Last spring frost
May 20
Frost Dates for Copper Harbor, MI
First fall frost
Oct 15
Growing season
148 days
Hardiness zone
6a
In an average year around Copper Harbor, MI, the last spring frost (32°F) is about May 20 and the first fall frost is about Oct 15, giving roughly a 148-day growing season. To be safe most years, wait until May 3 before setting out tender plants.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Jun 16 | Jun 2 | May 19 |
| Freeze (32°F) | Jun 3 | May 20 | May 3 |
| Hard (28°F) | May 21 | May 4 | Apr 23 |
| Severe (24°F) | May 6 | Apr 24 | Apr 11 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 16 | Jun 11 | Jun 7 | Jun 4 | Jun 2 | May 31 | May 28 | May 25 | May 19 |
| 32°F | Jun 3 | May 30 | May 26 | May 22 | May 20 | May 16 | May 12 | May 8 | May 3 |
| 28°F | May 21 | May 15 | May 10 | May 6 | May 4 | May 2 | Apr 30 | Apr 27 | Apr 23 |
| 24°F | May 6 | May 1 | Apr 29 | Apr 27 | Apr 24 | Apr 21 | Apr 19 | Apr 16 | Apr 11 |
| 20°F | Apr 25 | Apr 22 | Apr 19 | Apr 16 | Apr 14 | Apr 10 | Apr 7 | Apr 5 | Apr 1 |
| 16°F | Apr 19 | Apr 14 | Apr 11 | Apr 8 | Apr 6 | Apr 4 | Apr 1 | Mar 30 | Mar 24 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Sep 19 | Oct 3 | Oct 16 |
| Freeze (32°F) | Sep 30 | Oct 15 | Oct 30 |
| Hard (28°F) | Oct 13 | Oct 29 | Nov 11 |
| Severe (24°F) | Oct 27 | Nov 7 | Nov 20 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 19 | Sep 24 | Sep 28 | Sep 30 | Oct 3 | Oct 5 | Oct 8 | Oct 11 | Oct 16 |
| 32°F | Sep 30 | Oct 5 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 21 | Oct 25 | Oct 30 |
| 28°F | Oct 13 | Oct 19 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 2 | Nov 5 | Nov 11 |
| 24°F | Oct 27 | Oct 31 | Nov 2 | Nov 5 | Nov 7 | Nov 10 | Nov 12 | Nov 15 | Nov 20 |
| 20°F | Nov 4 | Nov 8 | Nov 11 | Nov 14 | Nov 17 | Nov 19 | Nov 22 | Nov 26 | Dec 1 |
| 16°F | Nov 12 | Nov 17 | Nov 19 | Nov 23 | Nov 25 | Nov 28 | Dec 1 | Dec 5 | Dec 11 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Copper Harbor Ft Wilkins, Mi, about 2.6 miles away@if(!empty($station['elevation_ft'])), at 625 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
When is the last frost in Copper Harbor, MI?
On average, the last spring frost (32°F) around Copper Harbor, MI is about May 20. In cooler years it can run later, so for a safer bet many gardeners wait until May 3.
When is the first frost in the fall?
The first fall frost around Copper Harbor, MI typically arrives about Oct 15. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around May 20 on average, or May 3 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 148 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 49918 Planting calendar → Michigan frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026