Onion (Allium cepa) is a biennial bulb grown as an annual in the Amaryllidaceae (allium) family. It is cultivated for its underground bulb, which is one of the most widely used flavoring ingredients in cooking. Onions are native to Central Asia.
Onions have been cultivated for at least 5,000 years. They appear in ancient Egyptian tomb paintings and were consumed by the builders of the pyramids. Onions were used in ancient Greece and Rome for both culinary and medicinal purposes. The plant spread along trade routes throughout the world.
Onions are used as a base ingredient in cuisines worldwide. They are consumed raw, cooked, pickled, and dehydrated. Onions contain organosulfur compounds that have documented antimicrobial and cardiovascular health benefits.
Onions are harvested when the tops have fallen over and the neck is drying. The bulbs are cured in a well-ventilated area out of direct sunlight for 2 to 3 weeks. Cured onions are stored in a cool, dry, well-ventilated location for 4 to 8 months, depending on the variety.
Onion bulb formation is triggered by day length. Short-day varieties are grown in southern regions, while long-day varieties are suited to northern latitudes. Onions require consistent moisture and fertile soil. Weed control is critical, as onions are poor competitors.