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Even though onions are cheap enough to buy by the bagful, for the greatest variety, you have to grow your own—and it’s not difficult to do. Here are some onion planting, growing, and harvesting tips!
Sure, we could just buy onion sets and plant those but there is not a wide choice of varieties available as sets—mostly 'Stuttgarter' or 'Ebenezer' and often they form a thick-necked onion that wants to go to seed instead of forming nice, firm bulbs.
Which Onion is Right for You?
Determining whether to start with onion sets, seeds, or plants depends somewhat on what is available to you. Here’s a primer:
Onion sets are tiny onions that will become full-size onions in about 14 weeks. Look for small sets no bigger than three-quarters of an inch in diameter. Larger ones often produce onions with thick necks that tend to go to seed. The choice of varieties is limited; two common ones are ‘Stuttgarter’, a flavorful, semiflat, yellow onion that grows and stores well, and ‘Ebenezer’.
Onions grown from seed keep well and are less likely to go to seed. Here you also get the widest range of varieties: red, yellow, or white; round, flat, or long; mild and sweet or pungent and tangy. Onion seeds should be started indoors, as they need soil temperatures above 50°F to germinate.
Onion plants are limited to the offerings at your local gardening center and some mail-order services.
Onion seeds need to be started indoors in cold climates like mine (Zone 5). We plant 2 seeds per cell and grow them inside until the weather has warmed up enough to plant them outside. It is easier to separate two plants and transplant them than if we started the seeds in a crowded community flat and had to tease lots of plants apart before planting them outside.
Long Day or Short Day Onions?
Onions are photoperiodic, which means they are sensitive to the amount of daylight they receive. When days last 12 hours or more, leaf production stops and bulbs begin to form. Since the farther north you go the longer days are in the summer, different varieties of onions have been bred for different parts of the country. Should you plant long day or short day onions? Imagine a line running across the country from the border between North and South Carolina to San Francisco (roughly 36 degrees latitude). If you live north of that line, plant long day types; south of that line, short day onions will do best for you.
Long Day Onion Varieties
Some good long day onions are:
'Walla-Walla' or 'Ailsa Craig' if you want huge onions.
'Red Wing', 'Red Florence', or 'Southport Red' are good reds.
'Copra', 'Yellow Globe' or 'Sweet Sandwich' are good keepers.
Short Day Onion Varieties
A few good short day onions are:
'Yellow Granex' for sweet Vidalia-type onions.
'Texas 1015-Y Supersweet' or 'Red Creole' store well.
'White Bermuda' for a mild onion.
What About Day-Neutral Onion Varieties?
Day-neutral onions don't care about day length and will produce an excellent crop in any part of the country. Some catalogs refer to them as intermediates.
Some good day-neutrals are:
'Super Star' is a mild white that produces large, sweet bulbs.
'Candy' is a yellow that stores well. It can grow to be softball-sized.
'Red Stockton' is a large, globe-shaped red that also stores well.
All onions appreciate an early start since temperature and day-length trigger bulb formation. Cool weather encourages heavy leaf growth so it is important to get your onions growing before warm weather hits. Young onion plants will not be harmed by light frost.
In the South, onions can be planted in the fall and overwintered to give them a headstart on the growing season. Since they continue to grow throughout the winter, they will be ready for harvest in May.
Onions prefer sweet fertile soil with near neutral pH and need lots of sunshine. The sulfur that gives them their bite comes from sulfur in the soil. Since they are shallow rooted plants, keep them well weeded and use mulch to keep the soil cool and moist. Onions grow best if planted where lettuce or squash grew the previous year but do poorly if they follow a cole crop.
How do you know when to harvest onions?
When the onions’ tops begin to dry out and fall over, push them all over and withhold water for about 1 week. Pull the onions and spread them out in the sun to allow the foliage to dry and the skin to toughen up, and they will keep better. If it is rainy, let them dry in a protected place such as a shed, garage, or barn.
Once cured, they can be hung in a mesh bag, spread no more than two deep in a box, or braided and hung in a cool (40° to 60°F), dry, well-ventilated area. Check periodically for sprouting or rotting onions and remove them. Do not store them in the refrigerator; it is too damp.
Sweet onions do not keep well because they have a high water content. To avoid bruising, store them so that they don’t touch each other. One way to do this is to use clean old panty hose. Slip in the onions one at a time, tying a knot between each one. Hang them in a cool, dry place.
In the Middle Ages, it was believed that onion juice could cure baldness, snakebite, and rabies. We can’t vouch for this, but we can promise that onions will add flavor to your food. No good cook should be without them!