Are you ready to plant? Dodging the snowstorms has been a little tricky, but spring will come. When it does, we will all think that we should have put in our gardens yesterday.
One of the earliest crops to go in the ground each year is onions.
Onions belong to the allium family that comprises some 600 species, including garlic, chives, scallions, leeks and flowering alliums.
Onions are an ancient crop. The pyramid builders in Egypt and Greek and Roman troops relished onions in their diets.
Onions are a diverse crop, and 26 states, including Utah, grow onions commercially. Growers across the country use more than 100 different varieties. Many of these are not available to home gardeners, but there are still plenty of good ones on the market for them.
Onions are named and classified based on flavor, color, bulb size, shape and use. They are further classified as storage, fresh, pearl or green onions.
They are also classified by an unusual characteristic. Unlike most garden vegetables, onions have a peculiar growth factor. They are sensitive to day length. The day length, or photoperiod, along with temperature, controls the bulb formation. Short-day varieties form bulbs when the day length is 12 hours or less.
Long-day plants form the best bulbs when there are 15 or more hours of daylight — when summer days are the longest. One common complaint of home gardeners is that their onions never produce big bulbs, but this is often because they plant short-day variety sets instead of long-day variety transplants or seeds.
Because the plants are sensitive to the photoperiod, some onion varieties are unsuitable for northern climates. That is because they begin to form bulbs when the plants are too small. Short day-length varieties are generally unsuitable for growing bulb onions in all but the southern parts of the United States. Long-day and a few intermediate-day varieties are usually grown in Utah.
Growing large, tasty onions takes more than just luck. Variety selection is absolutely critical because onions are either short- or long-day varieties. Long-day onions are best for our area, as they form larger bulbs here.
Onions adapt to a wide temperature range and tolerate frost. Getting them in the ground early when air temperatures of 55-75 F prevail lets the foliage and roots develop before bulbing starts.
Onion seeds are usually planted in the spring as soon as the soil can be tilled. This is often before the last frost on light, sandy soils. Planting them this early sometimes causes other problems, however. If the plants freeze hard, they often bolt, or send up flower stalks.
Bolting is more frequent on plants grown from sets or those exposed to temperatures below 45 degrees after the plants start growing. If flower stalks develop, cut them off immediately so the bulb size and quality will not be reduced, or salvage them by harvesting the bulbs. The process is not reversible once it has started.
Gardeners have the choice of growing their onions from seeds, transplants or sets. Seed-raised onions are the most important commercial crop because the ripe bulbs can be stored and shipped. Transplants allow earlier planting and also produce large bulbs.
Sets are an easy way to grow onions, but they may not give the best results. Sets have already been through one growing period and often go to seed instead of forming bulbs. Most sets are grown in the South and are short-day varieties not well adapted to this area.
Onions produce best when they are grown in full sun and fertile, well-drained soil. Incorporate organic matter and a fertilizer into the soil before planting. Plant seeds 1/4- to 1/2-inch deep in rows 8-16 inches apart. Place seeds, sets or transplants 3-4 inches apart in the row. If you plant them closer, thin the plants to the correct spacing and use the pulled plants as green onions.
After bulbing begins, you want a high temperature and low humidity through the harvest and curing period. Because they have a shallow root system, keep them well supplied with moisture. Light mulch added after the plants start to grow helps conserve moisture.
Some of the best homeowner varieties include Evergreen White Bunching, a good mild green onion. Utah Sweet Spanish, Fiesta, Walla Walla and Sweet Sandwich are excellent onions to grow for nice bulbs. Crystal White Wax is a nice pickling onion.
Onions are one crop you need not be without in your garden. Whether you are pulling tender green onions in the late spring or enjoying stored onions from the previous harvest, onions can be enjoyed throughout the year.
Larry A. Sagers is the horticulture specialist, Utah State University Extension at Thanksgiving Point.