Allium cepa (Onion)

A Staple in the kitchen, Onions (Allium cepa) are biennial vegetables grown for their sweet to pungent bulbs and greens. Native to Asia, Onions have been cultivated for 5000 years and provide fantastic flavor to any meal.

• Onions belong to the genus Allium and are closely related to garlic, shallots, and leeks.
• Onions are a versatile vegetable and a key ingredient in cuisines worldwide.
• Providing flavor, color, and texture to various dishes, Onions can be consumed dried or fresh, raw or cooked.
• Onions provide essential nutrients and have been valued for their medicinal qualities by many cultures worldwide, including the prevention of cancer and cardiovascular disorders.
• Onions are easy to grow from seed or from bulbs called sets.
• Onions are usually planted early in the spring and harvested from midsummer through the fall. They can also be planted in early fall if they get at least 4-6 weeks of warm temperatures to become established in the ground.
• Dormant during the cool season, they will spring to life in early spring when temperatures and soil are warm again.
• The size of Onion bulbs depends upon the number and size of the green leaves (tops) at the time of bulb maturity. Each leaf will have a ring of onion; the larger the leaf, the larger the ring will be.
• Onions are characterized by day length – the daylight hours required to grow bulbs.
• Long-Day Onion varieties will quit forming leaves and begin to form bulbs when the day length reaches 14-16 hours.
• Short-Day Onions will start making bulbs much earlier in the year when there are only 10-12 hours of daylight.

Main Types of Onion

Yellow Onions (Allium cepa var. cepa)

• Also known as Brown Onions, Yellow Onions are round, medium to large, 2-4 inches across (5-10 cm), with a light yellow to copper, dry, papery skin. The flesh is white to cream-colored, translucent, firm, crisp, and juicy.
• Crunchy with a pungent flavor when raw, they develop a nutty, mild flavor with sweet undertones when cooked.
• Highly popular, Yellow Onions account for over 80% of the United States Onion crop and are the most widely grown Onions in northern Europe.
• Yellow Onions store well and can be kept for 1-2 months when stored whole in a cool, dry, dark place with plenty of air circulation.
• Yellow Onions are a good source of vitamin C and fiber.
• Yellow Onions are the most common cooking Onions and are best suited for both raw and cooked dishes. They work well in various cuisines and can be dry-roasted, sauteed, grilled, caramelized, and braised. Famous for their use in the classic French Onion soup, Yellow Onions are often chopped and used as a flavoring for soups, stews, and stocks.

Red Onions (Allium cepa var. cepa)

• Also known as Purple Onions, Red Onions are round to slightly oval, medium to large, 4-6 inches across (10-15 cm), with a red-purple thin, papery skin. The flesh is dark purple, firm, and crisp, with many layers of white and purple rings.
• Crunchy with a pungent, sweet, and slightly spicy flavor when raw, they develop a mildly sweeter flavor when cooked.
• Red Onions can be found in North America, Central America, South America, Europe, Asia, and Australia.
• Red Onions store well and can be kept for 1-2 months when stored whole in a cool, dry, dark place with plenty of air circulation.
• Red Onions are a good source of vitamin C, fiber, iron, and calcium. They are rich in polyphenols and flavonoids, which provide antioxidant properties that contribute to overall health, and sulfur, which fights inflammation.
• Red Onions are best suited for both raw and cooked dishes. They can be grilled, roasted, braised, caramelized, and pickled. A favorite ingredient of sandwiches, burgers, wraps, gyros, and paninis, Red Onions can also be chopped and tossed into salads.

White Onions (Allium cepa var. cepa)

• White Onions are round, medium to large, with a bright white thin, papery skin. The flesh is white, almost translucent, firm, crisp, and juicy.
• Favored by chefs for their mild, semi-sweet, and sharp flavor, they are also often used as a finishing garnish in Mexican cuisine, especially for tacos and enchiladas. This onion is also great for raw sauces like salsa and guacamole.
• White Onions can be found in North America, Central America, South America, Europe, Asia, and Australia.
• White Onions store well and can be kept for 1-2 months when stored whole in a cool, dry, dark place with plenty of air circulation.
• White Onions contain vitamin C, fiber, potassium, calcium, and iron.
• White Onions can be used fresh in salads or layered on sandwiches, burgers, and wraps. They can be grilled, roasted, sauteed or fried, or chopped and added to soups and stews.

