When to plant onion by zone
Allium cepa is a cool-season crop that is hardy to frost. Rule of thumb: start seeds indoors 10–12 weeks before the last frost; plant out from 4 weeks before to 2 weeks before the last frost.
Onion planting dates by zone
Each row uses the median 30%-risk frost dates of the major cities in that zone; rows marked * have no major city and use the median of NOAA stations in that zone instead. Frost dates vary a lot within a zone, so use your city page for local dates. In frost-free climates: Oct 15 – Jan 15.
| Zone | Median last frost | Start indoors | Transplant / plant out | Direct sow | Fall crop |
|---|---|---|---|---|---|
| 1a* | May 29 | Mar 6 – Mar 20 | May 1 – May 15 | — | — |
| 1b* | May 29 | Mar 6 – Mar 20 | May 1 – May 15 | — | — |
| 2a | May 21 | Feb 26 – Mar 12 | Apr 23 – May 7 | — | — |
| 2b* | May 20 | Feb 25 – Mar 11 | Apr 22 – May 6 | — | — |
| 3a* | Jun 4 | Mar 12 – Mar 26 | May 7 – May 21 | — | — |
| 3b* | May 24 | Mar 1 – Mar 15 | Apr 26 – May 10 | — | — |
| 4a | May 12 | Feb 17 – Mar 3 | Apr 14 – Apr 28 | — | — |
| 4b | May 5 | Feb 10 – Feb 24 | Apr 7 – Apr 21 | — | — |
| 5a | May 4 | Feb 9 – Feb 23 | Apr 6 – Apr 20 | — | — |
| 5b | May 4 | Feb 9 – Feb 23 | Apr 6 – Apr 20 | — | — |
| 6a | May 4 | Feb 9 – Feb 23 | Apr 6 – Apr 20 | — | — |
| 6b | Apr 26 | Feb 1 – Feb 15 | Mar 29 – Apr 12 | — | — |
| 7a | Apr 22 | Jan 28 – Feb 11 | Mar 25 – Apr 8 | — | — |
| 7b | Apr 10 | Jan 16 – Jan 30 | Mar 13 – Mar 27 | — | — |
| 8a | Apr 1 | Jan 7 – Jan 21 | Mar 4 – Mar 18 | — | — |
| 8b | Mar 22 | Dec 28 – Jan 11 | Feb 22 – Mar 8 | — | — |
| 9a | Mar 11 | Dec 17 – Dec 31 | Feb 11 – Feb 25 | — | — |
| 9b | Feb 12 | Nov 20 – Dec 4 | Jan 15 – Jan 29 | — | — |
| 10a | Jan 26 | Nov 3 – Nov 17 | Dec 29 – Jan 12 | — | — |
| 10b | Jan 27 | Nov 4 – Nov 18 | Dec 30 – Jan 13 | — | — |
| 11a | Rare | Oct 15 – Jan 15 | |||
| 11b* | Rare | Oct 15 – Jan 15 | |||
| 12a* | Rare | Oct 15 – Jan 15 | |||
| 12b | Rare | Oct 15 – Jan 15 | |||
| 13a* | Rare | Oct 15 – Jan 15 | |||
| 13b* | Rare | Oct 15 – Jan 15 | |||
Growing tips
- Match the type to your latitude: long-day onions in the North, short-day in the South.
- Onions bulb in response to day length, so an early start gives bigger bulbs.
- In frost-rare climates, plant short-day onions in fall for a spring harvest.
Related guides: which frost date to use · succession and fall planting.
Exact dates for your city
Popular: New York, Los Angeles, Chicago, Houston, Phoenix, Philadelphia, San Antonio, San Diego, Dallas, Jacksonville, Fort Worth, San Jose — or browse all cities by state.
Other crops: Tomato, Pepper, Lettuce, Green Beans, Sweet Corn, Zucchini & Summer Squash, Cucumber, Carrot, Potato, Basil, Spinach, Kale, Broccoli, Peas, Eggplant, Cabbage, Radish, Strawberry, Beets
Onion planting questions
When should I start onion seeds indoors?
About 10–12 weeks before your last spring frost. Using the median frost dates of cities on this site: zone 5a (median last frost May 4): Feb 9 – Feb 23; zone 6b (median last frost Apr 26): Feb 1 – Feb 15; zone 8a (median last frost Apr 1): Jan 7 – Jan 21.
When can I plant onion outside?
Set out transplants from 4 weeks before to 2 weeks before the last frost, once the soil reaches about 50°F (10.0°C). Examples: zone 5a (median last frost May 4): Apr 6 – Apr 20; zone 6b (median last frost Apr 26): Mar 29 – Apr 12; zone 8a (median last frost Apr 1): Mar 4 – Mar 18.
How long does onion take to grow?
90–120 days from transplant. As a hardy cool-season crop it grows best in cool weather, so spring plantings should mature before summer heat, and fall plantings need about two extra weeks because days are shorter.
What soil temperature does onion need?
At least 50°F (10.0°C) at planting depth. Cold soil slows root growth more than a short delay in planting does, so in a cold spring it pays to wait a week past the usual date. As a hardy crop, onion tolerates light frost.
How far apart should I plant onion?
Recommended in-row spacing: 4–6 in. Match the type to your latitude: long-day onions in the North, short-day in the South.
When do you plant onion where frost is rare?
In frost-free climates, plant onion Oct 15 – Jan 15, timing growth for the mildest months. This applies to cities such as Los Angeles, CA, San Diego, CA, San Francisco, CA.