Frost dates for Idaho City, ID
At Idaho City, the median last spring frost (32°F) is Jun 17 and the median first fall frost is Sep 5, for a typical growing season of 80 days. For a 90% chance that the last frost has passed, wait until Jul 4. Nearby ZIP codes are in USDA hardiness zone 6b.
- Jun 17Last spring frost (median)50% chance of 32°F after this date
- Jul 4Safer planting date10% chance of 32°F after this date
- Sep 5First fall frost (median)50% chance of 32°F by this date
- 80 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 |
|---|---|---|---|
| 32°F | May 30 | Jun 17 | Jul 4 |
| 28°F | May 7 | May 22 | Jun 14 |
| 24°F | Apr 18 | May 3 | May 18 |
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 |
|---|---|---|---|
| 32°F | Aug 23 | Sep 5 | Sep 21 |
| 28°F | Sep 3 | Sep 19 | Oct 5 |
| 24°F | Sep 16 | Oct 3 | Oct 19 |
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 | 30 days | 52 days | 72 days |
| 32°F | 57 days | 80 days | 105 days |
| 28°F | 90 days | 117 days | 140 days |
| 24°F | 128 days | 152 days | 175 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 83631 | 6b | -5 to 0°F | 7 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 USC00104442, at 43.8383, -115.8319, elevation 1208 m (3,965 ft).
- Data quality: Representative (10+ years), 22 years of freeze data.
- Average days per year at or below 32°F: 224.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Arrowrock Dam (28 km)
- Garden Valley (31 km)
- Boise 7 N (32 km)
- Lowman (32 km)
- Boise Lucky Peak Dam (39 km)
- Boise Air Terminal (45 km)
- Emmett 2 E (51 km)
- Ola (52 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.