Last spring frost
Dec 29
Frost Dates for San Mateo, CA
First fall frost
Dec 26
Growing season
365 days
Hardiness zone
10a
In an average year around San Mateo, CA, the last spring frost (32°F) is about Dec 29 and the first fall frost is about Dec 26, giving roughly a 365-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) | Feb 14 | Jan 8 | Dec 16 |
| Freeze (32°F) | Jan 13 | Dec 29 | Dec 11 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 14 | Jan 30 | Jan 22 | Jan 15 | Jan 8 | Jan 3 | Dec 30 | Dec 25 | Dec 16 |
| 32°F | Jan 13 | Jan 7 | Jan 3 | Dec 31 | Dec 29 | Dec 26 | Dec 23 | Dec 17 | Dec 11 |
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) | Dec 5 | Dec 24 | Jan 24 |
| Freeze (32°F) | Dec 11 | Dec 26 | Jan 13 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Dec 5 | Dec 10 | Dec 15 | Dec 19 | Dec 24 | Dec 28 | Jan 1 | Jan 9 | Jan 24 |
| 32°F | Dec 11 | Dec 17 | Dec 21 | Dec 24 | Dec 26 | Dec 30 | Jan 1 | Jan 6 | Jan 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: San Francisco Intl Ap, Ca, about 3.9 miles away@if(!empty($station['elevation_ft'])), at 8 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 San Mateo, CA?
On average, the last spring frost (32°F) around San Mateo, CA is about Dec 29. 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 San Mateo, CA typically arrives about Dec 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 Dec 29 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 365 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 94401 Planting calendar → California frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026