Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 49801 — Iron Mountain, MI

ZIP code 49801 (Iron Mountain, Dickinson County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 25 and the first fall frost September 24.

Where ZIP 49801 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone4b−25 to −20 °F
Coldest night−31.7 to −28.9 °C
Last frostMay 25
First frostSep 24
2012 zone4a

Was 4a on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Iron Mountain, MI…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Iron Mountain, MI

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 25median — 50% chance of a later frost
Safe for tender plantsJune 6only 10% chance of frost after
First fall frostSeptember 24median — 10% chance by Sep 8
Growing season121 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 11 and returns around October 5.

From the NOAA station Iron Mtn Ford Airport, MI — 9 miles away, elevation 1,148 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 49801

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 13 – Apr 27
SpinachSow outdoors · Apr 13 – May 4
Broccoli, cabbageStart indoors · Mar 16 – Mar 30
Broccoli, cabbageTransplant · May 4 – May 18
Onion setsPlant outdoors · Apr 27 – May 11
PotatoesPlant outdoors · May 4 – May 18
LettuceSow outdoors · Apr 27 – May 11
Carrots, beetsSow outdoors · May 4 – May 18
TomatoesStart indoors · Mar 30 – Apr 13
TomatoesTransplant · Jun 1 – Jun 15
Peppers, eggplantStart indoors · Mar 16 – Mar 30
Peppers, eggplantTransplant · Jun 8 – Jun 22
BeansSow outdoors · Jun 1 – Jun 15
Sweet cornSow outdoors · Jun 1 – Jun 15
Cucumbers, squashSow outdoors · Jun 1 – Jun 15
Fall lettuce, spinachSow outdoors · Jul 30 – Aug 13
GarlicPlant cloves · Sep 10 – Oct 15
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 25) and first fall frost (Sep 24) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 49801 came on Apr 23 — about the same time as the 1991–2020 average (Apr 25).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 4b in Michigan

514 plants native to the lower 48 states, recorded in Michigan, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. Each links to its USDA PLANTS profile.

Trees 51

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican beech80 ft · blooms mid spring · low shade tolerance · to −44 °FAmerican chestnut115 ft · blooms early summer · high shade tolerance · to −33 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Farborvitae50 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 97

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falternateleaf dogwood25 ft · blooms mid spring · low shade tolerance · to −47 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °FAmerican hornbeam30 ft · blooms mid spring · low shade tolerance · to −34 °F

Wildflowers & perennials 190

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine sweetvetch2 ft · blooms early summer · high shade tolerance · to −62 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican lotus3 ft · blooms mid summer · high shade tolerance · to −36 °F

Grasses 157

alpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °FAmerican beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °Fbeaked sedge4 ft · blooms late spring · low shade tolerance · to −38 °Fbeaked spikerush3 ft · blooms late spring · high shade tolerance · to −28 °F

Vines 5

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Ftrumpet honeysuckle16 ft · blooms late summer · low shade tolerance · to −33 °FVirginia creeper1 ft · blooms late spring · medium shade tolerance · to −28 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Iron Mountain, MI.

Soil in Iron Mountain, MI

The soil mapped at the center of ZIP 49801 is Emmet — highly decomposed plant material, well drained.

TextureHighly decomposed plant materialtop layer
pH6.0slightly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter75%high
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Emmet-Rock outcrop complex, 6 to 18 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 49801; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Iron Mountain, MI

Summer high80 °Faverage high, July
Winter low6 °Faverage low, January
Hot days6days a year at 90 °F or more
Freezing nights187nights a year at 32 °F or less
Growing degree days1,882base 50 °F — the season’s usable heat
Longest day15 h 45 mindaylight on June 21
Shortest day8 h 39 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation31.9 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 24 °F, low 6 °F 24°6° JanFebruary: average high 27 °F, low 7 °F 27°7° FebMarch: average high 38 °F, low 17 °F 38°17° MarApril: average high 52 °F, low 27 °F 52°27° AprMay: average high 66 °F, low 40 °F 66°40° MayJune: average high 76 °F, low 50 °F 76°50° JunJuly: average high 80 °F, low 54 °F 80°54° JulAugust: average high 78 °F, low 53 °F 78°53° AugSeptember: average high 70 °F, low 45 °F 70°45° SepOctober: average high 55 °F, low 34 °F 55°34° OctNovember: average high 40 °F, low 24 °F 40°24° NovDecember: average high 29 °F, low 13 °F 29°13° Dec

Precipitation by month inches

0″1″2″3″4″January: 1.35 in precipitation 1.4 JanFebruary: 1.20 in precipitation 1.2 FebMarch: 1.60 in precipitation 1.6 MarApril: 3.12 in precipitation 3.1 AprMay: 3.29 in precipitation 3.3 MayJune: 3.98 in precipitation 4.0 JunJuly: 3.74 in precipitation 3.7 JulAugust: 3.25 in precipitation 3.3 AugSeptember: 3.66 in precipitation 3.7 SepOctober: 3.34 in precipitation 3.3 OctNovember: 1.78 in precipitation 1.8 NovDecember: 1.55 in precipitation 1.6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Iron Mtn Ford Airport, MI (9 mi away); precipitation: Florence 5.6 Ese, WI (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

2 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

498704b
Norway, MI · 8 mi
498764b
Quinnesec, MI · 9 mi
498024b
Kingsford, MI · 9 mi
498814b
Sagola, MI · 10 mi
498525a
Loretto, MI · 14 mi
541514b
Niagara, WI · 14 mi
498925a
Vulcan, MI · 15 mi
541214b
Florence, WI · 16 mi

Michigan planting zones →

Questions about 49801

What planting zone is ZIP code 49801?

ZIP code 49801 (Iron Mountain, MI) is in USDA hardiness zone 4b on the 2023 map: the coldest night of an average winter reaches −25 to −20 °F (−31.7 to −28.9 °C).

When is the last frost in Iron Mountain, MI?

The median last spring frost (32 °F) near 49801 is May 25; after June 6 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Iron Mtn Ford Airport station.

When is the first frost in Iron Mountain, MI?

The median first fall frost near 49801 is September 24, giving a median frost-free growing season of 121 days.

When should I plant tomatoes in 49801?

Start tomato seeds indoors around Mar 30 – Apr 13 and set transplants outside around Jun 1 – Jun 15, one to three weeks after the median last frost.

How much rain and snow does 49801 get?

About 31.9 inches of precipitation a year (NOAA 1991–2020 normals, Florence 5.6 Ese station).

How hot do summers get in Iron Mountain, MI?

The average high peaks at 80 °F in July, with about 6 days a year at 90 °F or more.

What kind of soil does 49801 have?

The USDA soil survey maps Emmet at the center of ZIP 49801: highly decomposed plant material, well drained, pH about 6.0 (slightly acidic).

Did spring come early in Iron Mountain, MI in 2026?

Spring leaf-out near 49801 came on Apr 23 in 2026, about the same as the 1991–2020 average (Apr 25), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Iron Mountain, MI?

Long-day onions: the longest day near 49801 is 15 h 45 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 49801 change?

Yes. The 2012 USDA map put 49801 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.