spring onions on a chopping board

How to Grow Spring Onions

Geoffrey Allerton

There’s nothing quite like snipping a handful of fresh spring onions straight from the garden to liven up a salad or stir-fry. They’re one of the quickest, easiest crops for UK gardeners — ready in just a few weeks, happy in beds, pots, or even a glass of water on the windowsill. Whether you call them spring onions, green onions, or scallions, they’re the same versatile crop. Welsh onions look similar too, but unlike the others, they’re perennial and will return year after year.

Choosing Varieties

The classic UK favourite is ‘White Lisbon’ — crisp, mild, and quick to grow. ‘Ishikura’ is a Japanese bunching onion that grows tall stems without forming a bulb, ideal for cut-and-come-again harvesting. ‘Performer’ offers a mild flavour with good disease resistance. If you’d like something longer-term, try Welsh onions, which regrow year after year once established.

When to Sow Spring Onions in the UK

  • March–September: Main outdoor sowing season.
  • Undercover sowing: Start earlier (Feb) in a greenhouse or cold frame.
  • Successional sowing: Sow every 2–3 weeks for a steady supply through summer.

Soil, Sunlight, and Pots

Spring onions like:

  • Light, sandy, well-drained soil – they grow quickest in lighter soils. Heavy clay should be improved with compost.
  • Full sun – though partial shade is tolerated.
  • Pots/containers – at least 15–20cm deep. A trough or window box works perfectly. They don’t need heavy feeding, but adding a little compost to the bed before sowing helps.

How to Grow Spring Onions

Direct Sowing Outdoors

  1. Make shallow drills about 1.5cm deep.
  2. Sow thinly, spacing rows 15cm apart.
  3. Cover lightly with soil, water gently, and keep weed-free.

Sowing in Modules for Transplanting

  • Sow a few seeds per cell in a module tray.
  • Harden off and plant out clumps when 10cm tall.
  • Each cluster grows into a neat bunch for pulling together.

Growing Indoors

  • Sow in pots or troughs on a sunny windowsill.
  • Year-round cropping is possible with good light. In winter, a grow light helps prevent spindly seedlings.

Growing from Scraps / Store-Bought Onions

  • Place the root ends of supermarket spring onions in a glass of water. They’ll regrow leaves in a few days.
  • For stronger regrowth, plant the rooted bases in compost. Note: this is a fun way to stretch your onions, but it won’t give the same yield as sowing seed.

Care and Maintenance

  • Watering: Keep soil moist but not waterlogged. In pots, water little and often.
  • Weeding: Seedlings are fine and easily crowded out, so weed regularly.
  • Feeding: Usually unnecessary, but a light liquid seaweed feed helps in containers.
  • Pests: Slugs may nibble seedlings, and onion fly can occasionally strike, though it’s less common than with bulb onions.

How Long Do Spring Onions Take to Grow?

Most spring onions are ready 6–8 weeks after sowing. In warm summer weather, they may be ready sooner.

Harvesting and Regrowing

  • Harvesting: Pull whole plants when pencil-thick, or cut leaves for a milder regrowth.
  • Cut-and-come-again: Varieties like ‘Ishikura’ can be cropped this way.
  • Regrowing from roots: Shop-bought onions can be replanted for a second flush of leaves.
  • Collecting seeds: If left to flower, they’ll produce seed heads. Let them dry fully on the plant, then collect and store seeds in a cool, dry place for next year.

Common Questions Answered

  • Can I grow spring onions from a spring onion? Yes — replant the root base from shop-bought ones.
  • What is the best way to grow them? Successional outdoor sowing is easiest for a steady supply.
  • What month do you plant spring onions? March–September outdoors, earlier under cover.
  • How deep do pots need to be? 15–20cm is plenty.
  • Do spring onions come back every year? Not usually, unless you’re growing Welsh onions.
  • Do slugs eat spring onions? Occasionally young seedlings, but rarely once grown.
  • Do spring onions multiply? Some bunching types do, producing clumps you can harvest together.
  • Can I grow spring onions indoors? Yes — on windowsills or under lights, year-round.
  • How often should you water spring onions in pots? Little and often, keeping the compost just damp.

Conclusion

Spring onions are a brilliant, space-saving crop — quick to sow, quick to grow, and quick to harvest. Sow little and often from spring through summer, and you’ll never be without a fresh bunch to liven up your cooking. Within weeks, you’ll have homegrown flavour at your fingertips — far fresher and tastier than anything from the supermarket.