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

Planting zone for 49902 — Alpha, MI

ZIP code 49902 (Alpha, Iron County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 24 and the first fall frost September 25.

Where ZIP 49902 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 24

First frostSep 25

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 Alpha, 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 Alpha, MI

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 24median — 50% chance of a later frost

Safe for tender plantsJune 8only 10% chance of frost after

First fall frostSeptember 25median — 10% chance by Sep 7

Growing season121 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 11 and returns around October 6.

From the NOAA station Florence, WI — 10 miles away, elevation 1,299 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 49902

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 12 – Apr 26

SpinachSow outdoors · Apr 12 – May 3

Broccoli, cabbageStart indoors · Mar 15 – Mar 29

Broccoli, cabbageTransplant · May 3 – May 17

Onion setsPlant outdoors · Apr 26 – May 10

PotatoesPlant outdoors · May 3 – May 17

LettuceSow outdoors · Apr 26 – May 10

Carrots, beetsSow outdoors · May 3 – May 17

TomatoesStart indoors · Mar 29 – Apr 12

TomatoesTransplant · May 31 – Jun 14

Peppers, eggplantStart indoors · Mar 15 – Mar 29

Peppers, eggplantTransplant · Jun 7 – Jun 21

BeansSow outdoors · May 31 – Jun 14

Sweet cornSow outdoors · May 31 – Jun 14

Cucumbers, squashSow outdoors · May 31 – Jun 14

Fall lettuce, spinachSow outdoors · Jul 31 – Aug 14

GarlicPlant cloves · Sep 11 – Oct 16

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 24) and first fall frost (Sep 25) 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 49902 came on Apr 23 — 5 days earlier than the 1991–2020 average (Apr 28).

average
Apr 282026
Apr 23

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 Alpha, MI.

Soil in Alpha, MI

The soil mapped at the center of ZIP 49902 is Peavy — silt loam, well drained.

TextureSilt loama good balance for most vegetables

pH5.8moderately acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter5%high

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Peavy silt loam, 6 to 18 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 49902; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Alpha, MI

Summer high78 °Faverage high, July

Winter low3 °Faverage low, January

Hot days3days a year at 90 °F or more

Freezing nights190nights a year at 32 °F or less

Growing degree days1,717base 50 °F — the season’s usable heat

Longest day15 h 46 mindaylight on June 21

Shortest day8 h 38 mindaylight on December 21

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

Precipitation30.4 inper year, rain and melted snow

Snowfall66 inper year; 124 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Florence, WI (10 mi away); precipitation: Florence, WI (10 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

499204a

Crystal Falls, MI · 7 mi

Stambaugh, MI · 12 mi

Iron Mountain, MI · 19 mi

541204b

Fence, WI · 19 mi

Michigan planting zones →

Questions about 49902

What planting zone is ZIP code 49902?

ZIP code 49902 (Alpha, 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 Alpha, MI?

The median last spring frost (32 °F) near 49902 is May 24; after June 8 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Florence station.

When is the first frost in Alpha, MI?

The median first fall frost near 49902 is September 25, giving a median frost-free growing season of 121 days.

When should I plant tomatoes in 49902?

Start tomato seeds indoors around Mar 29 – Apr 12 and set transplants outside around May 31 – Jun 14, one to three weeks after the median last frost.

How much rain and snow does 49902 get?

About 30.4 inches of precipitation a year and 66 inches of snowfall (NOAA 1991–2020 normals, Florence station).

How hot do summers get in Alpha, MI?

The average high peaks at 78 °F in July, with about 3 days a year at 90 °F or more.

What kind of soil does 49902 have?

The USDA soil survey maps Peavy at the center of ZIP 49902: silt loam, well drained, pH about 5.8 (moderately acidic).

Did spring come early in Alpha, MI in 2026?

Spring leaf-out near 49902 came on Apr 23 in 2026, 5 days earlier than the 1991–2020 average (Apr 28), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Alpha, MI?

Long-day onions: the longest day near 49902 is 15 h 46 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 49902 change?

Yes. The 2012 USDA map put 49902 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.