Frost dates for Charles City, IA
At Charles City, the median last spring frost (32°F) is Apr 30 and the median first fall frost is Oct 6, for a typical growing season of 157 days. For a 90% chance that the last frost has passed, wait until May 14. Nearby ZIP codes are in USDA hardiness zone 5a.
- Apr 30Last spring frost (median)50% chance of 32°F after this date
- May 14Safer planting date10% chance of 32°F after this date
- Oct 6First fall frost (median)50% chance of 32°F by this date
- 157 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 | Apr 27 | May 9 | May 22 |
| 32°F | Apr 15 | Apr 30 | May 14 |
| 28°F | Apr 5 | Apr 21 | May 6 |
| 24°F | Mar 26 | Apr 9 | Apr 29 |
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 | Sep 15 | Sep 27 | Oct 9 |
| 32°F | Sep 21 | Oct 6 | Oct 19 |
| 28°F | Oct 3 | Oct 17 | Oct 29 |
| 24°F | Oct 12 | Oct 27 | Nov 9 |
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 | 123 days | 141 days | 159 days |
| 32°F | 140 days | 157 days | 178 days |
| 28°F | 157 days | 178 days | 198 days |
| 24°F | 177 days | 198 days | 218 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 |
|---|---|---|---|
| 50616 | 5a | -20 to -15°F | 2 km |
| 50620 | 5a | -20 to -15°F | 13 km |
| 50435 | 5a | -20 to -15°F | 13 km |
| 50658 | 5a | -20 to -15°F | 16 km |
| 50653 | 5a | -20 to -15°F | 20 km |
| 50468 | 5a | -20 to -15°F | 23 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 USC00131402, at 43.0603, -92.6717, elevation 303 m (993 ft).
- Data quality: Standard (24+ years of data), 28 years of freeze data.
- Average days per year at or below 32°F: 154.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Osage (27 km)
- New Hampton (29 km)
- Allison (36 km)
- Tripoli (44 km)
- Mason City (44 km)
- Mason City Muni Airport (54 km)
- Hampton (55 km)
- Cresco 1 NE (59 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.