in March in the UK

1. Can I start sowing seeds outside in March?

Yes, but stick to hardy vegetables and flowers, and warm the soil if possible.

2. Is March too early to sow tomatoes?

No — March is the ideal time to start tomatoes indoors in the UK.

3. What herbs can I grow from seed in March?

Parsley, coriander, basil, and chives are great choices — start indoors for best results.

4. Should I use a propagator in March?

Yes, especially for chillies, tomatoes, aubergines, and other heat-lovers.

5. Can I plant root vegetables now?

Yes — carrots, parsnips, beetroot, and radishes can be sown directly.

6. What flowers can I sow in March?

Start hardy annuals outdoors and tender ones like cosmos indoors.

7. How do I know when to move seedlings outside?

Harden them off once the risk of frost has passed — usually in April/May.

8. Is March good for succession sowing?

Definitely — start with salads, radishes, and beets every few weeks.

9. Can I grow potatoes in March?

Yes! It’s a great time to plant chitted seed potatoes into prepared beds or containers.

10. What vegetables shouldn’t I sow yet?

Wait on courgettes, beans, and sweetcorn unless you have a heated propagator or greenhouse.