Frost dates for 49801Iron Mountain, MI
The average last spring frost in Iron Mountain is May 25 and the average first fall frost is September 24, giving a typical growing season of about 121 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 25
- Average first fall frost
- Sep 24
- Growing season
- 121 days
Safer after Jun 6 (1-in-10 risk)
Possible by Sep 8 (1-in-10 risk)
Last frost typically in 211 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 24 · Jun 5 · Jun 22 | Aug 24 · Sep 12 · Sep 27 | 97 days | 100% |
| Frost / freeze (32°F) | May 10 · May 25 · Jun 6 | Sep 8 · Sep 24 · Oct 7 | 121 days | 100% |
| Hard freeze (28°F) | Apr 28 · May 11 · May 26 | Sep 21 · Oct 5 · Oct 19 | 145 days | 100% |
Planting calendar for Iron Mountain
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 24 – Jun 30 |
| Tomatoes | Transplant outdoors | Jun 10 – Jun 4 |
| Peppers | Start seeds indoors | Apr 24 – May 25 |
| Peppers | Transplant outdoors | Jun 24 – Jul 25 |
| Eggplant | Start seeds indoors | May 11 – Jun 9 |
| Eggplant | Transplant outdoors | Jun 24 – Jul 25 |
| Cucumbers | Sow outdoors | Jun 24 – Jun 14 |
| Summer squash | Sow outdoors | Jun 10 – Jul 25 |
| Winter squash & pumpkins | Sow outdoors | Jun 24 – Jul 25 |
| Snap beans | Sow outdoors | Jun 10 – Jul 7 |
| Sweet corn | Sow outdoors | Jun 10 – Jun 4 |
| Watermelon & cantaloupe | Sow outdoors | Jun 24 – Jul 25 |
| Okra | Sow outdoors | Jun 17 – Jul 10 |
| Peas | Sow outdoors (spring) | Apr 24 – Jun 9 |
| Potatoes | Plant outdoors (spring) | Apr 24 – Jun 24 |
| Onions | Start seeds indoors (spring) | Mar 13 – Apr 9 |
| Onions | Transplant outdoors (spring) | May 11 – Jun 9 |
| Broccoli | Start seeds indoors (spring) | Apr 6 – May 10 |
| Broccoli | Transplant outdoors (spring) | May 11 – Jun 9 |
| Broccoli | Start seeds indoors (fall) | May 25 – Jun 4 |
| Broccoli | Transplant outdoors (fall) | Jun 24 – Jul 5 |
| Cabbage | Start seeds indoors (spring) | Mar 27 – Apr 24 |
| Cabbage | Transplant outdoors (spring) | Apr 24 – May 25 |
| Cabbage | Start seeds indoors (fall) | May 15 – Jun 14 |
| Cabbage | Transplant outdoors (fall) | Jun 14 – Jul 15 |
| Leaf lettuce | Sow outdoors (spring) | Apr 24 – Jul 10 |
| Leaf lettuce | Sow outdoors (fall) | Jun 14 – Jul 31 |
| Spinach | Sow outdoors (spring) | Apr 17 – May 31 |
| Spinach | Sow outdoors (fall) | Jul 1 – Aug 5 |
| Radishes | Sow outdoors (spring) | Apr 24 – Jun 14 |
| Radishes | Sow outdoors (fall) | Jun 14 – Aug 15 |
| Kale | Sow outdoors (spring) | May 11 – May 31 |
| Kale | Sow outdoors (fall) | Jun 7 – Jul 15 |
| Carrots | Sow outdoors (spring) | May 25 – Jul 10 |
| Carrots | Sow outdoors (fall) | May 15 – Jun 30 |
| Garlic | Plant outdoors (fall) | Sep 14 – Oct 15 |
Where these dates come from
ZIP code 49801 is matched to the NOAA station Iron Mtn Ford Ap, MI, 3.6 km away, at 1,149 ft elevation (19 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Iron Mtn Ford Ap, MI (used) | 1,149 ft | May 25 | Sep 24 |
| Iron Mtn-Kingsford Wwtp, MI | 1,071 ft | May 17 | Oct 1 |
| Florence, WI | 1,300 ft | May 24 | Sep 25 |
| Goodman Sanitary Dist, WI | 1,448 ft | May 24 | Sep 30 |
Frost dates near Iron Mountain
- Kingsford, MI 49802 · last May 17, first Oct 1
- Quinnesec, MI 49876 · last May 17, first Oct 1
- Niagara, WI 54151 · last May 17, first Oct 1
- Norway, MI 49870 · last May 17, first Oct 1
- Florence, WI 54121 · last May 24, first Sep 25
- Loretto, MI 49852 · last May 17, first Oct 1
- Vulcan, MI 49892 · last May 17, first Oct 1
- Dunbar, WI 54119 · last May 17, first Oct 1
Frequently asked questions
- When is the last frost in Iron Mountain, MI?
- For ZIP code 49801, the average last spring frost (32°F) is May 25, based on NOAA 1991-2020 climate normals for the Iron Mtn Ford Ap, MI weather station. There is a 1-in-10 chance of a frost after June 6.
- When is the first frost in Iron Mountain, MI?
- The average first fall frost (32°F) is September 24. There is a 1-in-10 chance of frost by September 8, so tender plants are at risk from that point on.
- How long is the growing season in 49801?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 121 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.