Best Storage Onion Varieties
Properly stored, onions can last for months. The best storage onion varieties have a high sulfur content—they’ll really make you cry—and they have a strong flavor. Mild-flavored or sweet onion varieties will likely only keep for a few weeks. ‘Stuttgarter’, ‘Yellow Globe’, ‘Copra’, ‘Patterson’, ‘Redwing’, and ‘Ebenezer’ are a few storage varieties. Check with your local cooperative extension office to find out which varieties will grow best in your area.
When to Harvest Onions
A good rule of thumb is to harvest onions when about half the leaves have died back. As onions approach maturity, “they start accumulating water and sugars in the bulbs and pulling sugars and nutrients from the leaves into the bulbs, which causes the leaves to die back and the tops to flop over,” says Genevieve Higgins, Extension Vegetable Production Educator at the University of Massachusetts. But Higgins cautions, “Don’t wait until the foliage on every plant has fallen, or you run the risk of the plants that matured earlier becoming over-mature.” Use a garden fork to loosen the soil around your plants, taking care not to skewer the onions. Then lift your onion bulbs out of the soil and brush off the excess dirt. If the soil is loose already, you can simply pull them up by hand. Do not remove the leaves. “It’s best to leave the tops on onions until they are fully cured. Cutting off the tops before the neck is cured down provides an entry point for bacteria and fungi, which can lead to bulb rots,” says Higgins. Any onions that have flowers should be used as soon as possible; they will not store well.
Curing Onions
Proper curing is critical for onion storage: the outer layers of the bulb need to dry sufficiently to protect the interior portion of the bulb from rot and mildew. In dry weather they can be cured outside by simply laying them on top of the soil or a clean dry surface. Don’t wash them, just brush off loose dirt. “Be careful not to leave onions out in excessive heat or in excessive moisture. Moderate warm and dry conditions are helpful when curing, so if it’s nice and sunny out, let them dry where they are. Excessive exposure to moisture or sun in the curing process could lead to decay or collapsed layers,” says René Hardwick, director of public and industry relations for the National Onion Association. Alternatively, onions can be cured in a garage, shed, or covered porch where they’re protected from wet weather. “The goal is to achieve dry conditions and temperatures below 85℉ for two to four weeks. Make sure whatever structure you’re curing your onions in has good air flow and ventilation. Open doors and use fans to move air around,” says Higgins. You can tell when your onions are well cured when the outer skin layers dry to the point of making a rustling sound when they’re moved. “The necks of onions should dry down so that when you pinch the neck between your thumb and pointer finger, it feels dry and not slippery inside,” says Higgins. When cured, brush off any remaining dirt and loose layers. Then cut the tops about an inch or so above the bulb (unless you want to braid the onions for storage), and trim the roots. Sort the onions and separate any that are damaged or haven’t cured sufficiently and use them right away (onion rings, anyone?).
How to Store Onions
“Ideal storage conditions for long-term storage is 32℉ with 65 to 70% relative humidity,” says Higgins. Although these conditions may be difficult to maintain at home, onions are pretty forgiving. “Often, storing cured onions in a barn or garage so that they cool down with the outside temperature is good enough,” says Higgins. But be sure to avoid high temperatures and exposure to sunlight, which will trigger sprouting. Be sure that your storage area is well ventilated. Storing your onions on trays or in open bins helps with air flow around the bulbs. Plus it makes it easy to keep an eye on them so you can quickly spot any that start to go bad or sprout. Alternatively, you can store them in a mesh bag, wire basket or crate, or braid them for hanging. Check them regularly and discard any that show signs of rot. Don’t store onions near potatoes or apples. Spuds and apples can give off high levels of ethylene gas (a natural plant hormone), which can trigger spouting. When you have a good harvest, it’s well worth the effort to cure and store your onions properly so you can continue to enjoy them for many months.
