Onion
Allium cepa
Family: Amaryllidaceae
Onion grows in full sun and prefers loose, fertile, well-drained soil. Water needs: Moderate; keep soil evenly moist during active growth.
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How to Grow Onion
Onion growing information includes sunlight requirements of Full sun, soil conditions listed as Loose, fertile, well-drained soil with a soil pH of 6.0-7.0, and Moderate; keep soil evenly moist during active growth water needs. The listed hardiness zones are 3-9 depending on cultivar and season. For propagation reference, the database lists germination or establishment information for Onion as 7-14 days, with planting or establishment depth listed as 1/4 inch. Days to maturity are listed as 90-120 days from seed depending on cultivar.
Plant Overview
Onion (Allium cepa) is listed in the Amaryllidaceae family and categorized as a vegetable with a biennial commonly grown as an annual life cycle. This profile summarizes growing information for hardiness, light, soil, water, seed starting, maturity, and other available cultivation details. Difficulty is listed as Moderate.
- Plant ID
- PLT-0025
- Family
- Amaryllidaceae
- Plant type
- Vegetable
- Life cycle
- Biennial commonly grown as an annual
- Alternate names
- Bulb onion; common onion
- Growth habit
- Upright bulb-forming herb with hollow leaves
- Mature height
- Approximately 12-24 inches
- Mature spread
- Approximately 4-8 inches
- Difficulty
- Moderate
Growing Conditions
Onion is listed for full sun conditions. Water needs are listed as moderate; keep soil evenly moist during active growth. The database soil reference is Loose, fertile, well-drained soil. The listed soil pH range is 6.0-7.0, and the listed hardiness range is 3-9 depending on cultivar and season.
- Hardiness zones
- 3-9 depending on cultivar and season
- Sunlight
- Full sun
- Soil
- Loose, fertile, well-drained soil
- Soil pH
- 6.0-7.0
- Water needs
- Moderate; keep soil evenly moist during active growth
- Plant spacing
- 3-6 inches for bulb onions
Seed & Germination
For seed starting, the listed germination time is 7-14 days and the seed depth is 1/4 inch. The listed time to maturity is 90-120 days from seed depending on cultivar. Use these values as general reference points and adjust for local climate, seed source, and growing conditions.
- Germination
- 7-14 days
- Germination temperature
- About 50-85°F; best near 65-75°F
- Seed depth
- 1/4 inch
- Sowing method
- Direct sow or start indoors for transplanting
- Start indoors
- Often started 8-10 weeks before transplanting outdoors
- Transplanting
- Transplant seedlings while young, spacing according to desired bulb size
Harvest & Propagation
- Days to maturity
- 90-120 days from seed depending on cultivar
- Harvest
- Harvest when tops yellow and fall over; cure bulbs in a dry, ventilated place before storage
- Propagation
- Primarily by seed or sets
- Pollination
- Insect-pollinated when allowed to flower
Garden Information
- Common pests
- Onion thrips, onion maggots and cutworms
- Common diseases
- Downy mildew, botrytis neck rot, basal rot and purple blotch
- Uses
- Fresh eating, cooking, grilling, pickling, soups and storage
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Growing Reference Note
Plant performance can vary with climate, soil, weather, cultivar, seed quality, and gardening methods. The values on this page are general database reference ranges rather than a substitute for local extension guidance or seed-packet instructions.