What curing actually does
Curing is not drying the crop out. It is a short, controlled period in which the outer layers lose moisture and the skin hardens and seals, while the flesh inside stays exactly as wet as it was. That sealed skin is the barrier that keeps water in and rot organisms out for the following six months.
Two things happen during it. Existing minor wounds — scuffs, stem scars, the cut where you severed the vine — suberize, which is to say they scab over with a corky layer. And the skin itself thickens and toughens. Skip curing and you are storing produce with an open wound and a permeable surface, which is why uncured squash goes soft in weeks and cured squash keeps until spring.
Every crop below wants warmth, air movement and time. What varies is how much of each, and whether it wants humidity or dryness.
The greenhouse is the right room for the wrong part of the year.
September and October give you exactly what curing needs: daytime warmth, good airflow, easy access. December gives you a space that swings twenty degrees between noon and midnight and drops below freezing, which is close to the worst storage environment available. Cure under glass, then move everything out.
Winter squash and pumpkins
Harvest when the skin is hard enough that a thumbnail will not dent it, the stem has started to dry and cork, and the ground spot has turned from white to cream or orange. Cut with a good length of stem attached — several inches — and never carry a squash by the stem. If the stem pulls out you have an open wound at the worst possible place and that fruit goes to the kitchen, not the store.
Cure warm and fairly humid for about ten days to two weeks. A greenhouse bench in early autumn is close to ideal. Space the fruit so nothing touches, and get air underneath — a wire rack or slatted bench, not a solid shelf, as covered in curing and drying racks. Turn them once midway.
Exceptions. Acorn squash and most delicata types do not want curing at all; warm curing shortens their life rather than extending it. Wipe them clean and store cool from the start.
Store cool but not cold, dry, and dark, in a single layer if you can. Check monthly and use anything with a soft spot immediately.
Onions and shallots
Harvest when about three quarters of the tops have flopped over naturally. Do not bend them over yourself; the plant is moving resources down and interrupting that shortens storage life. Lift on a dry day and leave them on the surface for a few hours if the weather allows.
Cure with the tops still on, for two to three weeks, until the necks are completely dry and papery and the outer skins rustle. This is the step people cut short. Squeeze the neck: any softness at all means it is not done, and a soft neck is a direct route for rot into the bulb.
Single layer on mesh, or tied and hung in the roof space. Do not heap them, do not leave them in the sun where they will scald, and keep air moving.
Trim after curing, not before: cut the tops to about an inch, and the roots close but not into the base plate. Or leave the tops on and braid them.
Store cool, dark and dry, in paper sacks, nets or open crates. Any bulb with a thick or soft neck goes to the kitchen first — those never keep.
Garlic
Harvest when the lower few leaves have browned but several green ones remain. Each leaf corresponds to a wrapper layer around the bulb, so waiting for all of them to die means harvesting a bulb with no intact wrappers, which will not store.
Do not wash the bulbs. Brush soil off once dry. Washing drives water into the wrappers, which is exactly the tissue you need intact and dry.
Cure for three to four weeks in small bundles hung in a shaded, airy spot, or single-layer on mesh. Longer than onions, and more sensitive to direct sun — scalded garlic does not keep. Done when the wrappers are papery and the neck is fully dry.
Store cool and dry, and keep some back for planting. If you are replanting your own, the largest bulbs from the best plants go into the October sowing window, not into the kitchen.
Where it goes wrong
Stopping too early
By a wide margin the commonest failure. Onions that look dry on the outside often have a neck that is still soft, and a soft neck lets rot in weeks later, when the crop is in a sack and nobody is looking. Squeeze the neck before you commit.
Curing in a heap
The outside cures, the middle stays wet, and the middle is where the rot starts. Single layer, every time, or hung.
Direct sun
A greenhouse bench in full midday sun scalds onions and garlic. Cure in the brightest part of the house that is not in direct beam, or shade the bench.
Leaving it in the greenhouse too long
Cured produce left under glass into November gets a nightly freeze-thaw cycle that ruins it. Move it out as soon as curing finishes, and read that as a hard deadline rather than a suggestion.
Storing damaged with sound
Anything bruised, cut, thick-necked or soft goes to the kitchen. One rotting bulb in a sack takes several with it, and you will not notice until you open the sack in January.
The humidity you are creating
A full curing load puts a great deal of water into a small volume of air, at the same time of year that the greenhouse is already producing condensation. Keep a vent open and a fan running through the curing period, or you will cure the crop and grow gray mold on everything else — see autumn condensation and gray mold.
What helps
Hanging drying nets
$ · Onions and garlic · uses roof volume, gives total air access
Multi-tier mesh nets hung from the ridge are the traditional answer because they work: air on every side, no contact points, and they use the vertical space a greenhouse has spare in autumn. Collapse flat for storage the rest of the year.
Paper storage sacks
$ · After curing · breathable and dark
Thick paper sacks exclude light without excluding air, which is exactly what cured alliums need. Cheap, stackable, and far better than any sealed container. Label them, because a sack of onions and a sack of shallots look identical in February.
Small circulation fan
$ · Through the curing period · moves the moisture you are releasing
A curing load releases a lot of water into a small volume. A fan moving air across the racks speeds curing and keeps the humidity from settling on everything else in the house. Run it alongside an open vent, not instead of one.
The curing calendar
| Crop | Cure for | Conditions | Done when |
|---|---|---|---|
| Winter squash | 10–14 days | Warm, humid, airy, spaced | Skin resists a thumbnail; stem corked |
| Acorn / delicata | Do not cure | Cool from the start | — |
| Onions | 2–3 weeks | Warm, dry, airy, out of direct sun | Necks fully dry; skins rustle |
| Shallots | 2–3 weeks | As onions | As onions |
| Garlic | 3–4 weeks | Shaded, airy, never washed | Wrappers papery; neck dry |
| Potatoes | ~2 weeks | Cool, dark, humid | Skins set; then dark store |
Once curing is finished the bench is free, which is convenient timing — it is roughly when dahlia and canna tubers come in to be dried and packed. See bulb and tuber storage.
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Common questions
How long does winter squash need to cure?
Around ten days to two weeks, warm and airy, with the fruit spaced so nothing touches and air can reach underneath. Acorn and most delicata types are the exception — warm curing shortens their storage life, so wipe them clean and store cool from the start.
Why do my onions rot in storage?
Almost always because curing stopped too early. Onions that look dry outside often still have a soft neck, and a soft neck is a direct route for rot into the bulb weeks later. Squeeze the neck before you commit them to a sack: any softness at all means keep curing.
Should I wash garlic before storing it?
No. Washing drives water into the wrapper layers, which is exactly the tissue that needs to stay intact and dry for the bulb to keep. Let the soil dry and brush it off. Cure for three to four weeks in a shaded, airy spot until the wrappers are papery.
When should I harvest garlic?
When the lower few leaves have browned but several green leaves remain. Each leaf corresponds to a wrapper layer around the bulb, so waiting until all the leaves die gives you a bulb with no intact wrappers, which will not store.
Can I leave cured produce in the greenhouse over winter?
No. Once curing is finished it needs to move to a cool, dark, stable store. A greenhouse in late autumn swings widely between day and night and freezes overnight, and the freeze-thaw cycle ruins produce that cured perfectly well a month earlier.