Last spring frost
Jan 16
Frost Dates for California Polytechnic State University, CA
First fall frost
Dec 25
Growing season
349 days
Hardiness zone
9b
In an average year around California Polytechnic State University, CA, the last spring frost (32°F) is about Jan 16 and the first fall frost is about Dec 25, giving roughly a 349-day growing season. To be safe most years, wait until Dec 11 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) | Apr 12 | Feb 28 | Jan 9 |
| Freeze (32°F) | Feb 26 | Jan 16 | Dec 11 |
| Hard (28°F) | Feb 22 | Jan 9 | Dec 17 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 12 | Apr 3 | Mar 21 | Mar 7 | Feb 28 | Feb 22 | Feb 15 | Feb 1 | Jan 9 |
| 32°F | Feb 26 | Feb 17 | Feb 6 | Jan 30 | Jan 16 | Jan 6 | Dec 31 | Dec 24 | Dec 11 |
| 28°F | Feb 22 | Feb 11 | Feb 1 | Jan 18 | Jan 9 | Jan 2 | Dec 29 | Dec 25 | Dec 17 |
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 5 | Dec 1 | Jan 4 |
| Freeze (32°F) | Nov 25 | Dec 25 | Feb 12 |
| Hard (28°F) | Dec 14 | Jan 6 | Feb 17 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 5 | Nov 16 | Nov 21 | Nov 27 | Dec 1 | Dec 7 | Dec 12 | Dec 19 | Jan 4 |
| 32°F | Nov 25 | Dec 4 | Dec 13 | Dec 17 | Dec 25 | Dec 31 | Jan 7 | Jan 26 | Feb 12 |
| 28°F | Dec 14 | Dec 22 | Dec 29 | Dec 31 | Jan 6 | Jan 13 | Jan 24 | Feb 4 | Feb 17 |
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: San Luis Obispo Poly, Ca, about 0.4 miles away@if(!empty($station['elevation_ft'])), at 308 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 California Polytechnic State University, CA?
On average, the last spring frost (32°F) around California Polytechnic State University, CA is about Jan 16. In cooler years it can run later, so for a safer bet many gardeners wait until Dec 11.
When is the first frost in the fall?
The first fall frost around California Polytechnic State University, CA typically arrives about Dec 25. 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 Jan 16 on average, or Dec 11 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 349 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 93407 Planting calendar → California frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026