Last spring frost
Jan 9
Frost Dates for Riverside, CA
First fall frost
Dec 25
Growing season
353 days
Hardiness zone
10a
In an average year around Riverside, CA, the last spring frost (32°F) is about Jan 9 and the first fall frost is about Dec 25, giving roughly a 353-day growing season. To be safe most years, wait until Dec 16 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) | Mar 22 | Feb 19 | Jan 8 |
| Freeze (32°F) | Feb 25 | Jan 9 | Dec 16 |
| Hard (28°F) | Jan 16 | Dec 31 | Dec 13 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Mar 22 | Mar 11 | Mar 4 | Feb 27 | Feb 19 | Feb 10 | Feb 2 | Jan 21 | Jan 8 |
| 32°F | Feb 25 | Feb 6 | Jan 25 | Jan 17 | Jan 9 | Jan 4 | Dec 31 | Dec 25 | Dec 16 |
| 28°F | Jan 16 | Jan 8 | Jan 5 | Jan 1 | Dec 31 | Dec 28 | Dec 25 | Dec 19 | Dec 13 |
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 15 | Dec 6 | Jan 1 |
| Freeze (32°F) | Dec 1 | Dec 25 | Jan 27 |
| Hard (28°F) | Nov 30 | Dec 29 | Jan 13 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 15 | Nov 24 | Nov 29 | Dec 2 | Dec 6 | Dec 11 | Dec 15 | Dec 21 | Jan 1 |
| 32°F | Dec 1 | Dec 10 | Dec 15 | Dec 20 | Dec 25 | Dec 30 | Jan 4 | Jan 11 | Jan 27 |
| 28°F | Nov 30 | Dec 13 | Dec 20 | Dec 25 | Dec 29 | Dec 31 | Jan 2 | Jan 7 | 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: Riverside Fire Stn 3, Ca, about 1.7 miles away@if(!empty($station['elevation_ft'])), at 840 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 Riverside, CA?
On average, the last spring frost (32°F) around Riverside, CA is about Jan 9. In cooler years it can run later, so for a safer bet many gardeners wait until Dec 16.
When is the first frost in the fall?
The first fall frost around Riverside, 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 9 on average, or Dec 16 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 353 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 92506 Planting calendar → California frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026