When to harvest onions – here's how to tell if they're ready, and how to store them so they last

Autumn is a great time to be a gardener, especially if you've been growing your own vegetables. If you're wondering when to harvest onions, you could be enjoying your hard-earned bulbs sooner than you think.

Learning how to grow onions is incredibly rewarding – the bulbs offer even more flavour than the ones you'll find at the supermarket, and it's always fun to tell dinner guests that you've grown the ingredients yourself.

The general window for harvesting onions is late summer to early autumn, but knowing exactly when to harvest onions will largely depend on the type you're growing and when you planted them.

So, we've checked in with garden experts to help you determine when onions are ready to be harvested, whether you've grown the bulbs from sets or you're waiting on a crop of spring onions.

What you'll need

Harvesting onions for immediate use

If you're hoping to bring your onions into the kitchen right away, harvesting rules are pretty flexible. Generally, you can lift the bulbs as soon as they're the size you need.

'Simply loosen the soil around the onion with a fork and ease it gently from the soil,' advises gardening expert Lucie Bradley. Then, clean them and bring them straight into the kitchen.

Lucie Bradley

Encouraged to garden since she was old enough to walk, Lucie has been working in the gardening industry for over 28 years. She has been lucky enough to talk to both amateur and professional gardeners every day of the week and is always learning. She believes you can never know everything about gardening as it constantly evolves.

This also applies to spring onions, which are a great choice for beginners as one of the easiest vegetables to grow.

'From sowing to harvesting, it can take around eight weeks for spring onions to be ready,' says Lucie. 'Depending on the variety, growing conditions and how large you want the onions to grow, this could be up to ten weeks – but always check the seed packet for the supplier's recommendations.

'Spring onions are ready to harvest when they are about 15cm in height and between 1.5 to 2.5cm wide.'

Generally, the longer you leave spring onions to grow, the stronger they'll taste. For the best flavour, Lucie recommends harvesting as close to the directions on the seed packet as possible.

When to harvest onions for storage

For large, fully-grown bulbs that you'll want to store, wait until the plants have finished growing before harvesting. If you're wondering when that is, there are a couple of tell-tale signs that your onions have reached full maturity.

'A general guide would be to wait until the onion 'stem' begins to die back, leaving just the onion bulb itself, and this is often in late summer,' says Andy Tudbury, head gardener at Belvoir Castle. 'When you go to pick the onion, you should feel very little resistance from the roots. The outer skin of the onion may also be dry and splitting away.'

Once the leaves begin to flop over, Lucie recommends waiting for a week before harvesting.

There's actually science behind why you should wait until the foliage dies off. 'As the foliage shrivels up, it effectively seals off the top of the onion,' Lucie says.

That way, your onions are set for storage. Which brings us to how to store your onions...

How to store onions

Now you've got them out of the ground, it's time to properly store your onions so that none of your bulbs go to waste. But first, you'll need to remove any damaged bulbs.

'Get rid of any shrivelled growths or roots,' says Lucie. 'What’s important not to remove are the loose skins around the bulb of the onion, as these help to protect it while it's stored.'

As with most vegetables, the best conditions for storing onions are cool, dark and dry, with plenty of ventilation. Many growers choose to hang their onions in nets or pop them on top of newspaper while they dry, and this process can take a few weeks.

Once the skins have turned papery, you can store them away in wooden crates, or even plait them. 'If you are going to braid the onions, leave about 8cm of stem in place,' says Lucie.

FAQs

Do you harvest onions before or after they flower?

You should always harvest your onions before the plants start to flower.

'Once an onion forms a flower spike, and subsequently goes to seed, it will damage the core of the actual bulb and eventually lead to the onion rotting from the centre outwards,' explains Andy from Belvoir Castle.

Do you harvest onions when they fall over?

If the leaves on your onion plants are beginning to flop over, it's a good sign that they've finished growing and there's a mature bulb waiting beneath the soil. As Lucie suggests, it's a good idea to wait for about a week after you notice this change in the foliage to give your onions a chance to seal themselves, ready for storage.

So, now we know when to harvest onions. But if you missed the planting window this year, it's never too late to learn when to plant onion sets and grow your own bulbs.