Frost dates for Grundy Center, IA
At Grundy Center, 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 160 days. For a 90% chance that the last frost has passed, wait until May 12. Nearby ZIP codes are in USDA hardiness zone 5a.
- Apr 29Last spring frost (median)50% chance of 32°F after this date
- May 12Safer planting date10% chance of 32°F after this date
- Oct 9First fall frost (median)50% chance of 32°F by this date
- 160 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 25 | May 7 | May 21 |
| 32°F | Apr 15 | Apr 29 | May 12 |
| 28°F | Apr 4 | Apr 19 | May 3 |
| 24°F | Mar 24 | Apr 9 | Apr 24 |
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 16 | Sep 30 | Oct 11 |
| 32°F | Sep 25 | Oct 9 | Oct 20 |
| 28°F | Oct 5 | Oct 18 | Oct 30 |
| 24°F | Oct 16 | Oct 28 | Nov 10 |
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 | 126 days | 144 days | 161 days |
| 32°F | 142 days | 160 days | 180 days |
| 28°F | 159 days | 180 days | 200 days |
| 24°F | 179 days | 200 days | 220 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 |
|---|---|---|---|
| 50638 | 5a | -20 to -15°F | 3 km |
| 50657 | 5a | -20 to -15°F | 7 km |
| 50642 | 5a | -20 to -15°F | 10 km |
| 50669 | 5a | -20 to -15°F | 12 km |
| 50652 | 5a | -20 to -15°F | 12 km |
| 50624 | 5a | -20 to -15°F | 14 km |
| 50680 | 5a | -20 to -15°F | 16 km |
| 50673 | 5a | -20 to -15°F | 18 km |
| 50635 | 5a | -20 to -15°F | 19 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 USC00133487, at 42.3647, -92.7594, elevation 300 m (985 ft).
- Data quality: Standard (24+ years of data), 30 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
- Eldora (28 km)
- Marshalltown Muni Airport (31 km)
- Marshalltown (36 km)
- Waterloo Muni Airport (36 km)
- Toledo 3n (39 km)
- Allison (43 km)
- Iowa Falls (44 km)
- Hampton (57 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.