🧅🌱 Sowing Onion Seeds for Spring Onions (UK Guide)

🌱 Introduction: Why Grow Spring Onions from Seed?

Spring onions (also called salad onions or scallions) are one of the fastest, easiest, and most rewarding crops to grow from seed. Unlike bulb onions, they’re harvested young, don’t need much space, and can be grown almost year-round with the right timing.

Sowing onion seeds specifically for spring onions is different from sowing for bulbs. This guide explains when to sow, how thickly to sow, and how to grow tender spring onions quickly and reliably in the UK.

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• Onion Seeds

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• Seed Trays & Module Pots

Essential for avoiding early planting failures caused by cold, wet soil. Seed trays allow you to start vegetables under cover and transplant at the right moment.
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• Seed Compost & Propagator

Using proper seed compost in a propagator gives reliable warmth and drainage, preventing poor germination, damping off, and weak seedlings—a common monthly mistake for beginners.
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📅 When to Sow Onion Seeds for Spring Onions (UK)

Spring onions are very flexible.

✅ Main sowing periods

• February–March → early spring crops
• April–July → main outdoor crops
• August–September → autumn crops
• October–February → under cover only

With protection, you can harvest spring onions almost all year.

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🌡️ Temperature & Light Requirements

Germination

• 10–20°C
• Germination in 7–14 days

Spring onions tolerate cooler conditions better than bulb onions and don’t need intense light once established.

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🌱 Best Compost for Spring Onion Sowing

Use:

• Fine seed compost for sowing
• Light, free-draining compost is ideal

Spring onions grow quickly, so compost quality matters less than for storage onions—but avoid heavy or waterlogged soil.

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🌱 How to Sow Onion Seeds for Spring Onions

1️⃣ Sow Little and Often

For a continuous harvest, sow small batches every 2–3 weeks.

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2️⃣ Sow Slightly Thicker Than Bulb Onions

Spring onions can be grown closer together.

• Sow seeds 5–10 mm apart
• You can even sow in small clusters

Crowding is acceptable because bulbs are not the goal.

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3️⃣ Sow Shallow

• Cover seeds with 5–10 mm of compost
• Do not bury deeply

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4️⃣ Water Gently

• Keep compost evenly moist
• Avoid waterlogging, especially in cool weather

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🌿 Growing On Spring Onion Seedlings

Once seedlings appear:

• Grow in bright light
• Keep compost just moist
• Thin lightly if extremely crowded (optional)

Spring onions are forgiving and recover well from minor stress.

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🪴 Where to Grow Spring Onions

Spring onions are ideal for:

• Open ground
• Raised beds
• Containers and pots
• Window boxes
• Polytunnels and greenhouses

They need very little space and suit small gardens and allotments perfectly.

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🌱 Spacing for Spring Onions

If thinning or transplanting:

• 2–5 cm between plants
• Rows 10–15 cm apart

Closer spacing gives thinner onions; wider spacing gives chunkier stems.

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💧 Watering & Feeding

• Water regularly for tender growth
• Don’t allow soil to dry out fully
• Light feeding helps, but avoid heavy nitrogen

Uneven watering can cause tough or bitter stems.

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⏱️ How Long Until Harvest?

Spring onions are quick.

• Ready in 6–10 weeks from sowing
• Harvest when stems reach pencil thickness
• Pull whole plants or cut above the base for regrowth (some varieties)

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🌾 Best Onion Varieties for Spring Onions

Look for varieties labelled:

• Spring onion
• Salad onion
• Bunching onion

Bulb onion varieties can be used, but spring onion types give better texture and flavour.

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🚫 Common Mistakes When Growing Spring Onions

• Letting compost dry out
• Sowing once instead of succession sowing
• Growing too densely without airflow
• Leaving plants too long (they become tough)

Spring onions are best young and tender.

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🧠 Key Takeaway

Sowing onion seeds for spring onions is quick, easy, and ideal for succession growing. Sow little and often, grow them close together, keep watering steady, and harvest young.

If you want one of the most reliable crops in the UK, spring onions grown from seed are hard to beat.

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