- Hardiness
- Grown as a yearly crop in every zone
- Light
- Full sun
- Water
- Average, about an inch a week
- Size
- 1 to 2 ft
- Days to harvest
- 90 to 120
- Start indoors
- 10 weeks before planting out
Growing tip. Pick the right day length: short-day onions for the South, long-day for the North. Plant sets or plants early in spring.
When to plant onion by zone
| Zone | Median last / first frost | When to plant |
|---|---|---|
| 3b | May 16 / Sep 25 | Plant outside: Apr 4 to Apr 18 Start seeds indoors: around Jan 24 |
| 4a | May 12 / Sep 28 | Plant outside: Mar 31 to Apr 14 Start seeds indoors: around Jan 20 |
| 4b | May 8 / Oct 1 | Plant outside: Mar 27 to Apr 10 Start seeds indoors: around Jan 16 |
| 5a | May 3 / Oct 5 | Plant outside: Mar 22 to Apr 5 Start seeds indoors: around Jan 11 |
| 5b | May 1 / Oct 10 | Plant outside: Mar 20 to Apr 3 Start seeds indoors: around Jan 9 |
| 6a | Apr 29 / Oct 16 | Plant outside: Mar 18 to Apr 1 Start seeds indoors: around Jan 7 |
| 6b | Apr 22 / Oct 22 | Plant outside: Mar 11 to Mar 25 Start seeds indoors: around Jan 1 |
| 7a | Apr 16 / Oct 25 | Plant outside: Mar 5 to Mar 19 Start seeds indoors: around Jan 1 |
| 7b | Apr 5 / Nov 1 | Plant outside: Feb 22 to Mar 8 Start seeds indoors: around Jan 1 |
| 8a | Mar 29 / Nov 7 | Plant outside: Feb 15 to Mar 1 Start seeds indoors: around Jan 1 |
| 8b | Mar 16 / Nov 14 | Plant outside: Feb 2 to Feb 16 Start seeds indoors: around Jan 1 |
| 9a | Mar 2 / Nov 26 | Plant outside: Jan 19 to Feb 2 Start seeds indoors: around Jan 1 |
| 9b | Feb 1 / Dec 9 | Plant outside: Jan 1 to Jan 4 Start seeds indoors: around Jan 1 |
Zones 10 and warmer have little or no frost. There, plant cool-season plants in fall and warm-season plants from late winter.
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Frequently asked questions
What zone does onion grow in?
Onion is grown fresh each year, so it fits every zone. What changes is when you plant. Find your zone by ZIP code.
How much sun does onion need?
Full sun. Full sun means at least six hours of direct sun a day; part shade means about three to six.
Hardiness ranges, light and size are typical figures from university extension services and botanic garden plant records; a named variety can differ, so check its tag. Planting dates come from each zone's median frost dates (NOAA 1991 to 2020 climate normals) and the timing rules in how we check.