Last spring frost
Jan 6
Frost Dates for Casa de Oro-Mount Helix, CA
First fall frost
Dec 21
Growing season
350 days
Hardiness zone
10b
In an average year around Casa de Oro-Mount Helix, CA, the last spring frost (32°F) is about Jan 6 and the first fall frost is about Dec 21, giving roughly a 350-day growing season. To be safe most years, wait until Dec 13 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 3 | Feb 6 | Jan 6 |
| Freeze (32°F) | Feb 7 | Jan 6 | Dec 13 |
| Hard (28°F) | Jan 15 | Dec 31 | Dec 8 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Mar 3 | Feb 25 | Feb 18 | Feb 12 | Feb 6 | Jan 31 | Jan 25 | Jan 16 | Jan 6 |
| 32°F | Feb 7 | Jan 30 | Jan 21 | Jan 12 | Jan 6 | Dec 31 | Dec 28 | Dec 22 | Dec 13 |
| 28°F | Jan 15 | Jan 10 | Jan 6 | Jan 3 | Dec 31 | Dec 29 | Dec 23 | Dec 15 | 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) | Nov 18 | Dec 6 | Dec 29 |
| Freeze (32°F) | Dec 1 | Dec 21 | Jan 15 |
| Hard (28°F) | Dec 7 | Dec 30 | Jan 14 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 18 | Nov 25 | Nov 29 | Dec 2 | Dec 6 | Dec 10 | Dec 15 | Dec 20 | Dec 29 |
| 32°F | Dec 1 | Dec 7 | Dec 12 | Dec 17 | Dec 21 | Dec 25 | Dec 30 | Jan 4 | Jan 15 |
| 28°F | Dec 7 | Dec 14 | Dec 20 | Dec 27 | Dec 30 | Jan 1 | Jan 6 | Jan 9 | Jan 14 |
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: El Cajon, Ca, about 4.9 miles away@if(!empty($station['elevation_ft'])), at 495 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 Casa de Oro-Mount Helix, CA?
On average, the last spring frost (32°F) around Casa de Oro-Mount Helix, CA is about Jan 6. In cooler years it can run later, so for a safer bet many gardeners wait until Dec 13.
When is the first frost in the fall?
The first fall frost around Casa de Oro-Mount Helix, CA typically arrives about Dec 21. 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 6 on average, or Dec 13 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 350 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 91941 Planting calendar → California frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026