Onions can be confusing for new gardeners. Should you grow long-day or short-day onions? Does it make a difference whether you grow them from seeds, seedlings or sets? How are storage onions different from sweet onions? Here's how to sort out the terms.
Day length refers to the number of hours of daylight, from sunrise to sunset. It increases from Dec. 21 to June 21, which is the longest day of the year. Day length triggers onion plants to begin developing bulbs.
Onions are biennial plants, which means that they sprout from a seed and grow a bulb their first year. That's when bulbs are usually harvested. If left in the ground, the plant goes dormant for the winter and sprouts again in the spring. In its second season, however, the plant puts most of its energy into producing a flower and making seeds instead of a bulb.
Onions can be grown from any of these life stages: seed, seedling or dormant bulb. Here's how to choose which ones to grow.
Onions are mature and ready to harvest when their tops flop over. Pull up the bulb and let the whole plant dry slowly in a well-ventilated, dark place, up to several weeks. Once the stems have withered and the onions are completely dry, they can be moved indoors to a cool, dark location for storage. Some varieties may be stored for up to eight months, so with careful planning (and enough garden space) you can be eating homegrown onions all year round. For more information, read How to Harvest, Cure and Store Onions.
Scallions, also known as green onions or bunching onions, are young onions that have not formed bulbs. You can sow them much closer together — as little as an inch apart. Most varieties will work, but it's best to choose those that are especially suited to growing as scallions. Ideally they should be mild and sweet.
Harvest them as needed. Store in the refrigerator for up to a week.
Depending on their variety and the soil in which they grew, onion bulbs contain differing levels of water, sugars and sulfur compounds. The amount of sulfur the bulb picks up from the soil will determine how pungent or tear-producing the onion will be and also how long it will keep in storage. Some varieties will keep in storage for months while others are best when used within weeks of harvest. You'll find this kind of information on the seed packet. One way to "store" onions that aren't good keepers: Make caramelized onions.
How to harvest, cure and store onions
Making caramelized onions
Storage techniques for "keeper crops"
Recipes for savory tarts
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