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

Planting zone for 54421 — Colby, WI

ZIP code 54421 (Colby, Clark County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 13 and the first fall frost September 26.

Where ZIP 54421 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 13

First frostSep 26

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 Colby, WI…

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 Colby, WI

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 13median — 50% chance of a later frost

Safe for tender plantsMay 29only 10% chance of frost after

First fall frostSeptember 26median — 10% chance by Sep 12

Growing season136 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 2 and returns around October 5.

From the NOAA station Owen 1e, WI — 13 miles away, elevation 1,237 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 54421

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 1 – Apr 15

SpinachSow outdoors · Apr 1 – Apr 22

Broccoli, cabbageStart indoors · Mar 4 – Mar 18

Broccoli, cabbageTransplant · Apr 22 – May 6

Onion setsPlant outdoors · Apr 15 – Apr 29

PotatoesPlant outdoors · Apr 22 – May 6

LettuceSow outdoors · Apr 15 – Apr 29

Carrots, beetsSow outdoors · Apr 22 – May 6

TomatoesStart indoors · Mar 18 – Apr 1

TomatoesTransplant · May 20 – Jun 3

Peppers, eggplantStart indoors · Mar 4 – Mar 18

Peppers, eggplantTransplant · May 27 – Jun 10

BeansSow outdoors · May 20 – Jun 3

Sweet cornSow outdoors · May 20 – Jun 3

Cucumbers, squashSow outdoors · May 20 – Jun 3

Fall lettuce, spinachSow outdoors · Aug 1 – Aug 15

GarlicPlant cloves · Sep 12 – Oct 17

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 13) and first fall frost (Sep 26) 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 54421 came on Apr 15 — 5 days earlier than the 1991–2020 average (Apr 20).

average
Apr 202026
Apr 15

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 Wisconsin

486 plants native to the lower 48 states, recorded in Wisconsin, 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 Colby, WI.

Soil in Colby, WI

The soil mapped at the center of ZIP 54421 is Withee — silt loam, somewhat poorly drained.

TextureSilt loama good balance for most vegetables

pH5.9moderately acidic; most vegetables like 6.0–7.0

DrainageSomewhat poorly drainedconsider raised beds

Organic matter3.5%moderate

Hydrologic groupC/Dslow when drained; wet otherwise

Farmland classPrime farmland if drainedUSDA classification

Map unit: Withee silt loam, 0 to 3 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 54421; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Colby, WI

Summer high79 °Faverage high, July

Winter low2 °Faverage low, January

Hot days3days a year at 90 °F or more

Freezing nights173nights a year at 32 °F or less

Growing degree days2,010base 50 °F — the season’s usable heat

Longest day15 h 36 mindaylight on June 21

Shortest day8 h 47 mindaylight on December 21

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

Precipitation30.9 inper year, rain and melted snow

Snowfall45 inper year

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Owen 1e, WI (13 mi away); precipitation: Stratford 1 Nw, WI (11 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 4b.

544884b

Unity, WI · 5 mi

544054b

Abbotsford, WI · 5 mi

544254b

Dorchester, WI · 8 mi

Stetsonville, WI · 11 mi

544844b

Stratford, WI · 12 mi

544604b

Owen, WI · 13 mi

Wisconsin planting zones →

Questions about 54421

What planting zone is ZIP code 54421?

ZIP code 54421 (Colby, WI) 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 Colby, WI?

The median last spring frost (32 °F) near 54421 is May 13; after May 29 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Owen 1e station.

When is the first frost in Colby, WI?

The median first fall frost near 54421 is September 26, giving a median frost-free growing season of 136 days.

When should I plant tomatoes in 54421?

Start tomato seeds indoors around Mar 18 – Apr 1 and set transplants outside around May 20 – Jun 3, one to three weeks after the median last frost.

How much rain and snow does 54421 get?

About 30.9 inches of precipitation a year and 45 inches of snowfall (NOAA 1991–2020 normals, Stratford 1 Nw station).

How hot do summers get in Colby, WI?

The average high peaks at 79 °F in July, with about 3 days a year at 90 °F or more.

What kind of soil does 54421 have?

The USDA soil survey maps Withee at the center of ZIP 54421: silt loam, somewhat poorly drained, pH about 5.9 (moderately acidic).

Did spring come early in Colby, WI in 2026?

Spring leaf-out near 54421 came on Apr 15 in 2026, 5 days earlier than the 1991–2020 average (Apr 20), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Colby, WI?

Long-day onions: the longest day near 54421 is 15 h 36 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 54421 change?

Yes. The 2012 USDA map put 54421 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.