onion

Onion (Allium cepa) is a vegetable cultivated for its large edible bulb and, in some forms, its slender, edible leaves. It belongs to the genus Allium in the Amaryllidaceae family. The name derives from Latin cepa, meaning onion. Onions are grown worldwide and appear in many culinary traditions.

Most commonly grown varieties are categorized by color: yellow, red, and white onions. Sweet onions, such as Vidalia and Walla Walla, have milder flavor and lower sulfur content. A closely related harvest is the scallion or green onion, which is picked for its immature greens rather than a developed bulb.

Onion bulbs form as the plant’s leaves swell underground. They thrive in fertile, well-drained soil and cool to moderate climates. Long-day onions perform best in higher latitudes, while short-day varieties suit warmer regions. Plants are often started as sets or transplants and grown with regular irrigation. Harvest occurs when the tops dry and fall over; bulbs are cured to improve storage life. Properly cured onions store in a cool, dry, ventilated environment for several months.

Culinary uses are diverse: onions are used raw in salads and salsas or cooked in soups, stews, sautés, and caramelized dishes. Flavor arises from sulfur-containing compounds released when the tissue is cut or damaged; enzymes produce compounds such as allicin. Nutritionally, onions are low in calories and provide vitamin C, several B vitamins, fiber, and various antioxidants.

Safety and cultivation notes: raw onions can irritate the eyes when cut, and some individuals have allergies or intolerance. Common pests include onion maggots and thrips; diseases such as downy mildew and basal rot can affect crops.