Last spring frost
Mar 8
Frost Dates for Clayton, CA
First fall frost
Dec 22
Growing season
282 days
Hardiness zone
9b
In an average year around Clayton, CA, the last spring frost (32°F) is about Mar 8 and the first fall frost is about Dec 22, giving roughly a 282-day growing season. To be safe most years, wait until Jan 12 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) | May 20 | Apr 19 | Mar 16 |
| Freeze (32°F) | Apr 15 | Mar 8 | Jan 12 |
| Hard (28°F) | Mar 23 | Feb 8 | Dec 21 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 20 | May 10 | May 1 | Apr 25 | Apr 19 | Apr 13 | Apr 7 | Mar 30 | Mar 16 |
| 32°F | Apr 15 | Apr 5 | Mar 28 | Mar 19 | Mar 8 | Feb 27 | Feb 18 | Jan 31 | Jan 12 |
| 28°F | Mar 23 | Mar 3 | Feb 26 | Feb 19 | Feb 8 | Jan 30 | Jan 14 | Jan 4 | Dec 21 |
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) | Nov 6 | Nov 29 | Dec 20 |
| Freeze (32°F) | Nov 23 | Dec 22 | Feb 11 |
| Hard (28°F) | Dec 8 | Jan 16 | Mar 3 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 6 | Nov 14 | Nov 19 | Nov 25 | Nov 29 | Dec 2 | Dec 6 | Dec 12 | Dec 20 |
| 32°F | Nov 23 | Dec 1 | Dec 9 | Dec 15 | Dec 22 | Jan 1 | Jan 8 | Jan 22 | Feb 11 |
| 28°F | Dec 8 | Dec 20 | Dec 30 | Jan 4 | Jan 16 | Jan 29 | Feb 10 | Feb 22 | Mar 3 |
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: Mt Diablo Junction, Ca, about 2.2 miles away@if(!empty($station['elevation_ft'])), at 2,170 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 Clayton, CA?
On average, the last spring frost (32°F) around Clayton, CA is about Mar 8. In cooler years it can run later, so for a safer bet many gardeners wait until Jan 12.
When is the first frost in the fall?
The first fall frost around Clayton, CA typically arrives about Dec 22. 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 Mar 8 on average, or Jan 12 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 282 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 94517 Planting calendar → California frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026