Lift onions once most of the tops have flopped over and yellowed. For onions set out in early spring, that usually means midsummer. Pull them on a dry day, then cure them in a warm, shaded, airy spot until the necks are tight and the skins turn papery. Only then do they belong in storage. Skip the curing and even a good keeper starts rotting from the neck. The rest of the job is holding them at the right temperature and humidity, which is where most home storage goes wrong. For the full growing picture, start with Onions in West Virginia.
Keeping them, and for how long
A cured onion is a living bulb that has gone dormant, and storage is about keeping it asleep. Too warm and it sprouts. Too damp and the skins mold and the necks soften. Too cold and the flesh is damaged. Clemson Cooperative Extension’s Home & Garden Information Center says ideal conditions for onions are between 45 °F and 55 °F, and 50 to 60 percent humidity (Clemson Home & Garden Information Center). If you write down only one line, make it this one: 45 to 55 °F with 50 to 60 percent humidity.
Notice the humidity. Onions want dry air, the opposite of carrots, beets and other roots that keep best in a cold, damp cellar. One cellar corner can’t hold both crops well. If you grow both, give the onions their own spot.
How long do stored onions last?
Longer than most vegetables, but treat any duration as a ceiling reached only under ideal conditions. Pungent, well-cured onions held in that temperature and humidity range can carry a household well into winter. In northern gardens that grow long-day types, they can last into March. A bulb with a bruise, a wet neck or a thick, green center will not make it that far, and neither will onions in a room that runs warm. Check the pile every couple of weeks and pull out any bulb that has gone soft or smells sour, because one rotting onion spoils its neighbors.
Damage in the field often shows up later in the bin. Bulbs chewed by insects or scarred at the neck rot first, so sort them out at harvest. What Eats Onion in West Virginia, and When covers what to watch for during the season.
Why do sweet onions spoil sooner than pungent ones?
The bite of an onion comes from volatile sulfur compounds, and those same compounds help protect the bulb in storage. A sweet variety carries fewer of them. It tastes better raw and gives up sooner in the bin. The University of Missouri Extension (G6355) puts it plainly: “As a rule, ‘sweet’ onions do not store as well as the more pungent types.” No amount of careful handling turns a sweet onion into a winter keeper.
Day length lines up with this trade-off. A short-day variety starts bulbing at about 12 hours of daylight, according to Clemson Extension. Charleston sits at 38.38 degrees north and gets 14 h 41 of daylight on the longest day of the year. Short-day types therefore bulb early here, run sweeter and are best eaten first. Long-day types wait for 14 to 16 hours of daylight, keep longer, and bulb late at this latitude. That latitude belongs to Charleston. If you garden in the Northern Panhandle or the Eastern Panhandle, or down in the far southern counties, look up your own latitude, since the days run longer to the north and shorter to the south. The Best Onion Varieties for West Virginia sorts varieties by exactly this split.
Where in the house that actually is
A household fridge sits well below 45 °F, and the crisper drawer is humid on top of that. Whole onions kept there go soft and sprout, so the fridge is for cut halves in a sealed container. A heated room is the opposite problem. Kitchen counters and pantries on an interior wall usually run in the 60s or 70s, which is too warm and wakes the bulbs up.
The garage looks tempting because it is out of the way, but it swings with the weather. It can sit in the 80s on a warm September afternoon and drop below freezing in a January cold snap. Frozen onions turn to mush when they thaw. A shed has the same trouble.
The room that usually comes closest in West Virginia is a cool, unheated corner of the basement, away from the furnace and water heater. A north-facing closet or an unused back bedroom with the vent shut can work too. Humidity is the usual snag, because basements in a state with muggy summers often run damp. Damp air above 60 percent breeds mold on the skins and rots necks.
Before you commit a room, put a thermometer with a humidity readout there for several days and read it morning and evening. Skipping that check means you find out the room is wrong only when the bin starts to smell. A cheap digital gauge costs far less than a winter’s worth of lost onions. If the reading runs high, a small dehumidifier or a fan keeps air moving. If it runs warm, look for a lower, cooler spot.
Once you have the room, how you pack matters. Use mesh bags, slatted crates or old nylon stockings with a knot between bulbs, so air moves around each one. Avoid sealed plastic. Keep the onions away from potatoes and from any roots stored damp, since moisture and ripening gases from neighbors shorten their life.
Common questions
How do I know when onions are ready to lift?
Watch the tops. When most of them have fallen over on their own and begun to yellow, the bulbs have stopped growing. The necks go soft and the outer skins start to dry. Lift on a dry day with a garden fork, loosening the soil beside the row so you don’t bruise the bulbs. Handle them gently, since a bruised bulb rots first.
How do I cure onions?
Spread the bulbs in a single layer, tops still attached, in a warm, shaded spot with moving air, such as a covered porch, a barn aisle or a garage with the door open. Keep them out of direct sun, which can scald the bulbs, and out of rain. They are cured when the necks are tight and the skins are papery and rustle in your hand. Then trim the roots, cut the tops to a short stub of neck and brush off loose dirt. Don’t wash them.
What if it rains during harvest?
Lift the onions anyway if the tops are down, because they will not improve in wet soil. Bring them under cover and set them out where air can pass through, using a box fan if needed. Wet bulbs that sit in a closed space rot at the neck, so give them extra time and check them daily. Don’t put onions into storage until they are fully dry.
Which onions should I eat first?
Eat sweet varieties first, since they have the fewest protective sulfur compounds and will not last the winter. After them, use any bulb with a thick neck, a soft spot or damaged skin. Late nitrogen feeding is a common cause of thick necks, because it keeps the tops green and the neck wide open. Reserve the tight-necked, hard, pungent bulbs for the back of the bin. They are the ones that stay good longest.