Sweet Onions (Allium cepa var. cepa)

• Aptly named, Sweet Onions are not pungent because they have a lower concentration of sulfur, which typically gives Onions their pungent taste.
• Crunchy, tender, mild, and sweet, they are perfect for using raw in salads and relishes. They are also great for caramelizing and served with roasted meats, on toast, or on pizza, fried into an onion ring, mixed into stews and soups, or grilled and served on burgers.
• Popular varieties include Vidalia onions, Walla Walla onions, Maui onions, Bermuda onions, Sweet Imperial, and Texas Spring Sweet.
• Sweet Onions do not store as well as other onions. They will keep for 1-2 weeks when stored in a paper bag in a cool and dark place.

Pearl Onions (Allium cepa var. cepa)

• Also known as Cocktail Onions, Picklers, Baby Onions, and Button Onions, Pearl Onions are small, pearl-shaped bulbs that can be white, yellow, or red.
• Crunchy and mild, they develop a sweet and slightly less pungent flavor than full-sized Onions when cooked. Pearl Onions are encouraged to remain small: they are planted in tight, dense rows and harvested when young.
• Pearl Onions can be bought fresh, pickled, or frozen.
• Pearl Onions store well and can be kept for 1-2 months when stored in a cool, dry, and dark place with good air circulation.
• Pearl Onions contain vitamin C, potassium, calcium, fiber, and flavonoids.
• Grown mostly for pickling as a cocktail Onion, Pearl Onions are famous for their use in creamed onion recipes, which were created in England and were also popular in Italian and French cuisine.

Shallots (Allium cepa var. aggregatum)

• Shallots look like slightly elongated onions covered with dry, papery, thin skin ranging from copper, gold, pale pink to red.
• Like garlic, Shallots are formed in clusters of cloves divided into individually wrapped segments. Small Shallot varieties include 2 to 3 cloves, and larger types typically contain 3 to 6 cloves.
• The flesh is firm, off-white to translucent, with light purple or red rings.
• Rich in spicy, sweet, and pungent flavors, Shallots are crisp and astringent when raw, but they develop a delicate, sweet taste with flavors reminiscent of garlic when cooked.
• Widely used in French cuisine for roasts, stews, and sauces, Shallots are also popular throughout Asia for their milder pungency.
• Shallots have been used for thousands of years in culinary and medicinal applications.
• Shallots are an excellent source of fiber, stimulating the digestive system, and a good source of the minerals iron, potassium, and magnesium. They also contain vitamins A and C, which are antioxidants that can help strengthen the immune system, and provide some calcium, zinc, vitamin E, selenium, and phosphorus.
• Shallots store well and can be kept for up to one month when stored in a cool, dry, and dark place.
• Shallots are best suited for raw and cooked uses such as roasting, sautéing, and grilling.

Onion Health Benefits

• While Onions are flavorful additions to salads and delicious dishes, they also provide some health benefits.
• Onions are low in calories but rich in nutrients, including vitamins and minerals.
• Onions contain a high level of vitamin C, which helps improve your immune system.
• Onions are also rich in vitamin B, including folate and vitamin B6, which play essential roles in metabolism, red blood cell production, and nerve function.
• Onions are a good source of potassium, which may boost your energy and metabolism. They also provide manganese, improving bone health and reducing blood clot risk.
• Onions are packed with antioxidants, including flavonoids, that can help fight free radicals, reduce cholesterol levels, lower heart disease risks, and may help protect against chronic conditions such as cancer and diabetes.
• One study shows that consuming a long-term diet high in flavonoids decreases the risk of getting Alzheimer’s disease.
• Onions also contain high levels of prebiotics and fiber, which help improve digestion, strengthen the immune system, and reduce inflammation.
• Onions have antibacterial properties that inhibit the growth of potentially harmful bacteria such as Escherichia coli, Pseudomonas aeruginosa, and Staphyloccus aureus.
• According to research, moderate consumption of Onions is associated with improved bone density.

