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

Planting zone for Janesville, WI

Janesville, WI is in USDA zone 5b across its 4 ZIP codes. The median last spring frost is April 26 and the first fall frost October 15.

Janesville on the zone map

Outlined: its 3 ZIP code areas · 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.

Zone5b−15 to −10 °F
ZIP codes4
Last frostApr 26
First frostOct 15
Growing season170 days

5b 4 ZIPs

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Janesville, 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 Janesville, WI

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 26median — 50% chance of a later frost
Safe for tender plantsMay 11only 10% chance of frost after
First fall frostOctober 15median — 10% chance by Oct 1
Growing season170 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 15 and returns around October 26.

From the NOAA station Afton - Janesville Wwtp, WI, elevation 761 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 Janesville

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 15 – Mar 29
SpinachSow outdoors · Mar 15 – Apr 5
Broccoli, cabbageStart indoors · Feb 15 – Mar 1
Broccoli, cabbageTransplant · Apr 5 – Apr 19
Onion setsPlant outdoors · Mar 29 – Apr 12
PotatoesPlant outdoors · Apr 5 – Apr 19
LettuceSow outdoors · Mar 29 – Apr 12
Carrots, beetsSow outdoors · Apr 5 – Apr 19
TomatoesStart indoors · Mar 1 – Mar 15
TomatoesTransplant · May 3 – May 17
Peppers, eggplantStart indoors · Feb 15 – Mar 1
Peppers, eggplantTransplant · May 10 – May 24
BeansSow outdoors · May 3 – May 17
Sweet cornSow outdoors · May 3 – May 17
Cucumbers, squashSow outdoors · May 3 – May 17
Fall lettuce, spinachSow outdoors · Aug 20 – Sep 3
GarlicPlant cloves · Oct 1 – Nov 5
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 26) and first fall frost (Oct 15) 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 53547 came on Mar 30 — 12 days earlier than the 1991–2020 average (Apr 11).

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 5b in Wisconsin

518 plants native to the lower 48 states, recorded in Wisconsin, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. Each links to its USDA PLANTS profile.

Trees 49

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 93

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 197

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °FAmerican lotus3 ft · blooms mid summer · high shade tolerance · to −36 °FAmerican pokeweed7 ft · blooms mid summer · low shade tolerance · to −33 °F

Grasses 159

American 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 °FBebb's sedge3 ft · blooms late spring · low shade tolerance · to −38 °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 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °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 Janesville, WI.

Soil in Janesville, WI

The soil mapped at the center of ZIP 53547 is Plano — silt loam, well drained.

TextureSilt loama good balance for most vegetables
pH6.7neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter4%moderate
Hydrologic groupBwater soaks in moderately
Farmland classprime farmlandUSDA classification

Map unit: Plano silt loam, gravelly substratum, 0 to 2 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 53547; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Janesville, WI

Summer high83 °Faverage high, July
Winter low12 °Faverage low, January
Hot days13days a year at 90 °F or more
Freezing nights148nights a year at 32 °F or less
Growing degree days2,831base 50 °F — the season’s usable heat
Longest day15 h 20 mindaylight on June 21
Shortest day9 h 02 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation38.9 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 28 °F, low 12 °F 28°12° JanFebruary: average high 32 °F, low 15 °F 32°15° FebMarch: average high 45 °F, low 25 °F 45°25° MarApril: average high 58 °F, low 36 °F 58°36° AprMay: average high 70 °F, low 48 °F 70°48° MayJune: average high 80 °F, low 58 °F 80°58° JunJuly: average high 83 °F, low 62 °F 83°62° JulAugust: average high 82 °F, low 60 °F 82°60° AugSeptember: average high 75 °F, low 51 °F 75°51° SepOctober: average high 62 °F, low 40 °F 62°40° OctNovember: average high 46 °F, low 29 °F 46°29° NovDecember: average high 34 °F, low 18 °F 34°18° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 1.65 in precipitation 1.6 JanFebruary: 1.84 in precipitation 1.8 FebMarch: 2.33 in precipitation 2.3 MarApril: 4.03 in precipitation 4.0 AprMay: 4.42 in precipitation 4.4 MayJune: 5.13 in precipitation 5.1 JunJuly: 3.87 in precipitation 3.9 JulAugust: 4.26 in precipitation 4.3 AugSeptember: 3.88 in precipitation 3.9 SepOctober: 2.89 in precipitation 2.9 OctNovember: 2.58 in precipitation 2.6 NovDecember: 2.06 in precipitation 2.1 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Afton - Janesville Wwtp, WI (7 mi away); precipitation: Milton Wwtp, WI (6 mi away). Daylight is calculated from latitude.

ZIP codes in Janesville

535455b
−15 to −10 °F
535465b
−15 to −10 °F
535475b
−15 to −10 °F
535485b
−15 to −10 °F

Wisconsin planting zones →

Questions about Janesville

What planting zone is Janesville, WI?

Janesville, WI is in USDA hardiness zone 5b on the 2023 map (5b: −15 to −10 °F).

When is the last frost in Janesville, WI?

The median last spring frost is April 26 and the median first fall frost is October 15 (NOAA 1991–2020 normals, Afton - Janesville Wwtp station).

When can I plant a garden in Janesville, WI?

Cool-season crops like peas and spinach go in around Mar 15 – Apr 5; tomatoes, peppers, beans and squash after about May 3, once frost risk has passed.

What kind of onions grow in Janesville, WI?

Long-day onions: the longest day is 15 h 20 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

How much rain and snow does Janesville, WI get?

About 38.9 inches of precipitation a year (NOAA 1991–2020 normals).