How to Grow Spring Onions in the UK

How to Grow Spring Onions in the UK: Complete Growing Guide

Spring onions (salad onions or scallions) are quick-growing, versatile vegetables perfect for UK gardens. With their mild flavour and crisp texture, they're ideal for salads, stir-fries, and garnishes. Easy to grow and ready to harvest in just 8-12 weeks, spring onions can be sown almost year-round for continuous harvests. This comprehensive guide will show you how to grow spring onions successfully.

When to Sow Spring Onions

Spring onions can be sown almost continuously for year-round harvests:

• Outdoor sowing: March to September for spring, summer, and autumn harvest
• Under cover: September to February in greenhouses, polytunnels, or cold frames for winter and early spring harvest
• Succession sowing: Sow small batches every 2-3 weeks for continuous supply
• Hardy varieties: Use winter-hardy varieties for autumn sowings

Soil Preparation

Spring onions are adaptable but prefer well-drained, fertile soil:

• Soil type: Any well-drained soil; they tolerate most conditions
• Add organic matter: Dig in well-rotted compost or manure several weeks before sowing
• Avoid fresh manure: Don't add fresh manure immediately before sowing
• pH level: Slightly acidic to neutral (pH 6.0-7.0)
• Rake fine: Create a fine, level seedbed free from large clods

How to Sow Spring Onions

Spring onions are best sown directly where they'll grow:

1. Create drills: Make shallow drills 1cm (½ inch) deep, 10-15cm (4-6 inches) apart
2. Sow thinly: Sprinkle seeds thinly along the drill, aiming for 1cm spacing
3. Cover lightly: Cover with fine soil and firm gently
4. Water well: Water gently but thoroughly
5. Germination: Seeds germinate in 7-14 days

Alternative: Multi-sowing in modules

• Sow 5-6 seeds per module for early crops
• Don't thin - plant out the entire clump
• Space clumps 10cm (4 inches) apart
• Harvest individual onions from each clump as needed

Thinning Seedlings

Thinning isn't always necessary for spring onions:

• Spring onions can be grown quite close together
• Thin to 2-3cm (1 inch) apart if very crowded
• Use thinnings in salads - they're perfectly edible
• For larger bulbs, thin to 5cm (2 inches) apart

Ongoing Care

Spring onions are very low-maintenance:

• Watering: Water regularly during dry spells to keep soil evenly moist
• Weeding: Keep weed-free, especially when young; hand-weed carefully to avoid damaging shallow roots
• Feeding: Generally no feeding needed; avoid high-nitrogen fertilisers
• Protection: Cover autumn sowings with cloches or fleece for winter protection

Common Problems

Onion fly: Larvae tunnel into bulbs causing yellowing and wilting. Cover with fine mesh or fleece immediately after sowing.

Downy mildew: Grey-purple fuzzy growth on leaves. Ensure good spacing and air circulation; remove affected plants.

Bolting: Plants run to seed prematurely. Use bolt-resistant varieties and ensure consistent watering.

White rot: Fungal disease causing yellowing and rotting. No cure; practice crop rotation and don't grow onions in affected soil for 8 years.

Harvesting Spring Onions

Spring onions are ready to harvest quickly:

• Timing: Ready 8-12 weeks after sowing, depending on variety and season
• Size: Harvest when stems are pencil-thick (about 1cm diameter)
• Pull gently: Grasp close to the base and pull straight up, or use a hand fork to loosen soil first
• Harvest as needed: Pull individual onions as required, leaving others to grow
• Don't leave too long: Harvest before bulbs start to swell significantly
• Morning harvest: Pick in the morning when they're crispest

Storage

Spring onions are best eaten fresh but can be stored briefly:

• Fresh is best: Use within 2-3 days of harvesting for best flavour
• Refrigerator: Stand roots in a jar of water in the fridge for up to 1 week
• Plastic bags: Store unwashed in plastic bags in the fridge for up to 1 week
• Freezing: Chop and freeze in bags or ice cube trays for up to 6 months
• Regrow: Place roots in water on a windowsill to regrow green tops

Recommended Varieties

Summer Varieties:

• White Lisbon: Classic variety, quick-growing, mild flavour
• Guardsman: Uniform, upright growth, good disease resistance
• Ishikura: Japanese variety, long white stems, no bulbing
• Red Beard: Attractive red-purple stems, mild flavour

Winter-Hardy Varieties:

• White Lisbon Winter Hardy: Hardy selection for autumn sowing
• Performer: Very hardy, overwinters well, early spring harvest
• Winter White Bunching: Extremely hardy, sow August-September