Frost dates for Ironwood, MI
At Ironwood, the median last spring frost (32°F) is May 20 and the median first fall frost is Oct 1, for a typical growing season of 132 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 20Last spring frost (median)50% chance of 32°F after this date
- Jun 3Safer planting date10% chance of 32°F after this date
- Oct 1First fall frost (median)50% chance of 32°F by this date
- 132 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 17 | May 31 | Jun 14 |
| 32°F | May 2 | May 20 | Jun 3 |
| 28°F | Apr 22 | May 6 | May 23 |
| 24°F | Apr 11 | Apr 26 | May 12 |
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 5 | Sep 20 | Oct 3 |
| 32°F | Sep 17 | Oct 1 | Oct 15 |
| 28°F | Sep 28 | Oct 12 | Oct 28 |
| 24°F | Oct 9 | Oct 26 | Nov 8 |
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 | 89 days | 109 days | 130 days |
| 32°F | 111 days | 132 days | 156 days |
| 28°F | 134 days | 157 days | 178 days |
| 24°F | 159 days | 182 days | 203 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
Closest ZIP codes (each is closer to another station)
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 54525 | 4b | -25 to -20°F | 4 km |
| 49938 | 4b | -25 to -20°F | 8 km |
| 49911 | 4b | -25 to -20°F | 11 km |
| 54534 | 4a | -30 to -25°F | 13 km |
| 54550 | 4a | -30 to -25°F | 14 km |
| 49959 | 4a | -30 to -25°F | 15 km |
| 54536 | 4a | -30 to -25°F | 17 km |
| 49968 | 4a | -30 to -25°F | 23 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 USC00204104, at 46.4656, -90.1892, elevation 436 m (1,430 ft).
- Data quality: Standard (24+ years of data), 30 years of freeze data.
- Average days per year at or below 32°F: 187.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Ironwood #2 (4 km)
- Bergland Dam (51 km)
- Paulding (78 km)
- Ontonagon 6 SE (85 km)
- Greenland 6n (95 km)
- Watton 2wsw (119 km)
- Covington 1nnw (126 km)
- Baraga 7nw (127 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.