GreenlyFrost dates and when to plant in Arizona
United States
In Arizona the last spring frost comes between 4 February (Phoenix) and 5 May (Flagstaff) — the median of 2016–2025 in 3 cities. The first autumn frost comes between 21 October (Flagstaff) and 29 December (Phoenix). The frost-free season lasts 169–328 days. One of the 4 cities had no frost at all. Tomato: plant out into open ground 11 February – 8 September, earliest in Phoenix, latest in Phoenix.
Frost dates by city in Arizona
| City | Last spring frost | First autumn frost | Frost-free days | Climate zone | Tomato: window |
|---|---|---|---|---|---|
| Phoenix | 4 February | 29 December | 328 | 270 frost-free days or more | 11 February – 8 September |
| Tucson | 6 February | 18 December | 315 | 270 frost-free days or more | 14 February – 28 August |
| Flagstaff | 5 May | 21 October | 169 | 150–209 frost-free days | 12 May – 1 July |
| Yuma | none in ten years | none in ten years | — | No frost in ten years | — |
Median of 2016–2025 for the 25 km grid cell of the city: the last day at or below 0 °C in spring and the first in autumn (ERA5 reanalysis via Open-Meteo). In a cold year a frost can come a week or two later — Greenly warns 48 hours ahead.
When to plant in Arizona: windows by crop
The earliest start and the latest end among the cities here, each with its city; every city’s own window is on its page. Each window starts on the Greenly calendar date and ends on the last day that still leaves the crop’s days to harvest (from its card) before the average first autumn frost, plus six weeks of picking for crops harvested over weeks (tomatoes, peppers, aubergines, cucumbers, courgettes, pumpkins, watermelons, beans) — our rule; earlier in the window is safer.
| Crop | Planting out or sowing |
|---|---|
| Tomato | 11 February (Phoenix) – 8 September (Phoenix) |
| Cucumber | 23 February (Phoenix) – 14 October (Phoenix) |
| Bell Pepper, Eggplant | 23 February (Phoenix) – 8 September (Phoenix) |
| Zucchini | 23 February (Phoenix) – 12 October (Phoenix) |
| Pumpkin | 23 February (Phoenix) – 3 September (Phoenix) |
| Watermelon | 23 February (Phoenix) – 19 September (Phoenix) |
| Peas | 14 January (Phoenix) – 16 October (Phoenix) |
| Garlic, Tulip, Daffodil, Crocus, Hyacinth | Autumn planting: by 29 November (Phoenix) |
Weather by month in Arizona
Across the 4 cities the warmest month is July (average days 29.7 … 43 °C) and the coldest January (average nights -5 … 8.2 °C). 1 of the 4 cities have months with nights below 0 °C on average; the longest such winter is in Flagstaff (December–March).
| Month | Day, °C | Night, °C | Rain, mm |
|---|---|---|---|
| January | 4.8 … 21 °C | -5 … 8.2 °C | 35 |
| February | 7.6 … 24 °C | -3.7 … 9.7 °C | 31 |
| March | 10.9 … 27.2 °C | -1.3 … 12.3 °C | 27 |
| April | 17.4 … 32.4 °C | 3 … 16 °C | 5 |
| May | 21.4 … 35.4 °C | 7 … 20 °C | 3 |
| June | 28.4 … 40.9 °C | 13.7 … 25.9 °C | 8 |
| July | 29.7 … 43 °C | 16.5 … 29.2 °C | 52 |
| August | 27.8 … 42.4 °C | 15.3 … 28.5 °C | 40 |
| September | 24.7 … 39.1 °C | 12.1 … 24.9 °C | 28 |
| October | 18.4 … 33.6 °C | 6 … 18.3 °C | 26 |
| November | 11.8 … 26.4 °C | 0.7 … 12.7 °C | 23 |
| December | 7.2 … 21.4 °C | -2.5 … 8.8 °C | 30 |
Day and night: the lowest … highest monthly average among the cities; rain: the middle city (ERA5 via Open-Meteo).
What to plant month by month: the Southwest
Other regions: United States
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More about the United States
- Gardening in the United States: climate zones and crops by region
- United States: frost dates by city
- When to plant tomatoes in the United States
- When to plant cucumbers in the United States
- When to plant bell peppers in the United States
- When to plant peas in the United States
- When to plant garlic in the United States
- Gardening by country
