Autumn Onion Sets for an Early Crop

Autumn onion sets give you the earliest onions of the year. Plant overwintering varieties in October and you’ll be lifting bulbs in June, weeks before spring-planted sets are ready. They use beds that would otherwise sit empty over winter and need very little care once they’re in.

This guide covers the best varieties, when and how to plant, winter care and harvesting. For spring-planted maincrop onions, see our main guide to growing onions.

Why autumn onion sets crop so early

Onion sets are small, partly grown onion bulbs. Autumn sets are special overwintering varieties, many of them Japanese types, bred to root in autumn, sit through winter and bulb up early the next summer.

The head start is the whole point. A spring-planted set starts from scratch in March. An autumn set has already rooted before winter, so it shoots away as soon as the days lengthen and the soil warms.

An autumn set roots before winter, like the one on the left, so it’s ready to grow away fast in spring.

Best overwintering onion varieties for UK gardens

Choose sets sold for autumn planting. Ordinary spring sets planted in autumn are much more likely to bolt.

If you’re torn, plant two varieties to spread the harvest. Our comparison of the best UK onion varieties covers spring types too.

Overwintering onions come in brown, red and white-skinned types, so you can have colour on the plate early in summer.

When to plant autumn onion sets in the UK

Plant from late September to late October. The sets need time to root and make a little leaf before winter, but not so much that they grow big and bolt in spring.

October is the sweet spot: sets have time to root before winter without growing big enough to bolt.

• Scotland and northern England: plant from mid to late September.
• Most of England and Wales: October is ideal.
• The mild south and south west: you can carry on into early November.

Planting in early September is a common mistake. Sets that grow large before winter are more likely to run to seed in spring. Our October planting guide lists other crops to sow and plant at the same time.

How to plant autumn onion sets step by step

Planting is quick once the bed is right. Most of the effort goes into drainage.

1. Pick the sunniest, best-drained bed. Onions rot in cold, wet ground, so a raised bed is worth it on heavy clay.
2. Improve drainage. Fork in grit if your soil is heavy. Don’t add fresh manure now, as it encourages soft growth. A bed manured for a previous crop is ideal.
3. Firm the soil. Tread the bed lightly and rake it level. Loose soil lets frost lift the sets out.
4. Push the sets in 10cm apart, in rows 25-30cm apart, so the tip just shows above the surface. Firm the soil around each one.
5. Water lightly only if the soil is dry. Autumn soil is usually moist enough.

Push each set in until only the papery tip shows. Too deep and it can rot; too shallow and birds tug it out.

How to protect overwintering onions

Once planted, autumn onions face three threats: birds, frost heave and rot. Each has a simple answer.

Birds such as blackbirds and pigeons pull new sets out by their dry tips, often within days. Cover the bed with netting or fleece for the first few weeks until the roots take hold. Push any pulled sets straight back in.

Frost heave happens when frozen soil swells and lifts the shallow sets. Walk the bed after hard frosts and gently re-firm any that have lifted.

Rot is the big winter killer on wet ground. Good drainage is the only real cure. Fleece helps in a hard freeze, but warmth matters much less than drainage.

Fleece keeps birds off new sets and takes the edge off a hard freeze, but drainage still matters more.

Caring for autumn onions in spring

Growth picks up from February. Now’s the time to help them along.

• Feed with a nitrogen-rich fertiliser, such as sulphate of ammonia, in late winter or early spring, following the pack rate.
• Weed carefully by hand. Onions hate competition, and a hoe can nick the bulbs.
• Water in dry spells in spring, then ease off as the bulbs swell.
• Pull any plant that starts to flower. Use it straight away, as it won’t store.
• Check for disease weekly from March. Downy mildew shows as pale, fuzzy grey-purple patches that make leaves yellow and collapse. Space plants well and remove affected ones early. Our guide to onion downy mildew explains more.

Overwintered onions grow fast once the days lengthen, putting them weeks ahead of spring plantings.

Month-by-month calendar for autumn onions

How to harvest autumn onions

Autumn onions tell you when they’re ready. The leaves flop over and turn yellow, usually in June or July. Let them fall naturally rather than bending them over.

Lift the bulbs on a dry day, easing them up with a fork. Lay them out somewhere sunny and airy, or under cover if it’s wet, for a week or two until the skins feel papery.

These onions don’t store well. They soften or sprout within a few weeks, so treat them as a fresh summer crop. Use them up by late summer while your spring-planted maincrop onions keep in the shed. Our guide to drying and curing onions covers storing the maincrop.

Dry lifted onions until the skins are papery, then enjoy them fresh through the summer.

What to plant alongside autumn onions

Autumn onions share the winter beds well with two other crops that follow the same rhythm.

Garlic goes in at the same time and likes the same firm, free-draining ground. Keep it in the same rotation bed as your onions, so the whole onion family moves together each year. See how to grow garlic for timings.

Broad beans sown in October or November stand through winter and crop in late spring and early summer. Together, these crops help fill the hungry gap in late spring, when winter stores run out and spring sowings aren’t ready yet.

Common mistakes with autumn onion sets

Using spring sets. Ordinary sets planted in autumn often bolt or rot. Buy varieties sold for autumn planting.

Planting too early. Sets planted in early September can grow too big before winter and bolt in spring. Wait until late September or October.

Wet, heavy ground. Cold, waterlogged soil rots sets over winter. Raise the bed or add grit on clay.

Burying the sets. Fully buried sets sit wet and rot. Leave the tip showing and net against birds.

Expecting them to store. These are for eating fresh. Grow maincrop onions to store for winter.

Frequently asked questions

When should I plant autumn onion sets in the UK?

Plant from late September to late October, or into early November in the mild south. The sets need time to root before winter, but shouldn’t grow too big before the cold arrives.

Can I use any onion sets for autumn planting?

No, use sets sold as overwintering or autumn-planting varieties. ‘Senshyu’, ‘Radar’, ‘Electric’ and ‘Autumn Champion’ are bred to sit through winter. Ordinary spring sets planted in autumn are much more likely to bolt or rot.

How early do autumn onions crop compared to spring-planted onions?

Autumn onions are usually ready in June and July, several weeks earlier. That makes them handy in early summer, when last year’s stored onions have usually run out.

Do overwintering onions store well?

No, overwintering onions keep only a few weeks, so eat them fresh. They soften or sprout much sooner than maincrop onions. Grow maincrop onions as well if you want bulbs that keep into winter.

Why do my autumn onions keep bolting?

Usually because they were planted too early or the variety wasn’t an overwintering type. Sets that grow large before winter are more likely to flower in spring. Plant in October and choose varieties sold for autumn planting.

What soil do autumn onion sets need?

They need full sun and free-draining soil that never sits wet. Cold, waterlogged ground rots the sets over winter, so use a raised bed or add grit on heavy clay.

Should I protect autumn onion sets over winter?

Net them against birds and re-firm any sets lifted by frost. Birds pull new sets out by their dry tips. Fleece helps in a hard freeze, but good drainage matters far more than warmth.

If your onions do run to seed, our guide to stopping onions bolting explains what to do next. Find more veg guides in our growing section.