Frost dates for Iowa City, IA
At Iowa City, the median last spring frost (32°F) is Apr 29 and the median first fall frost is Oct 9, for a typical growing season of 162 days. For a 90% chance that the last frost has passed, wait until May 14. Nearby ZIP codes are in USDA hardiness zone 5b.
- Apr 29Last spring frost (median)50% chance of 32°F after this date
- May 14Safer planting date10% chance of 32°F after this date
- Oct 9First fall frost (median)50% chance of 32°F by this date
- 162 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 24 | May 7 | May 21 |
| 32°F | Apr 14 | Apr 29 | May 14 |
| 28°F | Apr 3 | Apr 18 | May 5 |
| 24°F | Mar 22 | Apr 6 | Apr 25 |
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 17 | Oct 1 | Oct 12 |
| 32°F | Sep 25 | Oct 9 | Oct 22 |
| 28°F | Oct 3 | Oct 20 | Nov 1 |
| 24°F | Oct 17 | Oct 30 | Nov 11 |
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 | 127 days | 146 days | 163 days |
| 32°F | 143 days | 162 days | 185 days |
| 28°F | 161 days | 182 days | 203 days |
| 24°F | 183 days | 205 days | 225 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 |
|---|---|---|---|
| 52240 | 5b | -15 to -10°F | 2 km |
| 52235 | 5b | -15 to -10°F | 4 km |
| 52755 | 5b | -15 to -10°F | 16 km |
| 52327 | 5b | -15 to -10°F | 16 km |
| 52358 | 5b | -15 to -10°F | 18 km |
| 52776 | 5b | -15 to -10°F | 20 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 USC00134101, at 41.6092, -91.5050, elevation 195 m (640 ft).
- Data quality: Standard (24+ years of data), 29 years of freeze data.
- Average days per year at or below 32°F: 130.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Iowa City Muni Airport (4 km)
- Cedar Rapids Muni Airport (35 km)
- Tipton (37 km)
- Columbus Junction (39 km)
- Washington (40 km)
- Muscatine 2n (41 km)
- Williamsburg 1e (41 km)
- Muscatine (42 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.