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

Planting zone for 54840 — Grantsburg, WI

ZIP code 54840 (Grantsburg, Burnett County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F. The median last spring frost is May 11 and the first fall frost October 1.

Where ZIP 54840 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.

Zone4a−30 to −25 °F
Coldest night−34.4 to −31.7 °C
Last frostMay 11
First frostOct 1
2012 zone4a

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 4a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Grantsburg, 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 Grantsburg, WI

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 11median — 50% chance of a later frost
Safe for tender plantsMay 28only 10% chance of frost after
First fall frostOctober 1median — 10% chance by Sep 16
Growing season141 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 30 and returns around October 11.

From the NOAA station Grantsburg, WI — within 1 mile, elevation 991 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 54840

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 30 – Apr 13
SpinachSow outdoors · Mar 30 – Apr 20
Broccoli, cabbageStart indoors · Mar 2 – Mar 16
Broccoli, cabbageTransplant · Apr 20 – May 4
Onion setsPlant outdoors · Apr 13 – Apr 27
PotatoesPlant outdoors · Apr 20 – May 4
LettuceSow outdoors · Apr 13 – Apr 27
Carrots, beetsSow outdoors · Apr 20 – May 4
TomatoesStart indoors · Mar 16 – Mar 30
TomatoesTransplant · May 18 – Jun 1
Peppers, eggplantStart indoors · Mar 2 – Mar 16
Peppers, eggplantTransplant · May 25 – Jun 8
BeansSow outdoors · May 18 – Jun 1
Sweet cornSow outdoors · May 18 – Jun 1
Cucumbers, squashSow outdoors · May 18 – Jun 1
Fall lettuce, spinachSow outdoors · Aug 6 – Aug 20
GarlicPlant cloves · Sep 17 – Oct 22
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 11) and first fall frost (Oct 1) 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 54840 came on Apr 16 — 3 days earlier than the 1991–2020 average (Apr 19).

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).

Soil in Grantsburg, WI

The soil mapped at the center of ZIP 54840 is Branstad — loam, moderately well drained.

TextureLoama good balance for most vegetables
pH5.5moderately acidic; most vegetables like 6.0–7.0
DrainageModerately well drainednatural drainage class
Organic matter3%moderate
Hydrologic groupCwater soaks in slowly
Farmland classprime farmlandUSDA classification

Map unit: Branstad loam, 2 to 6 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 54840; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Grantsburg, WI

Summer high82 °Faverage high, July
Winter low1 °Faverage low, January
Hot days9days a year at 90 °F or more
Freezing nights177nights a year at 32 °F or less
Growing degree days2,339base 50 °F — the season’s usable heat
Longest day15 h 43 mindaylight on June 21
Shortest day8 h 40 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation33.8 inper year, rain and melted snow
Snowfall52 inper year; 113 days with snow on the ground

Average high and low, by month

−10°0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 22 °F, low 1 °F 22°1° JanFebruary: average high 28 °F, low 5 °F 28°5° FebMarch: average high 41 °F, low 18 °F 41°18° MarApril: average high 56 °F, low 31 °F 56°31° AprMay: average high 69 °F, low 44 °F 69°44° MayJune: average high 78 °F, low 53 °F 78°53° JunJuly: average high 82 °F, low 58 °F 82°58° JulAugust: average high 80 °F, low 56 °F 80°56° AugSeptember: average high 72 °F, low 47 °F 72°47° SepOctober: average high 58 °F, low 35 °F 58°35° OctNovember: average high 41 °F, low 22 °F 41°22° NovDecember: average high 27 °F, low 10 °F 27°10° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″January: 0.86 in precipitation, 10.8 in snowfall 0.9❄11 JanFebruary: 0.90 in precipitation, 8.9 in snowfall 0.9❄9 FebMarch: 1.58 in precipitation, 8.4 in snowfall 1.6❄8 MarApril: 2.85 in precipitation, 3.5 in snowfall 2.9❄4 AprMay: 4.06 in precipitation, 0.1 in snowfall 4.1 MayJune: 4.45 in precipitation 4.5 JunJuly: 4.60 in precipitation 4.6 JulAugust: 4.45 in precipitation 4.5 AugSeptember: 3.67 in precipitation 3.7 SepOctober: 3.17 in precipitation, 0.5 in snowfall 3.2❄1 OctNovember: 1.81 in precipitation, 8.1 in snowfall 1.8❄8 NovDecember: 1.37 in precipitation, 11.9 in snowfall 1.4❄12 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Grantsburg, WI (within 1 mile); precipitation: Grantsburg, WI (within 1 mile). 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.

540064a
Cushing, WI · 11 mi
550634a
Pine City, MN · 12 mi
550694b
Rush City, MN · 14 mi
548724b
Siren, WI · 15 mi
548534b
Luck, WI · 17 mi
548374b
Frederic, WI · 17 mi
540244a
Saint Croix Falls, WI · 17 mi
550324b
Harris, MN · 18 mi

Wisconsin planting zones →

Questions about 54840

What planting zone is ZIP code 54840?

ZIP code 54840 (Grantsburg, WI) is in USDA hardiness zone 4a on the 2023 map: the coldest night of an average winter reaches −30 to −25 °F (−34.4 to −31.7 °C).

When is the last frost in Grantsburg, WI?

The median last spring frost (32 °F) near 54840 is May 11; after May 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Grantsburg station.

When is the first frost in Grantsburg, WI?

The median first fall frost near 54840 is October 1, giving a median frost-free growing season of 141 days.

When should I plant tomatoes in 54840?

Start tomato seeds indoors around Mar 16 – Mar 30 and set transplants outside around May 18 – Jun 1, one to three weeks after the median last frost.

How much rain and snow does 54840 get?

About 33.8 inches of precipitation a year and 52 inches of snowfall (NOAA 1991–2020 normals, Grantsburg station).

How hot do summers get in Grantsburg, WI?

The average high peaks at 82 °F in July, with about 9 days a year at 90 °F or more.

What kind of soil does 54840 have?

The USDA soil survey maps Branstad at the center of ZIP 54840: loam, moderately well drained, pH about 5.5 (moderately acidic).

Did spring come early in Grantsburg, WI in 2026?

Spring leaf-out near 54840 came on Apr 16 in 2026, 3 days earlier than the 1991–2020 average (Apr 19), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Grantsburg, WI?

Long-day onions: the longest day near 54840 is 15 h 43 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).