Onion (transplants)
Vegetable · cool season · also called onion plants, onion bundles, bulb onion, onion from seed
When to plant
- Start seeds indoors about 10 weeks before planting out.
- Plant outdoors about 4 weeks before your average last spring frost.
- Ready to harvest about 100 days after planting out.
Buy bundles of plants, or start seed indoors. Pick the day-length type for your area. Harvest when tops fall over; cure 2 weeks.
Frost dates depend on where you live. Enter your ZIP code to get exact dates.
Dates by zone: 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a 9b 10a 10b
Growing basics
Harmful to pets. Every part is toxic to cats and dogs, raw or cooked. It damages their red blood cells.
- Sun
- Full sun (6+ hours)
- Spacing
- 4–6 in
- Soil temperature
- At least 45°F
- Time to harvest
- About 100 days
- Containers
- At least 2 gallons
- Plant family
- Onion family (alliums)
- Harvest per plant
- About 0.5 lb
- Seeds keep
- About 1 year
Companions
Keep apart: the bean and pea family (legumes). Onions and garlic can stunt beans and peas.
Keep apart: Asparagus. Onions and garlic can stunt asparagus.
Keep apart: Horseradish. Horseradish spreads aggressively. Give it its own spot.
Keep apart: Mint. Mint spreads aggressively into neighbors. Keep it in a pot.
Keep apart: Fennel (bulb). Fennel slows the growth of most garden plants. Grow it on its own.
Keep apart: Sunchoke (Jerusalem artichoke). Sunchokes spread aggressively and shade neighbors.
Grow it well
Tips
- Dry onions and garlic before storing them. Pull onions once most of their tops have flopped over, and garlic once the lower third of its leaves turn brown. Spread them somewhere airy and out of the sun for 2 to 3 weeks, until the necks are dry and papery.
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