Frost dates for Ironwood #2, MI
At Ironwood #2, the median last spring frost (32°F) is May 19 and the median first fall frost is Sep 28, for a typical growing season of 130 days. For a 90% chance that the last frost has passed, wait until Jun 3. Nearby ZIP codes are in USDA hardiness zones 4a to 4b.
- May 19Last spring frost (median)50% chance of 32°F after this date
- Jun 3Safer planting date10% chance of 32°F after this date
- Sep 28First fall frost (median)50% chance of 32°F by this date
- 130 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 | May 18 | May 31 | Jun 17 |
| 32°F | May 2 | May 19 | Jun 3 |
| 28°F | Apr 23 | May 5 | May 21 |
| 24°F | Apr 13 | Apr 26 | May 9 |
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 1 | Sep 17 | Sep 30 |
| 32°F | Sep 12 | Sep 28 | Oct 10 |
| 28°F | Sep 23 | Oct 9 | Oct 24 |
| 24°F | Oct 7 | Oct 24 | 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 | 81 days | 105 days | 126 days |
| 32°F | 108 days | 130 days | 152 days |
| 28°F | 132 days | 154 days | 176 days |
| 24°F | 157 days | 178 days | 198 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 |
|---|---|---|---|
| 49938 | 4b | -25 to -20°F | 7 km |
| 49911 | 4b | -25 to -20°F | 7 km |
| 49959 | 4a | -30 to -25°F | 11 km |
| 49968 | 4a | -30 to -25°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 USC00204105, at 46.4653, -90.1383, elevation 463 m (1,520 ft).
- Data quality: Estimated from nearby stations (2+ years), 2 years of freeze data.
- Average days per year at or below 32°F: 202.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Ironwood (4 km)
- Bergland Dam (47 km)
- Paulding (74 km)
- Ontonagon 6 SE (82 km)
- Greenland 6n (91 km)
- Watton 2wsw (115 km)
- Covington 1nnw (123 km)
- Baraga 7nw (123 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.