Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 49938 — Ironwood, MI

ZIP code 49938 (Ironwood, Gogebic County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 19 and the first fall frost September 28.

Where ZIP 49938 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 19

First frostSep 28

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 Ironwood, 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 Ironwood, MI

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostMay 19median — 50% chance of a later frost

Safe for tender plantsJune 3only 10% chance of frost after

First fall frostSeptember 28median — 10% chance by Sep 12

Growing season130 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 5 and returns around October 9.

From the NOAA station Ironwood #2, MI — 4 miles away, elevation 1,519 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 49938

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 7 – Apr 21

SpinachSow outdoors · Apr 7 – Apr 28

Broccoli, cabbageStart indoors · Mar 10 – Mar 24

Broccoli, cabbageTransplant · Apr 28 – May 12

Onion setsPlant outdoors · Apr 21 – May 5

PotatoesPlant outdoors · Apr 28 – May 12

LettuceSow outdoors · Apr 21 – May 5

Carrots, beetsSow outdoors · Apr 28 – May 12

TomatoesStart indoors · Mar 24 – Apr 7

TomatoesTransplant · May 26 – Jun 9

Peppers, eggplantStart indoors · Mar 10 – Mar 24

Peppers, eggplantTransplant · Jun 2 – Jun 16

BeansSow outdoors · May 26 – Jun 9

Sweet cornSow outdoors · May 26 – Jun 9

Cucumbers, squashSow outdoors · May 26 – Jun 9

Fall lettuce, spinachSow outdoors · Aug 3 – Aug 17

GarlicPlant cloves · Sep 14 – Oct 19

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 19) and first fall frost (Sep 28) 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 49938 came on Apr 27 — about the same time as the 1991–2020 average (Apr 26).

average
Apr 262026
Apr 27

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.

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 Ironwood, MI.

Soil in Ironwood, MI

The soil mapped at the center of ZIP 49938 is Wakefield — slightly decomposed plant material, moderately well drained.

TextureSlightly decomposed plant materialtop layer

pH4.1strongly acidic; most vegetables like 6.0–7.0

DrainageModerately well drainednatural drainage class

Organic matter75%high

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Wakefield loam, 1 to 6 percent slopes, stony.

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 49938; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Ironwood, MI

Summer high77 °Faverage high, July

Winter low2 °Faverage low, January

Hot days1days a year at 90 °F or more

Freezing nights203nights a year at 32 °F or less

Growing degree days1,640base 50 °F — the season’s usable heat

Longest day15 h 50 mindaylight on June 21

Shortest day8 h 34 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation37.4 inper year, rain and melted snow

Snowfall186 inper year

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Ironwood #2, MI (4 mi away); precipitation: Ironwood, MI (5 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Wakefield, MI · 12 mi

Iron Belt, WI · 16 mi

545594b

Saxon, WI · 17 mi

Michigan planting zones →

Questions about 49938

What planting zone is ZIP code 49938?

ZIP code 49938 (Ironwood, 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 Ironwood, MI?

The median last spring frost (32 °F) near 49938 is May 19; after June 3 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Ironwood #2 station.

When is the first frost in Ironwood, MI?

The median first fall frost near 49938 is September 28, giving a median frost-free growing season of 130 days.

When should I plant tomatoes in 49938?

Start tomato seeds indoors around Mar 24 – Apr 7 and set transplants outside around May 26 – Jun 9, one to three weeks after the median last frost.

How much rain and snow does 49938 get?

About 37.4 inches of precipitation a year and 186 inches of snowfall (NOAA 1991–2020 normals, Ironwood station).

How hot do summers get in Ironwood, MI?

The average high peaks at 77 °F in July, with about 1 days a year at 90 °F or more.

What kind of soil does 49938 have?

The USDA soil survey maps Wakefield at the center of ZIP 49938: slightly decomposed plant material, moderately well drained, pH about 4.1 (strongly acidic).

Did spring come early in Ironwood, MI in 2026?

Spring leaf-out near 49938 came on Apr 27 in 2026, about the same as the 1991–2020 average (Apr 26), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Ironwood, MI?

Long-day onions: the longest day near 49938 is 15 h 50 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 49938 change?

Yes. The 2012 USDA map put 49938 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.