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

Planting zone for 53561 — Merrimac, WI

ZIP code 53561 (Merrimac, Sauk County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 5 and the first fall frost October 5.

Where ZIP 53561 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.

Zone5a−20 to −15 °F

Coldest night−28.9 to −26.1 °C

Last frostMay 5

First frostOct 5

2012 zone5a

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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Merrimac, 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 Merrimac, WI

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 5median — 50% chance of a later frost

Safe for tender plantsMay 21only 10% chance of frost after

First fall frostOctober 5median — 10% chance by Sep 22

Growing season152 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 24 and returns around October 17.

From the NOAA station Baraboo, WI — 6 miles away, elevation 824 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 53561

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 24 – Apr 7

SpinachSow outdoors · Mar 24 – Apr 14

Broccoli, cabbageStart indoors · Feb 24 – Mar 10

Broccoli, cabbageTransplant · Apr 14 – Apr 28

Onion setsPlant outdoors · Apr 7 – Apr 21

PotatoesPlant outdoors · Apr 14 – Apr 28

LettuceSow outdoors · Apr 7 – Apr 21

Carrots, beetsSow outdoors · Apr 14 – Apr 28

TomatoesStart indoors · Mar 10 – Mar 24

TomatoesTransplant · May 12 – May 26

Peppers, eggplantStart indoors · Feb 24 – Mar 10

Peppers, eggplantTransplant · May 19 – Jun 2

BeansSow outdoors · May 12 – May 26

Sweet cornSow outdoors · May 12 – May 26

Cucumbers, squashSow outdoors · May 12 – May 26

Fall lettuce, spinachSow outdoors · Aug 10 – Aug 24

GarlicPlant cloves · Sep 21 – Oct 26

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 5) and first fall frost (Oct 5) 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 53561 came on Mar 30 — 13 days earlier than the 1991–2020 average (Apr 12).

average
Apr 122026
Mar 30

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 5a in Wisconsin

510 plants native to the lower 48 states, recorded in Wisconsin, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. 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 Merrimac, WI.

Soil in Merrimac, WI

The soil mapped at the center of ZIP 53561 is Adrian — muck, very poorly drained.

TextureMucktop layer

DrainageVery poorly drainedconsider raised beds

Organic matter70%high

Hydrologic groupB/Dmoderate when drained; wet otherwise

Farmland classNot prime farmlandUSDA classification

Map unit: Adrian muck, 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 53561; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Merrimac, WI

Summer high83 °Faverage high, July

Winter low10 °Faverage low, January

Hot days11days a year at 90 °F or more

Freezing nights169nights a year at 32 °F or less

Growing degree days2,625base 50 °F — the season’s usable heat

Longest day15 h 25 mindaylight on June 21

Shortest day8 h 57 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

Snowfall43 inper year; 75 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: Baraboo, WI (6 mi away); precipitation: Baraboo, WI (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

Prairie Du Sac, WI · 8 mi

539515a

North Freedom, WI · 11 mi

Sauk City, WI · 13 mi

539015a

Portage, WI · 14 mi

Wisconsin planting zones →

Questions about 53561

What planting zone is ZIP code 53561?

ZIP code 53561 (Merrimac, WI) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Merrimac, WI?

The median last spring frost (32 °F) near 53561 is May 5; after May 21 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Baraboo station.

When is the first frost in Merrimac, WI?

The median first fall frost near 53561 is October 5, giving a median frost-free growing season of 152 days.

When should I plant tomatoes in 53561?

Start tomato seeds indoors around Mar 10 – Mar 24 and set transplants outside around May 12 – May 26, one to three weeks after the median last frost.

How much rain and snow does 53561 get?

About 38.9 inches of precipitation a year and 43 inches of snowfall (NOAA 1991–2020 normals, Baraboo station).

How hot do summers get in Merrimac, WI?

The average high peaks at 83 °F in July, with about 11 days a year at 90 °F or more.

What kind of soil does 53561 have?

The USDA soil survey maps Adrian at the center of ZIP 53561: muck, very poorly drained.

Did spring come early in Merrimac, WI in 2026?

Spring leaf-out near 53561 came on Mar 30 in 2026, 13 days earlier than the 1991–2020 average (Apr 12), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Merrimac, WI?

Long-day onions: the longest day near 53561 is 15 h 25 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).