Onions
Allium cepa. ALLIACEAE.
Planting, Growing, and Harvesting Onions
You’ll find everything you need to know to plant and grow onion in the accompanying table’s tabs:
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- How many onions to plant
- Growing conditions for onions
- When to plant onions
- How to plant onions
- Watering, fertilizing, and lodging of onions
- Companion plantings for onion
- How to harvest, store, and use onion
Growing Onions
Onions are cool-season bulb vegetables. They have sturdy green foliage and swollen roots with papery tunicate layers covering their many concentric layers of crisp, juicy, distinctively pungent flesh. An onion-family—allium— vegetable.
Onions are phototropic, regulating their growth by the hours of sunlight they receive. Long-Day onion varieties grow best in mid- to high-latitude areas from 30°–50° north or south, while Short-Day onion varieties perform best in low- to mid-latitude areas from 15°–25° north or south. If unsure, choose Intermediate-Day or Day-Neutral onion varieties.
Onions and their close relatives—chives, garlic, leeks, and shallots—are very popular garden vegetables to sow from seed, set out as seedlings, or plant as sets—immature bulbs are available in autumn and spring. Harvest onions while young and green as scallions or when mature as brown, red, or white bulbs that easily dry and store well.
Ornamental Onion (Allium spp.) and Society Garlic (Tulbaghia violacea) are related ornamental bulbs frequently planted in landscapes and flower beds.
Onion Plant and Care Guide
How Much to Plant
Allow 20–30 plants per household member.
How to Plant
Seed germinates in 12-14 days.
Cold-Winter Climates: Sow seed indoors 4–6 weeks before soil warms to 35–90°F (2–32°C) and harden seedlings 5–7 days before transplanting.
Mild-Winter Climates: Set out seedlings or sets in full sun in late autumn.
Autumn–Winter Gardens:
Shallots and Overwintering Onions: Sow seed in early August or onion starts in early October for harvest in late spring–summer of the following season.
Bunching Onions: Sow seed from May–August or transplants from July–September for harvest in winter–spring.
Sow seed 1/2-in. (12-mm) deep, 1/2-in. (12-mm) apart, thinning to 4 in. (10 cm) apart, in rows 18–25 in. (45–63 cm) apart, or broadcast over an area and thin to 4 in. (10 cm) apart.
Best Conditions for Growth
45–85°F (7–29°C). Best in full sun. Shade plants from direct sun under very hot conditions.
Soil Type and Fertility
Moist, well-drained sandy soil. Fertility: Rich. 6–6.8 pH. Prepare soil at least 1 ft. (30 cm) deep. Rotate plantings with other vegetables to prevent accumulation of pest and disease organisms in soil.
Proper Care
Easy. Keep evenly moist. Apply ample water during the bulb-enlargement stage. Fertilize monthly during active growth with 5–10–10 formula. Mulch deeply to protect from frost. Cultivate.
Lodge foliage of bulb-forming varieties when seed heads form and flowers open; for bunching cultivars, trim off flowers and withered stalks [see: Lodging and Blanching]. Borer, thrip and nematode susceptible.
Pairing Recommendations
Beets, lettuce, summer savory, strawberries, and tomatoes.
Maturity, Picking and Gathering
80–150 days. Pull green onion bulbs while less than 1/2 in. (12 mm) wide; harvest bunching cultivars when bulbs are 1–2 in. (25–50 mm) wide, thinning from the outside of the bunch; pull drying onion bulbs when 3–5 in. (75–125 mm) wide and tops wither. Harvest promptly; leaving onions in ground causes mushy texture, bulb division.
How to Store and Preserve
Green and Bunching: Fresh in vegetable keeper of refrigerator for 2–3 weeks; chopped and frozen, 6–8 months. Drying: Cut 1–1⁄2 in. (38 mm) above the bulb or braid the stems into strands, cure 10–20 days in a shady, warm, dry spot, and store in a porous fabric bag in a cool, dry place, 4–6 months; chop, dry in a vegetable dehydrator, and seal in airtight plastic containers, 1 year; chop and freeze, 6–8 months.