By late July and through August, the onion bed starts sending you a signal: the tall green tops begin to soften, lean over, and flop to the ground. That is the moment most gardeners either get right or get wrong. Pull too early and the bulbs stay small and watery; leave them too long and they start to rot in the ground or push out fresh roots that ruin their keeping quality. Getting the timing right, and then curing and storing the crop properly, is the difference between onions that last a few weeks and onions that see you through to next spring. This guide walks you through the whole process step by step.

What You'll Need

Harvesting onions well takes very little kit, but a few things make the job cleaner and the results better:

A garden fork – for gently lifting bulbs without slicing into them
A dry, sunny spell in the forecast – curing needs warm, airy conditions
A sheltered, ventilated space – a greenhouse bench, a covered porch, or a shed with the door open
Netting, slatted crates, or old tights – anything that lets air circulate around the drying bulbs
Scissors or secateurs – for trimming tops and roots once the onions are cured

Do not wash your onions. Water is the enemy of storage – you want them dry and dusty, not clean and damp.

Step-by-Step Guide

Step 1: Know When to Harvest Onions

The clearest sign that onions are ready is when about half to two-thirds of the tops have naturally bent over and flopped at the neck. This "neck fall" tells you the plant has stopped feeding the bulb and is winding down for the season. Across most of temperate Europe this happens from mid-July through August, though a cool, wet summer can push it into early September.

Resist the temptation to bend the tops over by hand to speed things up – that old allotment trick can bruise the neck and invite rot. Let the plant do it on its own.

Step 2: Loosen and Lift the Bulbs

Once the tops have fallen, stop watering and wait for a dry spell. Slide a garden fork in a few centimetres away from each bulb and gently ease it upward to break the roots, then lift the onion out by hand. Work when the soil is dry so the bulbs come up clean.

Handle them like eggs. Bruises and nicks are exactly where rot starts, so avoid throwing them into a bucket or dropping them onto hard ground.

Step 3: Cure the Onions

Curing is the step that decides how long your onions keep, and it is the one most people skip. Lay the lifted onions in a single layer somewhere warm, dry, and well ventilated – on netting, a slatted bench, or a wire rack so air reaches all sides. In a reliable summer you can cure them outdoors in the sun for a few days, but bring them under cover if rain threatens.

Leave them for two to three weeks. They are fully cured when the necks are completely dry and papery, the outer skins rustle, and the roots have shrivelled. This is what seals the bulb and lets it store for months rather than weeks.

Step 4: Trim and Sort

Once cured, trim the roots off close to the base and cut the tops down to about 2–3 cm – or, if you fancy it, leave the tops on and plait them into a traditional string. Sort as you go: set aside any onion that is soft, thick-necked, or damaged. Those will not keep, so move them to the kitchen and use them first.

The neck test

A thick, soft, or still-green neck means that onion will rot in storage. Only firm, dry-necked bulbs go into the store – everything else goes on the chopping board this month.

Step 5: Store in a Cool, Dry, Dark Place

Store cured onions somewhere cool, dry, and dark with good airflow – an unheated pantry, a frost-free shed, or a garage all work well. The ideal is a cool 5–10 °C with low humidity. Use nets, slatted crates, or hung plaits so air keeps moving; never seal them in plastic bags, which trap moisture and cause rot.

Kept this way, well-cured storage onions will hold for anywhere from three to eight months depending on the variety. Check the store every few weeks and pull out any bulb that has gone soft before it spoils its neighbours.

Tips for Better Results

Choose storage varieties for the long haul. Firm, strong-flavoured storing types keep far longer than sweet, mild onions, which are best eaten fresh within a few weeks.
Ease off water before harvest. Stopping irrigation once the tops flop helps the skins firm up and cure faster.
Never cure in a damp shed. Poor airflow is the single most common reason a stored crop rots – ventilation matters more than warmth.
Keep onions away from potatoes. Potatoes give off moisture and gases that shorten onion storage life, so store the two crops separately.

Common Questions

Can I eat onions straight after harvesting?

Yes – freshly lifted onions are perfectly good to eat right away. They just will not keep. Any onion you want to store for the winter needs the full curing process first.

What do I do if it rains during curing?

Move the onions under cover immediately – a greenhouse, porch, or shed with the door open. Curing simply needs warmth and moving air, not direct sun, so a sheltered dry space works just as well and protects the crop from a wet spell.

Why are my onions rotting in storage?

The usual culprits are onions that were not fully cured, bulbs with thick or soft necks that should have been eaten fresh, or a damp, poorly ventilated store. Cure fully, sort strictly, and keep the air moving.

Next Steps

Harvesting the onion bed clears valuable ground right in the middle of the growing season, so do not let it sit empty. Late summer is prime time to follow on with a fast crop or a green manure – see our guide to what to plant in August for ideas, and think ahead with crop rotation so next year's alliums go into fresh ground. Plantory can map your beds, track what came out and when, and remind you what to sow next.

Plan Your Garden