When to harvest your onions & how to store them

There’s a particular kind of smugness reserved for the gardener who reaches into a net bag in the dead of January, pulls out a firm, papery homegrown onion and lobs it into a stew. No supermarket plastic. No sad, sprouting specimen from the back of the cupboard. Just months-old, home-cured deliciousness that you grew.

But here’s the bit nobody tells you when you’re happily sowing seeds in early spring: getting a fat, glossy onion out of the ground is only half the job. When you harvest onions and how you store onions is the difference between a pantry full of bulbs that see you through winter and a soggy, mouldy heap by October half term.

This is your complete guide to when to harvest onions in the UK, how to nail the curing process, and how to store onions so they keep and keep and keep.

New to the whole business of growing onions? Start with our full how to sow and grow onions guide, then come back here for the grand finale.

When to harvest onions in the UK

The short, slightly unsatisfying answer is: it depends on when you planted and what you planted. The good news is your onions will tell you loudly and clearly when they’re ready. You just need to know the signals.

For most maincrop onions sown indoors or direct sown in early spring, harvest time falls between mid summer and early autumn, roughly July to October here in the UK. Our ever-reliable Onion Galacticus, for instance, produces its huge yellow bulbs ready for lifting any time from July right through to October.

If you grew overwintering onions like the brilliant Senshyu or Karmen sown the previous August or September, you’ll be gleefully harvesting your onions much earlier, often in June and July, for that lovely early crop while everyone else is still waiting.

How to tell when onions are ready to harvest

Forget the calendar for a moment and go and look at your onion tops. The plant does the announcing. Your onions are ready to harvest when:

• The leaves begin to turn yellow and flop over. Onions are ready when “the foliage flops over and starts to yellow.” This is the plant telling you it’s finished putting energy into the bulb and is ready to be lifted.
• The bulbs have reached a good mature size. Gently scrape away a little soil and have a peek. If the onion bulbs look plump and the papery outer layer has started to form, you’re in business.
• The necks have softened. The join between the onion tops and the bulb goes soft and thin as the plant powers down.

Resist the urge to fold the tops over by hand to speed things along, let them bend and yellow in their own time. A little patience now means better keeping onions later.

One lovely exception: if you’re growing something like Onion Long Red of Florence, you can also harvest the immature bulbs early as a sweet, mild salad onion. Those immature onions won’t store, but they’re a glorious treat straight from the garden while your maincrop finishes bulking up.

Choose a dry spell

Try to harvest your onions during a dry, sunny spot in the weather. Lifting bulbs out of cold, wet, waterlogged ground is asking for rot down the line. If a run of rain is forecast and your onions are ready, get them up, you can always finish drying them undercover.

How to harvest onions without ruining them

When the tops have yellowed and flopped, it’s harvest time. Here’s the careful bit.

Using a fork, gently loosen the soil around each plant and carefully dig the bulbs up rather than yanking them out by the tops, a snapped neck is a fast track to a rotten onion. Lift the whole plant, roots, tops and all, and shake off the excess soil.

Whatever you do, do not scrub, wash or bruise them. Every knock is a bruise, and every bruise is a place for rot to sneak in. Handle your onions like the precious little jewels they are, and lay them out somewhere to begin the all-important curing process.

Curing onions: the step everyone skips (but shouldn’t)

If you take one thing from this whole guide, make it this. Curing onions is the secret to onions that store for months instead of weeks. Skip it and you’ll be composting mushy bulbs before Christmas.

Curing simply means drying the onions slowly so the outer layer of skin turns papery and seals the bulb, and the neck dries right down. It’s the same trick that keeps garlic and shallots sweet all winter, and it makes all the difference.

Here’s how to cure your onions properly:

1. Lay them out in a single layer somewhere warm, dry and with good airflow. A wire rack, a slatted bench, an old pallet or even a spare bit of chicken wire is perfect, because air can circulate underneath. In a good British summer you can cure onions outdoors in the sun; if the weather turns (and it will), move them to a greenhouse, porch, shed or airy windowsill.
2. Keep them out of harsh, direct sunlight if it’s baking hot, you want to dry the skins, not scorch the bulbs. A warm, bright, airy spot is the sweet spot.
3. Leave them to cure for two to three weeks. Our variety guides recommend hanging or laying onions somewhere dry to cure the skin for around two weeks before storage. You’ll know curing is complete when the skins are papery and rustly, the necks are completely dry and tight, and the roots have shrivelled.

Curing done well is genuinely the whole ballgame for long term storage. Rush it and no amount of clever storing will save you.

How to store onions so they keep for months

Congratulations, your onions are cured, dry and ready to be squirrelled away. Now let’s store onions the right way so you’re still eating them next spring.

1. Trim and tidy

Once fully cured, trim the dried roots off and cut the papery tops back to about 2–3cm above the bulb. Or, if you’re feeling fancy, leave the tops long and plait them into an old-fashioned onion string to hang in the kitchen, beautiful and practical.

2. Pick only the perfect ones for storage

Sort ruthlessly. Any onions that are soft, thick-necked, bruised or damaged will not store, pop those in the kitchen to use as your fresh onions over the next few weeks. Only firm, well-cured, blemish-free bulbs go into long term storage.

3. Store cool, dark and airy

Onions store best somewhere cool, dark and dry with plenty of ventilation, think a frost-free shed, garage, pantry or spare room. The magic conditions are roughly 0–10°C, low humidity and good air circulation. Avoid anywhere warm and damp (rot and mould) or anywhere they’ll freeze.

Keep them out of the light, too. Light and warmth are the two things that nudge stored onions into sprouting, so a cool, dark spot keeps them dormant and happy for far longer.

4. Use the right containers

Give your onions air. Store them in net bags, mesh sacks, open slatted crates, wire racks or hung as strings, anything that lets air move freely around each bulb. Never seal onions in plastic bags or airtight tubs, where trapped moisture will have them rotting in no time. And keep them away from your stored potatoes, which give off moisture and gases that make onions spoil faster.

5. Check on your stash

Every few weeks, have a quick rummage and remove any onions that have started to soften or sprout. One bad onion really can spoil the bunch, so a little vigilance keeps the rest of your hoard in perfect nick.

How long will homegrown onions keep?

With good curing and the right storage, firm maincrop storage onions such as Galacticus will happily keep for several months, often right through winter and into early spring. Sweeter, milder varieties and those gorgeous salad-type reds have a shorter shelf life and are best enjoyed fresh within a few weeks, so eat those first and save the tough keepers for the long haul.

A rough rule of thumb: the stronger the flavour and the tighter the skin, the longer an onion will store.

Want to preserve onions beyond storing?

If you’ve had a bumper year (well done you), storing whole bulbs isn’t your only option. You can preserve onions in all sorts of delicious ways to make the glut last even longer:

• Freeze them – peel, chop and open-freeze, then bag up ready to tip straight into the pan.
• Pickle them – small onions and shallots are made for a jar of malt vinegar and spices.
• Dehydrate them – dried onion flakes and powder are brilliant, and a wonderful way to use up smaller bulbs.
• Caramelise and freeze – batch-cook a mountain of jammy caramelised onions and freeze in portions. Future you will weep with joy.

Ready to grow your own?

There is honestly nothing quite like a homegrown onion, the flavour, the satisfaction, the winter smugness. And it all starts with a packet of seeds.

Happy growing, happy harvesting, and here’s to a pantry full of onions come winter.