Frost dates for 49918Copper Harbor, MI
The average last spring frost in Copper Harbor is May 10 and the average first fall frost is October 21, giving a typical growing season of about 161 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 10
- Average first fall frost
- Oct 21
- Growing season
- 161 days
Safer after Jun 2 (1-in-10 risk)
Possible by Oct 3 (1-in-10 risk)
Last frost typically in 195 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | May 9 · May 27 · Jun 13 | Sep 21 · Oct 6 · Oct 21 | 131 days | 100% |
| Frost / freeze (32°F) | Apr 26 · May 10 · Jun 2 | Oct 3 · Oct 21 · Nov 5 | 161 days | 100% |
| Hard freeze (28°F) | Apr 14 · Apr 27 · May 14 | Oct 19 · Nov 3 · Nov 18 | 187 days | 100% |
Planting calendar for Copper Harbor
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Apr 9 – Jun 15 |
| Tomatoes | Transplant outdoors | May 26 – Jul 1 |
| Peppers | Start seeds indoors | Apr 9 – May 10 |
| Peppers | Transplant outdoors | Jun 9 – Jul 10 |
| Eggplant | Start seeds indoors | Apr 26 – May 25 |
| Eggplant | Transplant outdoors | Jun 9 – Jul 10 |
| Cucumbers | Sow outdoors | Jun 9 – Jul 11 |
| Summer squash | Sow outdoors | May 26 – Jul 10 |
| Winter squash & pumpkins | Sow outdoors | Jun 9 – Jul 10 |
| Snap beans | Sow outdoors | May 26 – Aug 3 |
| Sweet corn | Sow outdoors | May 26 – Jul 1 |
| Watermelon & cantaloupe | Sow outdoors | Jun 9 – Jul 10 |
| Okra | Sow outdoors | Jun 2 – Jun 25 |
| Peas | Sow outdoors (spring) | Apr 9 – May 25 |
| Potatoes | Plant outdoors (spring) | Apr 9 – Jun 9 |
| Onions | Start seeds indoors (spring) | Feb 26 – Mar 25 |
| Onions | Transplant outdoors (spring) | Apr 26 – May 25 |
| Broccoli | Start seeds indoors (spring) | Mar 22 – Apr 25 |
| Broccoli | Transplant outdoors (spring) | Apr 26 – May 25 |
| Broccoli | Start seeds indoors (fall) | Jun 21 – Jul 1 |
| Broccoli | Transplant outdoors (fall) | Jul 21 – Aug 1 |
| Cabbage | Start seeds indoors (spring) | Mar 12 – Apr 9 |
| Cabbage | Transplant outdoors (spring) | Apr 9 – May 10 |
| Cabbage | Start seeds indoors (fall) | Jun 11 – Jul 11 |
| Cabbage | Transplant outdoors (fall) | Jul 11 – Aug 11 |
| Leaf lettuce | Sow outdoors (spring) | Apr 9 – Jun 25 |
| Leaf lettuce | Sow outdoors (fall) | Jul 11 – Aug 27 |
| Spinach | Sow outdoors (spring) | Apr 2 – May 16 |
| Spinach | Sow outdoors (fall) | Jul 28 – Sep 1 |
| Radishes | Sow outdoors (spring) | Apr 9 – May 30 |
| Radishes | Sow outdoors (fall) | Jul 11 – Sep 11 |
| Kale | Sow outdoors (spring) | Apr 26 – May 16 |
| Kale | Sow outdoors (fall) | Jul 4 – Aug 11 |
| Carrots | Sow outdoors (spring) | May 10 – Jun 25 |
| Carrots | Sow outdoors (fall) | Jun 11 – Jul 27 |
| Garlic | Plant outdoors (fall) | Oct 11 – Nov 11 |
Where these dates come from
ZIP code 49918 is matched to the NOAA station Copper Harbor, MI, 0.4 km away, at 626 ft elevation (12 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Copper Harbor, MI (used) | 626 ft | May 10 | Oct 21 |
| Copper Harbor Ft Wilkins, MI | 625 ft | May 20 | Oct 15 |
| Hancock Houghton Co Ap, MI | 1,063 ft | May 17 | Oct 1 |
| Jacobsville, MI | 650 ft | Jun 1 | Sep 23 |
Frost dates near Copper Harbor
- Mohawk, MI 49950 · last May 17, first Oct 1
- Ahmeek, MI 49901 · last May 17, first Oct 1
- Copper City, MI 49917 · last May 17, first Oct 1
- Allouez, MI 49805 · last May 17, first Oct 1
- Lake Linden, MI 49945 · last May 17, first Oct 1
- Kearsarge, MI 49942 · last May 17, first Oct 1
- Calumet, MI 49913 · last May 17, first Oct 1
- Hubbell, MI 49934 · last May 17, first Oct 1
Frequently asked questions
- When is the last frost in Copper Harbor, MI?
- For ZIP code 49918, the average last spring frost (32°F) is May 10, based on NOAA 1991-2020 climate normals for the Copper Harbor, MI weather station. There is a 1-in-10 chance of a frost after June 2.
- When is the first frost in Copper Harbor, MI?
- The average first fall frost (32°F) is October 21. There is a 1-in-10 chance of frost by October 3, so tender plants are at risk from that point on.
- How long is the growing season in 49918?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 161 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.