When to Harvest Onions and Cure Them for Storage

You grew a good onion bed all summer, and then half the crop rotted in the shed by November. That is the most common onion story I hear from small growers, and it almost never starts in storage. It starts with when you harvest onions and how you treat them in the two or three weeks after they leave the ground.

This is the routine I use on a quarter acre market garden where onions fill about 600 row feet a year. It works for long day storage types like Copra and Patterson, and with a few changes for sweet onions that are never meant to keep.

How to tell when to harvest onions

An onion tells you it is done. When the bulb stops sizing, the neck just above it softens and the leaves fall over on their own. That is the signal, and it matters more than any date on the seed packet.

Watch for 50 to 80 percent tops down. Once at least half the bed has flopped, the crop is ready. Waiting until every last top is down invites rot in the early ones.
Check the necks. Pinch a few just above the bulb. A soft, hollow neck means the plant has finished moving sugar into the bulb.
Look at the outer skin. A dry, papery wrapper starting to form is a good sign. A wet, shiny skin means a few more days.

In most of zone 5 and 6, long day storage onions transplanted in April reach this point between late July and mid August. Short day types in the South finish in May or June.

Should you knock the tops down?

Some growers bend the tops over by hand to speed things up. I only do it for the last 20 percent of a bed when most plants have already fallen, so I can harvest the whole block on one dry day. Forcing tops down on onions that are still growing gives you smaller bulbs with thick necks that store poorly.

Lifting the crop without bruising it

Pick a stretch of weather with at least three dry days ahead. Wet soil sticks to the bulbs and feeds the molds that cause neck rot.

Stop irrigating about 7 to 10 days before you expect to lift. Dry soil releases the bulbs cleanly and starts the drying process in the ground.
Loosen each row with a broadfork or digging fork set 6 inches from the bulbs. On heavy clay, run it along both sides.
Pull by hand, holding the bulb rather than the leaves. Do not knock bulbs together to clean them. Every bruise is an entry point for rot.
Lay them in the row with the leaves of one row covering the bulbs of the next, so the bulbs do not sunscald in strong afternoon light.

If rain is forecast within a day, skip the field drying and move them straight to cover.

Curing onions so they keep

Curing is the step that turns a fresh onion into a storage onion. The neck dries and seals, the outer skins tighten into a protective wrapper, and the bulb loses a bit of water so it is less hospitable to rot.

The conditions that matter:

Temperature: 75 to 90 degrees F is ideal.
Air movement: constant. A box fan on low in a shed or barn makes a large difference.
Shade: out of direct sun after the first day in the field.
Time: 2 to 3 weeks for storage types, sometimes 4 in humid weather.

I cure on old window screens laid across sawhorses, one layer deep, leaves still attached. A 3 by 6 foot screen holds about 40 pounds of medium bulbs. Greenhouses work well if you put up 50 percent shade cloth and leave both ends open.

How to know curing is finished

Roll the neck between your thumb and finger. A cured neck is dry all the way through, with no green tissue and no slippery feel. Then trim the tops to about 1 inch and the roots to a quarter inch. Brush off loose dirt, but do not peel away skins.

The counter-take: do not braid your whole crop

Onion braids look great in photos, and plenty of homestead advice treats braiding as the classic way to store onions. On a small farm I think it is mostly a mistake for anything beyond a few strings for the farmstand display.

Here is why. Braiding means leaving the leaves on, and leaves hold moisture longer than a trimmed neck. One soft onion in the middle of a braid spreads rot to its neighbors before you notice it. Braids also take 10 to 15 minutes each, which adds up to hours for a 300 pound harvest. Trimmed onions in mesh bags or slatted crates are faster to pack, easier to sort and much easier to inspect every two weeks.

Storage conditions that last into winter

Cured storage onions want cool, dry and dark:

Condition	Target	What goes wrong outside it
Temperature	32 to 40 degrees F	Above 45 F they sprout sooner
Humidity	60 to 70 percent	Above 75 percent they grow roots and mold
Light	Dark	Light triggers sprouting and greening
Airflow	Gentle and steady	Still air lets moisture pool between bulbs

Do not store onions next to potatoes. Potatoes give off moisture that pushes onion humidity too high, and onions give off gases that can make potatoes sprout. Keep them in separate rooms or at least on opposite walls with a fan running.

Good storage varieties like Copra, Patterson and Redwing kept this way often last until March. Sweet onions such as Walla Walla or Candy are best sold or eaten within 4 to 8 weeks no matter how well you cure them.

Planning next year's onion bed

Write down the date your tops went down, the weather at harvest and how many pounds came through storage sound. Three years of notes will tell you more than any chart. If you split onions into a short storage block for summer sales and a long storage block for winter, they fit well into a simple succession planting plan. And growing two or three onion varieties instead of one is the same logic behind why growing more than one crop is cheap insurance. For more planting schedules and harvest timing, browse our growing food guides.

Frequently asked questions

Can you harvest onions before the tops fall over?

Yes, but treat them as fresh onions rather than storage onions. Bulbs pulled with green, upright tops have thick necks that do not seal properly during curing. Use them within a few weeks or sell them as fresh bunching onions.

How long should onions dry before storing?

Plan on 2 to 3 weeks of curing in a warm, shaded, well ventilated space. In humid summers it can take closer to 4 weeks. They are ready when the necks are completely dry and the outer skins rustle when handled.

Why are my stored onions rotting from the neck?

Neck rot is usually caused by a fungus that enters through a neck that was not fully cured, or through bruises at harvest. Lifting in dry weather, handling bulbs gently and waiting until the necks are fully dry before trimming prevents most cases.