Why are my onion tops falling over?

How to tell if it's normal

Check two things: timing and the bulb. Bulbing onions finish by letting their tops soften at the neck and fall over, usually after the bulbs have swelled and the outer leaves begin to yellow. If that's what you see across most of the row, the plants are done growing and moving toward dormancy. Tops that flop while the bulbs are still small, or plants that yellow, wilt and come out of the ground with almost no tug, have something else going on. Pull one suspect plant and look at the roots, the base and the leaves.

When it's maturity

Falling tops at the end of the season are a good sign. Nebraska Extension suggests harvesting when about two-thirds of the tops have fallen over and dried naturally and the necks have started to shrivel; many gardeners start once half have fallen. Don't bend green tops down to speed things up. Nebraska notes this only cuts bulb growth short, because the green leaves are still making the sugars stored in the bulb. Once most tops are down, lift the onions within a week or two, before bulbs start to rot or regrow.

When it's pests or rot

Onion thrips are tiny, slender insects that rasp the leaf surface, leaving silvery streaks and black specks of droppings, often deep in the leaf folds. Heavy feeding in hot, dry weather can make leaves wither from the tips and flop early. Onion maggots work below ground. University of Minnesota Extension describes plants that yellow and wilt, sometimes rapidly, with holes in the bulbs and cream-colored, legless maggots inside. Damage often runs along a short stretch of row, and soft rot can follow the wounds, leaving a soft, foul-smelling bulb.

Rots are the other early-collapse cause. Minnesota lists Fusarium basal rot, where leaves yellow from the tip down and the bulb has a watery brown decay starting at the base, often with roots rotted away so the plant lifts out with little resistance. Pink root turns roots dark pink to maroon and leaves bulbs small. Neck rot usually shows up later, in storage, as a soft, sunken neck with gray mold. It is most common in onions that were bruised at harvest, had thick necks, or weren't fully cured.

What to do now

If the tops fell from maturity, loosen the soil with a fork and lift the bulbs gently, then cure them in a warm, dry, airy spot out of direct sun. Nebraska suggests 75–90°F for 2–4 weeks, until the necks and outer skins are dry and papery. Use thick-necked or bruised bulbs soon rather than storing them. If pests or rot caused the collapse, pull affected plants, use sound bulbs first, and don't compost rotten ones. For thrips, a hard spray of water can knock numbers down; insecticidal soap can help too, but not above 90°F or on drought-stressed plants.

Next season

Next year, plant onions where no onions, garlic or leeks have grown for the past few years, and start with firm, healthy sets or transplants. Row cover from planting time can keep onion maggot flies from laying eggs at the base of the plants. Keep the soil evenly moist during hot spells, when thrips build up fastest, and finish nitrogen feeding before bulbs start to swell so the necks dry down well at harvest.