Growing Onions

• Onions grow to 12-18 in. tall (30-45 cm) and 6-12 in. wide (15-30 cm).
• Onions perform best in full sun in fertile, moist but well-drained soils in a sheltered site. Ideal soil pH is between 6.0 and 7.0.
• Onions prefer cool temperatures early in their growth and warm temperatures near maturity. They grow best between 55-75°F (13-24°C)
• Onions will tolerate temperatures as low as 45°F (7°C) and as high as 85°F (29°C).
• Onions can be grown from set or from seed. Sets are tiny bulbs that were grown from seed the previous year.
• Sets are easier and quicker to grow and less likely to be affected by diseases, but seed-grown plants can be less susceptible to bolting (flowering). To reduce the risk of bolting, choose heat-treated sets.
• Depending on the variety, Onions take 90-100 days to harvest from seed and 80 days to harvest from sets.
• Sets can be planted directly in the garden about 2 weeks before the last frost.
• In cooler climates, seeds must be started indoors at least 8 to 10 weeks before the last frost.
• Onions are best grown on raised beds at least 4 in. high (10 cm) and 20 in. wide (50 cm).
• Onion plants are heavy feeders: dig in a generous amount of garden compost or well-rotted manure before planting to add nutrients and improve the soil texture.
• Onion growth and yield can also be significantly enhanced by adding a fertilizer rich in phosphorous (10-20-10) at planting time.
• Sow seeds ½ in. deep (1.3 cm) in rows 8 in. apart (20 cm). Thin out seedlings first to 2 in. apart (5 cm) apart and later to 4 in. apart (10cm).
• Plant the sets ¾ in. deep (2cm) in drills or gently push them into loose soil, so the tip is just showing at the surface. Space them 2–4 in. apart (5–10 cm) in rows 10–12 in. apart (25–30cm).
• Closer planting will result in a larger Onion crop but smaller individual bulbs.
• Onions are shallow-rooted and require constant moisture for proper growth.
• Keep the soil moist but not soggy because Onions are susceptible to root rot diseases.
• Add nitrogen-based fertilizer about 3 weeks after planting and then continue with applications every 2 to 3 weeks.
• Mulch with composted leaves or straw to maintain soil organic content, retain moisture, prevent disease, and control weeds.
• Cut off any flower stems that emerge in spring, as they may decrease the size of your Onion bulbs.
• Stop watering and feeding once the Onions have swollen in mid-summer.
• Onions are ready to be harvested when their tops flop over and gradually dry and turn yellow.
• Fall-planted sets are ready to harvest by early to mid-summer, while spring-sown or spring-planted Onions are ready in late summer to early fall.
• Once Onions have flopped, lay them in the sun to let them cure. When completely dried, brush the dust carefully without disturbing the Onion skin. Onions can be braided or stored in mesh bags.
• Practice crop rotation: avoid planting Onions where onion family members have been grown during the previous 3 years.
• Onions are susceptible to various pests. Keep an eye out for birds, onion fly, onion root maggot, aphids, thrips, slugs, and snails.
• Onions are susceptible to various diseases, including onion white rot, onion pink root, leek rust, and downy mildew.
• Onions are deer and rabbit resistant.
• Propagate by seed or by planting out sets in spring or fall.
• Toxic to dogs, toxic to cats, toxic to horses.

Onion: Companion Planting

• Onions are one of the best companion plants in the garden. Their smell protects against pests, and their compact size allows them to be interplanted wherever there is room.
• Excellent companion plants for Onions are apples, apricots, beet, broccoli, cabbage, carrots, chamomile, cherries, chili peppers, kohlrabi, leeks, lettuce, lovage, marigold, marjoram, parsley, parsnip, peaches, peppers, potatoes, radish, rosemary, rue, rutabaga, spinach, strawberry, squash, summer savory, swiss chard, and tomatoes.
• Onions planted near carrots help repel the carrot fly.
• Onions discourage rabbits from eating your cabbage and lettuce plants.
• Planting Onions and carrots together will boost the productivity of your vegetable bed because they feed at two different soil levels. While the onion roots stay just under the surface of the ground to get their nutrients, carrots push their roots very deep.
• Chamomile and Summer Savory can improve the vigor and flavor of your Onions.
• Rue is known to deter aphids, onion maggots, slugs, snails, fish moths, and fleas.
• Leeks will improve the growth of your Onions.
• Use the strong scent of onions to keep pests away from fruit trees (apple, apricot, cherry, peach) and strawberries.
• Onion is believed to deter the Colorado potato beetle.
• Do not plant Onions near asparagus, beans, sage, or peas.