Last spring frost
Feb 26
Frost Dates for Diablo Grande, CA
First fall frost
Nov 29
Growing season
273 days
Hardiness zone
9b
In an average year around Diablo Grande, CA, the last spring frost (32°F) is about Feb 26 and the first fall frost is about Nov 29, giving roughly a 273-day growing season. To be safe most years, wait until Jan 18 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 6 | Apr 7 | Mar 3 |
| Freeze (32°F) | Apr 21 | Feb 26 | Jan 18 |
| Hard (28°F) | Mar 31 | Jan 20 | Dec 21 |
| Severe (24°F) | Mar 2 | Jan 4 | Dec 16 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 6 | Apr 28 | Apr 21 | Apr 14 | Apr 7 | Mar 31 | Mar 24 | Mar 14 | Mar 3 |
| 32°F | Apr 21 | Apr 9 | Mar 26 | Mar 7 | Feb 26 | Feb 16 | Feb 7 | Jan 31 | Jan 18 |
| 28°F | Mar 31 | Feb 18 | Feb 1 | Jan 27 | Jan 20 | Jan 12 | Jan 5 | Dec 30 | Dec 21 |
| 24°F | Mar 2 | Jan 20 | Jan 13 | Jan 7 | Jan 4 | Dec 31 | Dec 28 | Dec 24 | Dec 16 |
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) | Oct 26 | Nov 14 | Dec 1 |
| Freeze (32°F) | Nov 12 | Nov 29 | Dec 21 |
| Hard (28°F) | Nov 24 | Dec 12 | Jan 16 |
| Severe (24°F) | Dec 7 | Dec 27 | Jan 19 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 26 | Nov 1 | Nov 6 | Nov 10 | Nov 14 | Nov 17 | Nov 20 | Nov 24 | Dec 1 |
| 32°F | Nov 12 | Nov 17 | Nov 21 | Nov 25 | Nov 29 | Dec 2 | Dec 5 | Dec 10 | Dec 21 |
| 28°F | Nov 24 | Dec 1 | Dec 4 | Dec 8 | Dec 12 | Dec 18 | Dec 26 | Jan 2 | Jan 16 |
| 24°F | Dec 7 | Dec 12 | Dec 18 | Dec 22 | Dec 27 | Dec 31 | Jan 3 | Jan 8 | Jan 19 |
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: Newman, Ca, about 14.3 miles away@if(!empty($station['elevation_ft'])), at 90 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 Diablo Grande, CA?
On average, the last spring frost (32°F) around Diablo Grande, CA is about Feb 26. In cooler years it can run later, so for a safer bet many gardeners wait until Jan 18.
When is the first frost in the fall?
The first fall frost around Diablo Grande, CA typically arrives about Nov 29. 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 Feb 26 on average, or Jan 18 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 273 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 95363 Planting calendar → California frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026