The one thing that determines if your onions last three weeks or six months after harvest

A crate of homegrown onions can be gold in October and grey mush by November. The difference between triumph and rot rarely looks obvious on the day you pull them. Yet every grower I’ve met swears there’s a single choice that decides the whole winter.

I’m standing in a dim shed, the kind with a nail for every tool and a smell you can’t fake. Strings of onions tap the wall when the wind nudges the door, their papery coats making that dry, friendly whisper. We’ve all had that moment when you reach for an onion and find softness where you wanted snap. The shed remembers those, too.

Years ago, my neighbour in Yorkshire showed me two lots side by side: one batch crisp into spring, the other gone by Bonfire Night. Same soil. Same rain. Same hands. This is that decision.

The thin line between three weeks and six months

The one thing is this: the state of the neck. If the neck dries into a tight seal, the bulb can rest for months. If the neck stays juicy, it becomes a wick for rot and the onion breathes itself empty. Think of the neck as the doorway between the world and the heart of the bulb. Close it, you keep the house warm. Leave it ajar, and winter walks in.

I watched a plot-holder called Joe harvest in late August. Batch A: lifted when 70% of tops had fallen, laid in a single layer on wire racks in his greenhouse with a small fan humming. Fourteen days later the necks were crisp and the skins rattled. He trimmed to two centimetres and moved them to a cool, dark cupboard. They kept until March. Batch B: pulled a week earlier, thick green necks, piled in a crate in the garage “to sort next week.” Half had neck rot within three weeks, the rest sprouted by Christmas.

Here’s the logic. Onions are living reservoirs, still respiring after harvest. A wet, open neck speeds respiration and invites pathogens like Botrytis straight into the core. A dry, sealed neck slows the bulb’s metabolism and builds an armour of outer skins. You influence that with curing: air, warmth, time. You’re not changing the onion’s DNA. You’re changing the conditions that decide whether microbes get an easy motorway or meet a shut gate.

How to cure onions for six-month storage

Lift onions when most tops have flopped and the skins have coloured. Choose a dry day. Loosen with a fork, don’t yank by the leaves. Brush off soil, leave the roots on, and don’t wash. Lay bulbs in a single layer somewhere airy and shaded: a shed with a window, a carport, a greenhouse with the door open. Aim for steady warmth and moving air. Two to three weeks is the usual window. The neck is done when it twists without oozing and the outer layers are fully papery. Trim the tops to 2–3 cm or braid the whole lot if you fancy.

Heat helps, not sun. Direct sun can scald and toughen the wrong layers. A cheap clip-on fan is worth its plug socket. Rotate the trays every few days so edges don’t hog the breeze. Don’t crowd, don’t stack, don’t bag. Sort as you go: any nicks, soft spots, or thick “bull necks” are kitchen-first, not storage candidates. Store the sound bulbs in a cool, dark place with good air movement. Near-freezing works for pungent keepers; a cold pantry or unheated spare room is fine in a British winter.

Let’s be honest: no one does this every day. Life barges in, weather flips, and you improvise. That’s why a simple rule saves seasons.

“I stopped losing onions the year I got fussy about the necks,” Maggie in Norfolk told me. “Once they snap dry, they’re basically asleep.”

• Neck feels thin and papery, not cool or fleshy.
• Outer skins rattle and show even colour.
• Root plate is dry and corky, not moist or white.
• No bruises, cuts, or sunken patches.

The long view

What you’re really doing when you cure onions is setting a pace. You slow a living thing to a murmur so it can carry you through the lean months. That feels old-fashioned in the best way. A shed, a fan, a fortnight of patience, and food waste falls off a cliff.

Some varieties are sprinters and some are marathoners, yes. Sweet onions rarely last far beyond New Year. Sturdy storage types will see you to spring. Yet I’ve tasted both at their best thanks to the same moment of attention. You choose whether the neck becomes a lock or a leak. That choice ripples through your winter cooking, your budget, your sense of being set up.

Share what worked on your street or your allotment. Tell someone how you rigged a clothes horse and a desk fan and beat the damp. The trick isn’t fancy; it just asks for noticing. And that has a way of improving more than onions.

FAQ :

• What temperature is best for curing onions?Room-warm with moving air works well. Aim for a dry, shaded space around 18–27°C with a fan, not direct sun.
• Can I cure onions in a flat or on a balcony?Yes. Use a wire rack or clothes horse, keep them under cover, and add a small fan. A spare room with a window cracked open is ideal.
• How do I know the neck is truly dry?Twist it. It should feel thin and rustly with no cool moisture inside. The outer skins should rattle, and the root plate should be corky.
• Should I trim roots and tops before curing?Leave both on during curing. Trim roots and cut tops to 2–3 cm only once the neck is fully dry, or braid the dried tops.
• How should I store onions after curing?Cool, dark, and airy. Slatted crates, mesh bags, or braided strings. Keep them away from potatoes and fruit, and avoid plastic bags.