Last spring frost
Apr 30
Frost Dates for Potrero, CA
First fall frost
Oct 26
Growing season
174 days
Hardiness zone
9a
In an average year around Potrero, CA, the last spring frost (32°F) is about Apr 30 and the first fall frost is about Oct 26, giving roughly a 174-day growing season. To be safe most years, wait until Apr 9 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 29 | Jun 3 | May 3 |
| Freeze (32°F) | Jun 1 | Apr 30 | Apr 9 |
| Hard (28°F) | Apr 28 | Apr 2 | Feb 23 |
| Severe (24°F) | Mar 28 | Feb 13 | Dec 29 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 29 | Jun 20 | Jun 13 | Jun 7 | Jun 3 | May 29 | May 23 | May 15 | May 3 |
| 32°F | Jun 1 | May 19 | May 13 | May 4 | Apr 30 | Apr 25 | Apr 20 | Apr 16 | Apr 9 |
| 28°F | Apr 28 | Apr 17 | Apr 11 | Apr 6 | Apr 2 | Mar 28 | Mar 18 | Mar 2 | Feb 23 |
| 24°F | Mar 28 | Mar 10 | Feb 27 | Feb 19 | Feb 13 | Feb 5 | Jan 30 | Jan 16 | Dec 29 |
| 20°F | Feb 24 | Feb 13 | Feb 3 | Jan 27 | Jan 16 | Jan 6 | Dec 28 | Dec 17 | Dec 8 |
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 2 | Oct 2 | Oct 23 |
| Freeze (32°F) | Sep 30 | Oct 26 | Nov 12 |
| Hard (28°F) | Oct 22 | Nov 14 | Dec 5 |
| Severe (24°F) | Nov 11 | Dec 5 | Jan 8 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 2 | Sep 14 | Sep 23 | Sep 28 | Oct 2 | Oct 7 | Oct 12 | Oct 17 | Oct 23 |
| 32°F | Sep 30 | Oct 9 | Oct 15 | Oct 21 | Oct 26 | Oct 30 | Nov 2 | Nov 6 | Nov 12 |
| 28°F | Oct 22 | Nov 1 | Nov 4 | Nov 9 | Nov 14 | Nov 19 | Nov 24 | Dec 1 | Dec 5 |
| 24°F | Nov 11 | Nov 21 | Nov 29 | Dec 2 | Dec 5 | Dec 10 | Dec 15 | Dec 25 | Jan 8 |
| 20°F | Dec 1 | Dec 8 | Dec 13 | Dec 19 | Dec 27 | Jan 2 | Jan 12 | Jan 28 | Feb 13 |
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: Campo, Ca, about 7.5 miles away@if(!empty($station['elevation_ft'])), at 2,630 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 Potrero, CA?
On average, the last spring frost (32°F) around Potrero, CA is about Apr 30. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 9.
When is the first frost in the fall?
The first fall frost around Potrero, CA typically arrives about Oct 26. 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 Apr 30 on average, or Apr 9 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 174 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 91963 Planting calendar → California frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026