Frost dates for Grinnell 3 SW, IA
At Grinnell 3 SW, the median last spring frost (32°F) is May 3 and the median first fall frost is Oct 6, for a typical growing season of 155 days. For a 90% chance that the last frost has passed, wait until May 17. Nearby ZIP codes are in USDA hardiness zones 5a to 5b.
- May 3Last spring frost (median)50% chance of 32°F after this date
- May 17Safer planting date10% chance of 32°F after this date
- Oct 6First fall frost (median)50% chance of 32°F by this date
- 155 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 30 | May 13 | May 27 |
| 32°F | Apr 19 | May 3 | May 17 |
| 28°F | Apr 9 | Apr 23 | May 9 |
| 24°F | Mar 30 | Apr 11 | Apr 30 |
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 10 |
| 32°F | Sep 22 | Oct 6 | Oct 20 |
| 28°F | Oct 1 | Oct 17 | Oct 29 |
| 24°F | Oct 11 | Oct 26 | Nov 6 |
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 | 118 days | 136 days | 155 days |
| 32°F | 136 days | 155 days | 175 days |
| 28°F | 152 days | 175 days | 195 days |
| 24°F | 172 days | 194 days | 215 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 |
|---|---|---|---|
| 50112 | 5b | -15 to -10°F | 3 km |
| 50157 | 5a | -20 to -15°F | 16 km |
| 50153 | 5b | -15 to -10°F | 17 km |
| 50242 | 5b | -15 to -10°F | 18 km |
| 50106 | 5a | -20 to -15°F | 19 km |
| 50251 | 5b | -15 to -10°F | 20 km |
| 50171 | 5b | -15 to -10°F | 24 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 USC00133473, at 41.7200, -92.7489, elevation 276 m (905 ft).
- Data quality: Standard (24+ years of data), 29 years of freeze data.
- Average days per year at or below 32°F: 157.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Newton (23 km)
- Toledo 3n (38 km)
- Marshalltown (41 km)
- Belle Plaine (43 km)
- Oskaloosa (45 km)
- Marshalltown Muni Airport (46 km)
- Des Moines 17 E (48 km)
- Knoxville (53 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.