Frost dates for Saint Helena, CA
At Saint Helena, the median last spring frost (32°F) is Feb 3 and the median first fall frost is Dec 4, for a typical growing season of 306 days. For a 90% chance that the last frost has passed, wait until Mar 13. Nearby ZIP codes are in USDA hardiness zone 9b.
- Feb 3Last spring frost (median)50% chance of 32°F after this date
- Mar 13Safer planting date10% chance of 32°F after this date
- Dec 4First fall frost (median)50% chance of 32°F by this date
- 306 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | Feb 14 | Mar 19 | Apr 17 |
| 32°F | Dec 28 | Feb 3 | Mar 13 |
| 28°F | Dec 11 | Jan 5 | Feb 9 |
| 24°F | Dec 3 | Dec 28 | Feb 2 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Oct 31 | Nov 18 | Dec 5 |
| 32°F | Nov 14 | Dec 4 | Jan 1 |
| 28°F | Nov 27 | Dec 17 | Jan 18 |
| 24°F | Dec 1 | Dec 23 | Jan 25 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 210 days | 243 days | 283 days |
| 32°F | 260 days | 306 days | 341 days |
| 28°F | 317 days | 349 days | 365 days |
| 24°F | 349 days | 365 days | 365 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 97% |
| 28°F | 65% |
| 24°F | 15% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 94573 | 9b | 25 to 30°F | 6 km |
| 94562 | 9b | 25 to 30°F | 10 km |
| 95452 | 9b | 25 to 30°F | 10 km |
| 95409 | 9b | 25 to 30°F | 11 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00047643, at 38.5067, -122.4714, elevation 69 m (225 ft).
- Data quality: Standard (24+ years of data), 26 years of freeze data.
- Average days per year at or below 32°F: 14.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Angwin Pacific Union College (8 km)
- Calistoga (15 km)
- Santa Rosa (22 km)
- Sonoma (23 km)
- Santa Rosa Sonoma Co Airport (29 km)
- Petaluma Airport (30 km)
- Markley Cove (30 km)
- Napa State Hospital (31 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.