Last spring frost
May 24
Frost Dates for Williamson, AZ
First fall frost
Oct 7
Growing season
135 days
Hardiness zone
7b
In an average year around Williamson, AZ, the last spring frost (32°F) is about May 24 and the first fall frost is about Oct 7, giving roughly a 135-day growing season. To be safe most years, wait until May 7 before setting out tender plants.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Jun 26 | Jun 8 | May 24 |
| Freeze (32°F) | Jun 11 | May 24 | May 7 |
| Hard (28°F) | May 27 | May 6 | Apr 18 |
| Severe (24°F) | May 9 | Apr 17 | Mar 30 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 26 | Jun 19 | Jun 14 | Jun 11 | Jun 8 | Jun 5 | Jun 2 | May 30 | May 24 |
| 32°F | Jun 11 | Jun 5 | Jun 1 | May 29 | May 24 | May 20 | May 17 | May 13 | May 7 |
| 28°F | May 27 | May 19 | May 15 | May 11 | May 6 | May 3 | Apr 30 | Apr 25 | Apr 18 |
| 24°F | May 9 | May 3 | Apr 28 | Apr 23 | Apr 17 | Apr 13 | Apr 8 | Apr 4 | Mar 30 |
| 20°F | Apr 24 | Apr 14 | Apr 7 | Apr 2 | Mar 29 | Mar 23 | Mar 18 | Mar 13 | Mar 4 |
| 16°F | Apr 2 | Mar 20 | Mar 11 | Mar 6 | Mar 1 | Feb 25 | Feb 18 | Feb 10 | Jan 31 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Sep 16 | Sep 29 | Oct 10 |
| Freeze (32°F) | Sep 27 | Oct 7 | Oct 23 |
| Hard (28°F) | Oct 4 | Oct 18 | Nov 4 |
| Severe (24°F) | Oct 13 | Oct 31 | Nov 14 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 16 | Sep 20 | Sep 24 | Sep 26 | Sep 29 | Oct 1 | Oct 2 | Oct 5 | Oct 10 |
| 32°F | Sep 27 | Oct 1 | Oct 2 | Oct 5 | Oct 7 | Oct 10 | Oct 13 | Oct 17 | Oct 23 |
| 28°F | Oct 4 | Oct 8 | Oct 11 | Oct 15 | Oct 18 | Oct 22 | Oct 26 | Oct 31 | Nov 4 |
| 24°F | Oct 13 | Oct 19 | Oct 24 | Oct 28 | Oct 31 | Nov 3 | Nov 5 | Nov 9 | Nov 14 |
| 20°F | Oct 24 | Oct 31 | Nov 4 | Nov 7 | Nov 11 | Nov 14 | Nov 18 | Nov 21 | Nov 27 |
| 16°F | Nov 5 | Nov 11 | Nov 16 | Nov 20 | Nov 23 | Nov 27 | Dec 1 | Dec 3 | Dec 10 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Walnut Creek, Az, about 11.3 miles away@if(!empty($station['elevation_ft'])), at 5,090 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
When is the last frost in Williamson, AZ?
On average, the last spring frost (32°F) around Williamson, AZ is about May 24. In cooler years it can run later, so for a safer bet many gardeners wait until May 7.
When is the first frost in the fall?
The first fall frost around Williamson, AZ typically arrives about Oct 7. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around May 24 on average, or May 7 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 135 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 86305 Planting calendar → Arizona frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026