While tomatoes and potatoes are often in the garden limelight, onions (Allium cepa) and other members of the allium family, are more widely used in cuisines around the world. They’re easy to grow, easy to store, good for you and delicious to eat. Originating in Asia and the Middle East, they’ve been cultivated for more than 5,000 years, are used for both food and medicine, and include hundreds of species—some are purely ornamental and make striking displays in our gardens, while others we use every day in our kitchens.
Onions come in a variety of shapes and colors: globe, flattened disks (cipollini) and torpedoes, and in various shades of red, yellow and white. They range in size from tiny boilers less than 1 inch in circumference to the whopping 5-pound Ailsa Craig, a sweet globe-shaped heirloom variety.
Onions are classified by flavor (sweet or hot) and light requirements. According to the Penn State Extension, several factors can affect their sweetness, the main measure being variety, though climate and soil composition also play a role. Sweeter onions should be grown in consistently irrigated soil with naturally low sulfur levels, and should be harvested in moderate temperatures. Evenly spaced, less-dense plantings will result in less-pungent crops.
Light requirements for onions are broken down into two categories: long-day, needing 13 to 16 hours of sunlight to form bulbs, or short-day, needing 10 to 12 hours of sunlight to form bulbs. Plant short-day varieties in southern states and long-day onions in the North.
To grow all onion varieties, choose a plot in full sun, and pay close attention to soil preparations. Onions prefer pH levels between 6.0 and 6.8. Dig compost or aged manure into the bed in fall to break down over winter and be ready for early spring planting. Planting in raised beds is ideal because they have good drainage. Onion tops grow in cool weather, and the bulbs develop when the weather turns warm, so you can plant onions as soon as the soil is workable in spring.
Begin the onion plot one of three ways: seeds, transplants or sets. Seeds require the longest grow time—four months from seed to bulb—but give you the greatest number of variety options. Start the seeds indoors under artificial light about two months before you transplant them into the garden. Transplants (aka young seedlings) and sets (aka small bulbs) are the easiest to plant and the earliest to harvest. They are available from local garden centers or through mail-order catalogs.
Mix a 2-inch layer of compost over the row, and plant the sets 2 inches deep and transplants 1 inch deep, so the roots are covered but not too high up the leaves. Space plants 4 to 6 inches apart to give them plenty of room to mature. At time of planting, use a liquid organic fertilizer according to the directions on the bottle to get them off to a good start, and repeat when bulbs start to form.
Keep onions watered and weed-free to encourage large bulbs. As they start to mature, pull the soil away to expose the bulbs. The sun and air will help thicken the outer skin to ensure better storage.
When the green tops wither and start to turn brown, the onions have matured and are beginning to go dormant. Once most of the tops are brown, tip over each whole onion to break the roots. When soil is dry, gently lift the onions from the ground by pulling or using a fork to avoid bruising. Lay in a single layer on a screen in a warm (75 to 80 degrees F), airy spot to cure for about three weeks.
Sweet onions can be stored for a couple months in a cool, dry and dark place, such as the crisper drawer of your refrigerator or a root cellar. They have thinner, paler skin than hot onions with a variety of names, including Spanish, Walla Walla, Bermuda and Vidalia. (Only onions grown in a 20-county region in Georgia are distinguished as Vidalia onions, but they’re shipped to consumers around the world.)
Hot varieties, which have more pungent flavors, store better because they develop thicker tough layers on the outside. Hot varieties include Copra, Stuttgarter and Yellow Globe. Store hot onions at 40 to 50 degrees F in a dry, dark, well-ventilated area in baskets or mesh bags, or braid the stems and hang from the rafters. When ready to use, peel, chop and store in the refrigerator for up to a week or in the freezer for 10 to 12 months. Hot onions can also be dried in a dehydrator at 155 degrees F for eight to 10 hours (best done outdoors or in a garage, due to the pungent odor) and stored in canning jars for one to two years, but the equipment can be costly and requires more time to process than other storage methods.
Sweet onions can be eaten raw or slow-roasted to bring out their best qualities. High heat makes all onions bitter, so use medium to low heat, and don’t cut the onions until you’re ready to cook them, as their flavor deteriorates over time. A good rule of thumb when reading recipes: One medium onion equals 1 cup chopped.
Other Alliums to Rave About
While onions are a mainstay in most kitchens, other members of the allium family can add depth and interest to your meal preparations. Take a look at some other alliums to consider growing.
- Scallions (Allium fistulosum, Allium chinense, Allium x wakegi, Allium x proliferum)
Any onion can be pulled early and used as a scallion; however, there are specific varieties called bunching onions, or Welsh onions, that never form bulbs, which are more frequently used as scallions. Use in place of bulb onions for a milder flavor, or add raw to salads.
- Leeks (Allium porrum)
The perfect answer to a longer season of fresh onion flavor, leeks can withstand frost and be left in the ground until it freezes. Start indoors eight to 10 weeks before the average last frost, and plant as soon as the soil can be worked. Plant different varieties (early, middle and late season) at the same time in spring for a rolling harvest.
- Garlic (Allium sativum)
You’ll find two main subspecies of garlic: softneck and hardneck. Use the mature bulbs, or harvest young as green garlic and use like scallions, slicing the white part and tender greens. Scapes and green garlic are both milder than the mature bulbs.
- Shallots (Allium ascalonicum)
A favorite in France, shallots taken on a “fancy” onion status in the U.S. Like garlic, plant one bulb to grow a cluster. Related species include Egyptian (or walking) onions and multiplier onions, sometimes called potato onions. The flavor of shallots is sweeter, milder and a bit more complex than onions, and they are often paired with white wine, butter and cream.
This article was excerpted from the March/April 2014 issue of Hobby Farm Home.