Onion, a garden plant of the lily family, closely related to the leek, garlic, chive, and shallot. The bulb of the onion plant, also called onion, is widely used as a seasoning and is eaten as a vegetable. Although onions have little food value, they impart a desirable flavor to stews, soups, hamburgers, and other dishes.Onions come in distinct sizes, shapes and smells.
Onions are native to central Asia and have been cultivated for more than 4,000 years. They are raised throughout temperate and semitropical regions of the world. Onions are an important commercial crop in at least half of the states of the United States.
The onion plant consists of shallow roots, a bulb, and green, tubular leaves. Its bulb is made up of a small buttonlike stem from which the roots grow, and many concentric leaves that are adapted for food storage. The green leaves of the plant are extensions of the outer food-storage leaves. Onion bulbs range in shape from flat to globular to oblong, and usually are white, yellow, or red.
As an onion plant matures, it produces a tall seed stalk. In most varieties white or bluish flowers grow at the end of the stalk in a spherical cluster called an umbel. In some varieties, small bulblike structures called bulbils grow in the umbel.
Onions require moist, rich soil and a cool climate, and thrive in temperate regions as biennials. In semitropical areas they are raised as winter crops and are annuals in the long growing season.
If left to themselves, onions propagate in one of three ways:
- They produce seeds.
- The bulbils sprout roots and leaves when in contact with the ground.
- Bulblets (sections that split from the main bulb) sprout roots and leaves of their own.
Commercially, onions are raised from seed; from seedlings that are transplanted to the field; and from setsimmature bulbs that are harvested when half grown, and used for early spring planting.
Most onions are harvested when the bulbs are full grown and are sold as fresh bulb-onions. Some are gathered when immature and sold as green, or bunching, onions. These green onions are sometimes called scallions (as are the related shallots leeks). Other onions are pickled in brine and vinegar or are dried and marketed as onion flakes or onion powder.
There are both wild and cultivated onions. The nodding (or wild) onion, found in the United States, grows on rocky slopes. The varieties of cultivated onions are grouped as follows:
- Top, or Egyptian, Onions produce bulbils at the end of the seed stalk.
- Multiplier, or Potato, Onions produce bulbs that divide into several bulblets, each of which can produce a whole plant.
- Common Onions usually multiply by seeds. There are two main types of common onions. The strong-flavored American onions grow well in northern areas of the country and can be stored for a long time. The milder foreign varieties, such as the flat Bermuda onions and the large, sweet Spanish varieties, are raised in southern regions and do not keep well in storage. A few varieties are raised as green, or bunching, onions. Many disease-resistant and high-yielding hybrids have been developed from common onions.
Onions belong to the genus Allium of the lily family, Liliaceae. The common onion is A. cepa; the nodding onion, A. cernuum.