Frost dates for Duluth NWS, MN
At Duluth NWS, the median last spring frost (32°F) is May 18 and the median first fall frost is Oct 1, for a typical growing season of 135 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 18Last 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
- 135 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 16 | Jun 1 | Jun 17 |
| 32°F | May 2 | May 18 | Jun 3 |
| 28°F | Apr 22 | May 4 | May 21 |
| 24°F | Apr 10 | Apr 25 | May 8 |
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 8 | Sep 22 | Oct 4 |
| 32°F | Sep 19 | Oct 1 | Oct 14 |
| 28°F | Sep 29 | Oct 12 | Oct 27 |
| 24°F | Oct 10 | Oct 25 | Nov 7 |
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 | 90 days | 112 days | 131 days |
| 32°F | 113 days | 135 days | 155 days |
| 28°F | 136 days | 159 days | 179 days |
| 24°F | 160 days | 181 days | 201 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 |
|---|---|---|---|
| 55811 | 4b | -25 to -20°F | 1 km |
| 55810 | 4b | -25 to -20°F | 10 km |
| 55779 | 4a | -30 to -25°F | 20 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 USC00212250, at 46.8367, -92.2108, elevation 437 m (1,433 ft).
- Data quality: Estimated from nearby stations (2+ years), 8 years of freeze data.
- Average days per year at or below 32°F: 184.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Duluth (0 km)
- Duluth Harbor Station (12 km)
- Island Lake 4e (23 km)
- Cloquet (28 km)
- Cotton (42 km)
- Two Harbors (46 km)
- Two Harbors 7nw (50 km)
- Floodwood 3 NE (52 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.