When to plant onion in Arizona
Arizona spans USDA zones 6a–10a, so the right time to plant onion shifts by weeks across the state. The window to transplant seedlings outdoors runs from about December 7 in Bullhead City to May 7 in Flagstaff — below are local dates for 68 cities, each computed from its own frost dates.
| City | Zone | Last frost | First frost | Transplant out |
|---|---|---|---|---|
| Phoenix | 9b | January 8 | December 25 | December 11 – December 25 |
| Tucson | 9b | February 5 | December 9 | January 8 – January 22 |
| Mesa | 9b | February 1 | December 10 | January 4 – January 18 |
| Gilbert | 9b | February 1 | December 11 | January 4 – January 18 |
| Chandler | 9b | February 13 | December 5 | January 16 – January 30 |
| Glendale | 9b | January 20 | December 15 | December 23 – January 6 |
| Scottsdale | 10a | January 27 | December 21 | December 30 – January 13 |
| Peoria | 9b | February 5 | December 11 | January 8 – January 22 |
Onion in Arizona: FAQ
When can I plant onion in Arizona?
Across Arizona, the time to transplant onion spans roughly December 7 in Bullhead City to May 7 in Flagstaff, each following that city's local frost dates.
Does the onion planting date vary across Arizona?
Yes. Arizona publishes 68 cities with their own frost dates, so the right onion planting window shifts by weeks between the warmest and coldest parts of the state — use your city's page for the exact dates.
How long does onion take to grow in Arizona?
Onion takes about 90–110 days to reach harvest once planted — check that this fits inside your city's frost-free season on its place page.
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