When to Harvest Onions

The signs that bulbs are ready

When an onion finishes bulbing, the neck just above the bulb softens and the leaves fall over. That is the signal to watch for. Sources differ on how many tops should be down. Maryland Extension and NC State harvest when about two-thirds have fallen. Clemson and Virginia Tech wait for three-quarters. UF/IFAS, writing for Florida’s short-day crop, says harvest typically comes when about a quarter of the tops are down. In practice, start checking as soon as the first tops fall, and harvest the patch when most of it has gone over.

Virginia Tech adds a deadline: don’t wait more than one to two weeks after the tops fall. Tennessee Extension notes that mature bulbs left in wet ground lose quality.

Timing by region:

• Northern spring plantings mature in mid to late summer. Utah State expects about 100 to 120 days from seed, and says a crop seeded in spring gives storage bulbs in September. Overwintered onions in Utah mature in June or July.
• Southern fall plantings come out in late spring and early summer. Texas A&M expects fall-seeded or winter-transplanted onions to bulb from May into July.
• Sets take about 4 to 5 months (Rhode Island and Arizona calendars). UF/IFAS gives the same 4 to 5 months for Florida onions.

Before you dig

Ease off the water first. Utah State says to stop watering once the tops start falling, because a wet finish delays curing and causes storage rot. Clemson stops a week before harvest so the bulbs form their protective outer scales. Clemson also gradually pulls soil away from the bulbs over the last month. By 7 to 10 days before harvest, about a third of each bulb should sit above the soil, which speeds drying of the bulb and neck.

Lifting the bulbs

Pick a dry day. NC State recommends a garden fork, and Tennessee Extension suggests undercutting with a shovel, since pulling often fails once the leaves have dried down. Handle bulbs gently. Maryland and Virginia Tech both point out that bruises lead to storage rot.

Curing: the step that decides storage life

Curing dries the outer scales and seals the neck. Sources agree on the conditions: shade, dry air and good airflow, with no direct sun. The time they give varies:

• Utah State leaves the lifted bulbs in the garden for 1 to 2 weeks, with the tops shading them.
• Maryland Extension leaves them a few days in the garden, then moves them with tops on to a well-ventilated attic or porch for 1 to 2 weeks.
• NC State and Montana State allow 2 to 3 weeks.
• Texas A&M, writing for Texas heat, leaves bulbs on the ground only 1 to 2 days before removing the tops and drying them in baskets or boxes.

The onions are cured when the necks are dry and tight, the skins are papery and the roots are dry. Then trim the tops. Maryland cuts them to about 1 inch above the bulb, Clemson 1 to 1-1/2 inches, Utah State 1 to 2 inches and Tennessee around 2 inches. Thoroughly dried bulbs can also be braided by their tops instead.

Storing onions

Set aside bulbs with thick necks to eat first. They come from bolted plants or late nitrogen, and Clemson says they are hard to cure.

Sources split on storage temperature:

• Cold storage. Maryland Extension keeps bulbs at about 32°F and 65 to 70 percent humidity for up to 6 to 7 months. Utah State recommends 32 to 40°F and dry.
• Cool storage. Clemson and Virginia Tech recommend 45 to 55°F at 50 to 60 percent humidity. Virginia Tech expects 6 to 7 months.

Both groups agree that the onions must be dry and well ventilated. Maryland adds that warm storage makes bulbs sprout, while temperatures below freezing injure them. A cool basement or garage keeps onions in mesh bags or ventilated boxes for 2 months or more (Maryland). Montana State says not to store them in plastic bags.

The type of onion matters as much as the room. Northern long-day storage onions last longest. Sweet onions hold more water (UF/IFAS). Tennessee says short-day and intermediate onions store poorly, Clemson says the same of short-day types, and Montana State suggests refrigerating mild, high-water onions to extend their life. Utah State says its recommended varieties, sweet types included, keep about 2 to 4 months. Check stored onions regularly and use any that soften or sprout first.