Best Onion Varieties to Grow From Sets or Seed

The best onion for most UK gardens is Sturon, grown from sets. It’s reliable, slow to bolt and keeps well into winter. Add Red Baron for colour, and try a seed-grown variety like Ailsa Craig if you want big, mild onions.

This guide helps you choose varieties and decide between sets and seed. Planting, weeding and harvesting are covered in the onion growing guide linked at the end.

Sets or seed: which is right for you?

Onion sets are small, part-grown bulbs. They’re the easy choice: you push them into the soil in spring and they grow away quickly. Seed is cheaper per onion and offers far more varieties, but it needs sowing early under cover.

Heat-treated sets have been warmed at the nursery to stop them running to flower. Buy these for spring planting if you can, especially for red onions, which are more prone to bolting.

Onion sets pushed into the soil along a string line, with just the tips showing. Sets are the easiest way to start.

Many growers do both. Plant sets for the main crop that goes into store, and sow a few seeds for big onions or a favourite variety you can’t buy as sets.

Onion varieties compared

Growing a few varieties side by side is a good way to find your favourites. Mix a reliable keeper with a red and something mild.

Best onions for storing through winter

Sturon is the classic choice. It’s a round, golden-brown onion that grows well from sets, rarely bolts and keeps well into the new year. Centurion is similar, a little earlier and also slow to bolt. Setton is an improved Sturon type with the same good keeping.

Hercules makes big, firm, slightly elongated bulbs that store well. Stuttgarter Giant is an old favourite with flattish bulbs that are easy to slice. From seed, Bedfordshire Champion is a traditional, mild-flavoured brown onion that keeps well.

Storing well depends as much on drying as on variety. Lift onions when the tops have flopped and yellowed, and dry them in the sun or a dry, airy shed until the necks are papery. Store in nets or trays somewhere cool, dry and frost-free. The guide to storing onions, garlic and shallots has the details.

Well-dried onions stored in shallow crates in a cool shed. Use the reds first, as they usually don’t keep as long as browns.

Best red onions to grow

Red Baron is the most popular red onion. It has deep red skin, pink-ringed flesh and a good strong flavour, and it’s available as sets or seed. Karmen is another red from sets that keeps fairly well.

Lift red onions once the tops have flopped and yellowed, and dry them well. Reds usually keep less well than browns, so use them first.

Red onions are more likely to bolt than brown ones, so heat-treated sets are worth the extra cost. They also tend not to keep as long, so use them before your brown onions. For a mild red to eat raw, the long, torpedo-shaped Long Red Florence is grown from seed and is lovely in summer salads.

Best onions from seed for size and flavour

Ailsa Craig is the best-known seed onion. It makes big, round, straw-coloured bulbs with a mild flavour. It’s lovely fresh but doesn’t keep long, so eat it in late summer and autumn.

Kelsae is the classic giant for the show bench. It needs sowing in a heated greenhouse in midwinter and plenty of care. The guide to growing exhibition onions covers it in full.

Sow seed under cover in January or February, in modules or trays, at about 10-15°C. Plant the young onions out in April once they’ve been hardened off. A few seeds per module can be planted out as a clump, which gives you smaller onions with less work.

Seed-grown onions start life like fine blades of grass. Sow them under cover in January or February and plant out in April.

Best onions for autumn planting

Senshyu and Radar are reliable brown or yellow onions for planting in autumn. Electric is the red one. Plant the sets in September or October, and they’ll be ready to lift in June or July, filling the gap before spring-planted onions.

These overwintering onions don’t store for long, so eat them through summer. Choose a well-drained spot, as they sit in the ground all winter. Only use varieties sold for autumn planting. Ordinary spring sets planted in autumn are likely to bolt. The guide to autumn onion sets explains planting and winter care.

Common mistakes when choosing onion varieties

• Expecting giant onions to keep. Ailsa Craig and Kelsae are for eating fresh or showing. Grow Sturon or Centurion for the store.
• Planting spring sets in autumn. Use proper overwintering varieties like Senshyu or Radar for autumn planting.
• Buying soft or sprouting sets. Choose small, firm sets, about the size of a marble. Big sets are more likely to bolt.
• Relying on red onions for winter. Reds usually keep less well. Grow a brown onion as your main storage crop.
• Forgetting about shallots. If you want something that keeps really well and multiplies, add a row of shallots.

If a flower spike does appear, snap it off and use that onion first. The guide to stopping onions bolting explains the causes. Now you’ve picked your varieties, read the full guide to growing onions for planting and harvesting, or browse more crops on the growing veg hub.

Frequently asked questions

What is the best onion variety to grow in the UK?

Sturon is a reliable all-round onion for UK gardens. It grows well from sets, resists bolting and stores well. Red Baron is the popular red choice. Ailsa Craig, grown from seed, makes large, mild bulbs but doesn’t keep as long.

Should I grow onions from sets or seed?

Sets are easier and quicker, while seed is cheaper and offers more varieties. Sets have a head start and cope better with a cold, wet spring. Seed needs sowing early under cover but gives you giant and specialist varieties.

Which red onion stores longest?

Red Baron and Karmen are among the better-keeping red onions. Most reds still store less well than brown onions, so use them first. Dry them well in the sun before storing somewhere cool, dry and airy.

What is the largest onion variety?

Kelsae and Ailsa Craig grown from seed make the biggest onions. Kelsae is the classic show giant. Ailsa Craig is easier and makes large, mild kitchen onions. Big onions don’t store as well as smaller keepers like Sturon.

Which onion varieties are best for autumn planting?

Senshyu, Radar and Electric are reliable autumn-planting onions. Plant the sets in September or October for a crop in June or July. They don’t store for long, so eat them before your spring-planted onions.

How do I stop onions from bolting?

Buy heat-treated sets and choose bolt-resistant varieties like Sturon or Centurion. Don’t plant into cold, wet soil too early in spring. If a flower stem appears, snap it off and use that onion first.