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

Planting zone for 48191 — Willis, MI

ZIP code 48191 (Willis, Washtenaw County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 3 and the first fall frost October 10.

Where ZIP 48191 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.

Zone6a−10 to −5 °F

Coldest night−23.3 to −20.6 °C

Last frostMay 3

First frostOct 10

2012 zone5b

Was 5b 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 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Willis, 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 Willis, MI

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 3median — 50% chance of a later frost

Safe for tender plantsMay 25only 10% chance of frost after

First fall frostOctober 10median — 10% chance by Sep 25

Growing season158 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 22 and returns around October 23.

From the NOAA station Milan 4 Ese, MI — 4 miles away, elevation 669 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 48191

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 22 – Apr 5

SpinachSow outdoors · Mar 22 – Apr 12

Broccoli, cabbageStart indoors · Feb 22 – Mar 8

Broccoli, cabbageTransplant · Apr 12 – Apr 26

Onion setsPlant outdoors · Apr 5 – Apr 19

PotatoesPlant outdoors · Apr 12 – Apr 26

LettuceSow outdoors · Apr 5 – Apr 19

Carrots, beetsSow outdoors · Apr 12 – Apr 26

TomatoesStart indoors · Mar 8 – Mar 22

TomatoesTransplant · May 10 – May 24

Peppers, eggplantStart indoors · Feb 22 – Mar 8

Peppers, eggplantTransplant · May 17 – May 31

BeansSow outdoors · May 10 – May 24

Sweet cornSow outdoors · May 10 – May 24

Cucumbers, squashSow outdoors · May 10 – May 24

Fall lettuce, spinachSow outdoors · Aug 15 – Aug 29

GarlicPlant cloves · Sep 26 – Oct 31

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 3) and first fall frost (Oct 10) 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 48191 came on Apr 2 — 5 days earlier than the 1991–2020 average (Apr 7).

average
Apr 72026
Apr 2

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 6a in Michigan

580 plants native to the lower 48 states, recorded in Michigan, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. 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 Willis, MI.

Soil in Willis, MI

The soil mapped at the center of ZIP 48191 is Lamson — fine sandy loam, poorly drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding

pH7.0neutral; most vegetables like 6.0–7.0

DrainagePoorly drainedconsider raised beds

Organic matter6.5%high

Hydrologic groupA/Ddrains fast once dried out; wet otherwise

Farmland classPrime farmland if drainedUSDA classification

Map unit: Lamson-Colwood complex.

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 48191; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Willis, MI

Summer high83 °Faverage high, July

Winter low16 °Faverage low, January

Hot days11days a year at 90 °F or more

Freezing nights143nights a year at 32 °F or less

Growing degree days2,790base 50 °F — the season’s usable heat

Longest day15 h 15 mindaylight on June 21

Shortest day9 h 06 mindaylight on December 21

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

Precipitation35.9 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Milan 4 Ese, MI (4 mi away); precipitation: Milan Wwtp, MI (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

481906a

Whittaker, MI · 2 mi

481116a

Belleville, MI · 6 mi

Belleville, MI · 7 mi

481646b

New Boston, MI · 9 mi

481106a

Azalia, MI · 9 mi

Michigan planting zones →

Questions about 48191

What planting zone is ZIP code 48191?

ZIP code 48191 (Willis, MI) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Willis, MI?

The median last spring frost (32 °F) near 48191 is May 3; after May 25 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Milan 4 Ese station.

When is the first frost in Willis, MI?

The median first fall frost near 48191 is October 10, giving a median frost-free growing season of 158 days.

When should I plant tomatoes in 48191?

Start tomato seeds indoors around Mar 8 – Mar 22 and set transplants outside around May 10 – May 24, one to three weeks after the median last frost.

How much rain and snow does 48191 get?

About 35.9 inches of precipitation a year (NOAA 1991–2020 normals, Milan Wwtp station).

How hot do summers get in Willis, MI?

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 48191 have?

The USDA soil survey maps Lamson at the center of ZIP 48191: fine sandy loam, poorly drained, pH about 7.0 (neutral).

Did spring come early in Willis, MI in 2026?

Spring leaf-out near 48191 came on Apr 2 in 2026, 5 days earlier than the 1991–2020 average (Apr 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Willis, MI?

Long-day onions: the longest day near 48191 is 15 h 15 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 48191 change?

Yes. The 2012 USDA map put 48191 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.