When to Plant Onions in Arizona
In Arizona, the time to plant onions outside runs from Dec 7 – Dec 21 in Bullhead City to May 7 – May 21 in Flagstaff. In Phoenix, it's Dec 11 – Dec 25. The average last spring frost differs by about 22 weeks across the state (Jan 4 in Bullhead City, Jun 4 in Flagstaff), so use the dates for the town nearest you.
Onions are cold-hardy. Plant sets or transplants early so they grow leaves before long summer days trigger bulbing.
- Start indoors: 10–12 weeks before the last frost.
- Plant outside: 2–4 weeks before the last frost.
Onions planting dates in Arizona by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Apache Junction | 9b | Nov 19 – Dec 3 | Jan 14 – Jan 28 |
| Avondale | 9b | Oct 22 – Nov 5 | Dec 17 – Dec 31 |
| Buckeye | 9b | Oct 15 – Oct 29 | Dec 10 – Dec 24 |
| Bullhead City | 10a | Oct 12 – Oct 26 | Dec 7 – Dec 21 |
| Camp Verde | 8b | Jan 22 – Feb 5 | Mar 19 – Apr 2 |
| Casa Grande | 9a | Nov 13 – Nov 27 | Jan 8 – Jan 22 |
| Chandler | 9b | Nov 21 – Dec 5 | Jan 16 – Jan 30 |
| Chino Valley | 8a | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
| Coolidge | 9a | Nov 25 – Dec 9 | Jan 20 – Feb 3 |
| Cottonwood | 8b | Jan 5 – Jan 19 | Mar 2 – Mar 16 |
| Douglas | 8a | Dec 24 – Jan 7 | Feb 18 – Mar 4 |
| El Mirage | 9b | Oct 28 – Nov 11 | Dec 23 – Jan 6 |
| Eloy | 9a | Dec 2 – Dec 16 | Jan 27 – Feb 10 |
| Flagstaff | 6a | Mar 12 – Mar 26 | May 7 – May 21 |
| Florence | 9a | Nov 7 – Nov 21 | Jan 2 – Jan 16 |
| Fountain Hills | 9b | Oct 14 – Oct 28 | Dec 9 – Dec 23 |
| Gilbert | 9b | Nov 9 – Nov 23 | Jan 4 – Jan 18 |
| Glendale | 9b | Oct 28 – Nov 11 | Dec 23 – Jan 6 |
| Goodyear | 9b | Oct 22 – Nov 5 | Dec 17 – Dec 31 |
| Kingman | 9a | Jan 8 – Jan 22 | Mar 5 – Mar 19 |
| Lake Havasu City | 10a | Oct 13 – Oct 27 | Dec 8 – Dec 22 |
| Marana | 9b | Jan 8 – Jan 22 | Mar 5 – Mar 19 |
| Maricopa | 9a | Dec 1 – Dec 15 | Jan 26 – Feb 9 |
| Mesa | 9b | Nov 9 – Nov 23 | Jan 4 – Jan 18 |
| Nogales | 8b | Dec 26 – Jan 9 | Feb 20 – Mar 6 |
| Oro Valley | 9a | Jan 8 – Jan 22 | Mar 5 – Mar 19 |
| Paradise Valley | 10a | Oct 14 – Oct 28 | Dec 9 – Dec 23 |
| Payson | 8b | Feb 4 – Feb 18 | Apr 1 – Apr 15 |
| Peoria | 9b | Nov 13 – Nov 27 | Jan 8 – Jan 22 |
| Phoenix | 9b | Oct 16 – Oct 30 | Dec 11 – Dec 25 |
| Prescott | 7b | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Prescott Valley | 7b | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Queen Creek | 9b | Nov 9 – Nov 23 | Jan 4 – Jan 18 |
| Sahuarita | 9a | Dec 3 – Dec 17 | Jan 28 – Feb 11 |
| Scottsdale | 10a | Nov 4 – Nov 18 | Dec 30 – Jan 13 |
| Show Low | 7a | Feb 10 – Feb 24 | Apr 7 – Apr 21 |
| Sierra Vista | 8b | Jan 11 – Jan 25 | Mar 8 – Mar 22 |
| Surprise | 9b | Nov 13 – Nov 27 | Jan 8 – Jan 22 |
| Tempe | 10a | Nov 21 – Dec 5 | Jan 16 – Jan 30 |
| Tucson | 9b | Nov 13 – Nov 27 | Jan 8 – Jan 22 |
Calculated from each town's average (50%) frost dates, from the nearest NOAA station (1991–2020). Typical dates for the 2027 planting season, based on NOAA's 1991–2020 averages. They are long-term odds, not a forecast: always check your local forecast before planting. Zones: 2023 USDA Plant Hardiness Zone Map (USDA-ARS and Oregon State University). Not the official map; see planthardiness.ars.usda.gov.
Parts of Arizona rarely see frost (for example Yuma, San Luis, Somerton). There, planting is timed by heat rather than frost, usually in the cooler months; look up your ZIP code for details.
See all frost dates in Arizona, or the general guide to when to plant onions.
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