Frost Dates for Iron Mountain, MI 49801
Last spring frost May 27 · First fall frost September 20 · 116 frost-free days · USDA Zone 4b
Frost probability for 49801
| Frost | 10% | 50% | 90% |
|---|---|---|---|
| Spring (last frost) | June 10 | May 27 | May 12 |
| Fall (first frost) | September 9 | September 20 | October 2 |
Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (15.7 km away); the 50% date is the median year.
Month by month in Iron Mountain
| Month | What to do |
|---|---|
| January | Plan your garden layout and order seeds. Research varieties suited to your frost dates. |
| February | Start the slowest-growing crops indoors: onions, leeks, and celery (10–12 weeks before last frost). |
| March | Start peppers and eggplant indoors 8–10 weeks before your last frost (around May 27). Start tomatoes about two weeks later, 6–8 weeks before last frost. |
| April | Start herbs, basil, and squash indoors (4–6 weeks before frost). Direct sow peas, spinach, and lettuce if soil is workable. |
| May | Last frost around May 27. Transplant cold-hardy crops (broccoli, kale, cabbage). Harden off tomato and pepper seedlings. |
| June | Frost has passed. Transplant tomatoes, peppers, and basil outdoors. Direct sow beans, cucumbers, squash, and zucchini. |
| July | Succession plant lettuce and greens. Keep beds weeded and watered consistently. |
| August | First fall frost approaching (around September 20). Transplant fall brassicas. Sow spinach, arugula, and radishes. |
| September | First frost around September 20. Harvest tomatoes and peppers before frost. Cover cold-hardy crops with row covers to extend the season. |
| October | Harvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year. |
| November | Clean up spent plants. Add compost to beds. Rest, review, and plan next year's garden. |
| December | Clean up spent plants. Add compost to beds. Rest, review, and plan next year's garden. |
What grows in a 116-day season
Frequently Asked Questions
What is the last frost date for Iron Mountain, MI (ZIP 49801)?
The median last spring frost date for Iron Mountain, MI (ZIP code 49801) is around May 27. This is the 50th-percentile date — meaning half of all years see frost end before this date. Use the 10% and 90% dates to understand the full range of risk in your area.
What is the first fall frost date in Iron Mountain, MI?
The median first fall frost date for Iron Mountain, MI is around September 20. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses.
How long is the growing season in Iron Mountain, MI?
The frost-free growing season in Iron Mountain is about 116 days. This window — from your last spring frost to your first fall frost — is when warm-season vegetables thrive. Cold-hardy crops like kale, spinach, and peas can extend your season by weeks on either side.
What USDA hardiness zone is Iron Mountain, MI?
Based on frost date patterns, Iron Mountain falls approximately in 4b. USDA hardiness zones are determined by average annual minimum winter temperatures and guide both plant selection and planting timing for your location.
When should I start tomatoes indoors in Iron Mountain, MI?
Start tomato seeds indoors 6–8 weeks before your last frost date (around May 27). For Iron Mountain, that's roughly April 1 to April 15. Transplant outdoors 1–2 weeks after your last frost.
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