Frost dates for Washington, IA
At Washington, the median last spring frost (32°F) is Apr 28 and the median first fall frost is Oct 11, for a typical growing season of 165 days. For a 90% chance that the last frost has passed, wait until May 11. Nearby ZIP codes are in USDA hardiness zone 5b.
- Apr 28Last spring frost (median)50% chance of 32°F after this date
- May 11Safer planting date10% chance of 32°F after this date
- Oct 11First fall frost (median)50% chance of 32°F by this date
- 165 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 6 | May 19 |
| 32°F | Apr 13 | Apr 28 | May 11 |
| 28°F | Apr 3 | Apr 17 | May 2 |
| 24°F | Mar 22 | Apr 6 | Apr 21 |
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 13 |
| 32°F | Sep 25 | Oct 11 | Oct 24 |
| 28°F | Oct 7 | Oct 22 | Nov 1 |
| 24°F | Oct 19 | Oct 31 | Nov 13 |
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 | 129 days | 147 days | 164 days |
| 32°F | 147 days | 165 days | 186 days |
| 28°F | 165 days | 187 days | 206 days |
| 24°F | 188 days | 208 days | 229 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 |
|---|---|---|---|
| 52353 | 5b | -15 to -10°F | 2 km |
| 52359 | 5b | -15 to -10°F | 12 km |
| 52201 | 5b | -15 to -10°F | 14 km |
| 52654 | 5b | -15 to -10°F | 16 km |
| 52540 | 5b | -15 to -10°F | 17 km |
| 52248 | 5b | -15 to -10°F | 20 km |
| 52356 | 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 USC00138688, at 41.2825, -91.7078, elevation 209 m (687 ft).
- Data quality: Standard (24+ years of data), 27 years of freeze data.
- Average days per year at or below 32°F: 140.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Columbus Junction (29 km)
- Fairfield (36 km)
- Mount Pleasant 1 SSW (39 km)
- Iowa City (40 km)
- Iowa City Muni Airport (41 km)
- Sigourney (44 km)
- Williamsburg 1e (49 km)
- Muscatine (55 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.