When to Harvest Onions (Signs They're Ready)

Green onions and storage bulbs are two different harvests

Onions give you two crops off the same plant, and the timing splits in two.

Green onions (scallions) come early. Pull them young, once the tops reach about 6 to 8 inches, which Clemson Extension puts at roughly six to eight weeks from a set or transplant. No bulb needed.

Storage bulbs take the long road. They need the plant to size up a full bulb, then signal that it is done. That signal is the tops falling over.

The days-to-maturity figure shifts with your onion type. Short-day onions, grown in the South, bulb on about 12 hours of daylight and mature on the early side. Long-day onions, grown up North, wait for 14 or more hours of daylight before they bulb, per the University of Minnesota Extension. Treat the 90 to 110 day window as a starting point, not a stopwatch. The plant tells you the truth.

How to tell storage onions are ready

The onion shows you. Three signs line up when a bulb is mature.

• Tops flop over. When about half to three-fourths of the tops fall over on the soil, the bulbs are done sizing up. Clemson Extension points to roughly three-fourths down. Illinois Extension says harvest when most of the tops have fallen.
• Necks go soft. Pinch the neck just above the bulb. A mature onion's neck is soft and limp. A stiff neck means it is still growing.
• Skins turn papery. The outer scales dry into the thin, crackly skin you see on a store onion.

Wait for the tops to fall on their own. The Illinois Extension warns that bending them over early interrupts growth and gives you smaller bulbs that store poorly.

How to harvest

Once the tops are down, pick a dry day and lift.

1. Loosen the soil. Slide a spading fork under the bulbs and ease them up. Do not yank by the tops, which can tear the neck.
2. Lift the bulbs. Pull them by hand once the soil is loose.
3. Let them dry in place. Illinois Extension suggests leaving lifted onions in the garden a few hours so sun and wind dry the outsides. If rain is coming, move them straight to a covered, airy spot instead.

Keep the tops and roots on for now. You trim them after the cure, not before.

Curing and storage

Curing is what turns a fresh bulb into one that keeps for months. Skip it and your onions rot in the bin.

Spread the onions in a single layer in a warm, dry, shaded spot with good airflow. A garage, carport, or covered porch works. The University of Minnesota Extension calls for a warm (75°F to 90°F), well-ventilated area for two to four weeks, until the outer scales are dry and the neck is tight. Illinois Extension lists a similar 2 to 3 week cure, finished when all the tops are dry and brown.

When the necks are tight and the skins are papery, the onions are cured. Then:

• Trim the tops to about 1 to 2 inches above the bulb. Clemson Extension trims to roughly 1 to 1.5 inches.
• Trim the roots close to the base.
• Store cool and dry. Clemson puts storage at 45°F to 55°F. Keep them in mesh bags, slatted crates, or baskets in a dark, dry, cool place that will not freeze, per Illinois Extension.

The short version

Storage onions are ready when about half to three-fourths of the tops flop over and the necks go soft, usually around 90 to 110 days. Lift them on a dry day, cure for 2 to 4 weeks until the skins are papery, then trim and store cool and dry. Pull the thick-necked bulbs for the kitchen and keep only tight necks for the bin.

Harvesting other crops this season? Onions cure a lot like their cousin in the when to harvest garlic guide, and the same lift-and-cure patience pays off in when to harvest potatoes. Planning next year's bed? How far apart to plant onions has the spacing, when to plant onions covers timing, and how much compost do I need covers feeding the soil first.

How many plants fit your bed

When you replant, size the bed first. Run your dimensions through the calculator to see how many plants fit in square, triangular, and square-foot layouts.