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

Planting zone for 50273 — Winterset, IA

ZIP code 50273 (Winterset, Madison County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 30 and the first fall frost October 3.

Where ZIP 50273 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.

Zone5b−15 to −10 °F

Coldest night−26.1 to −23.3 °C

Last frostApr 30

First frostOct 3

2012 zone5a

Was 5a 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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Winterset, IA…

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 Winterset, IA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 30median — 50% chance of a later frost

Safe for tender plantsMay 11only 10% chance of frost after

First fall frostOctober 3median — 10% chance by Sep 20

Growing season157 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 20 and returns around October 15.

From the NOAA station Winterset 1s, IA — 2 miles away, elevation 1,099 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 50273

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 19 – Apr 2

SpinachSow outdoors · Mar 19 – Apr 9

Broccoli, cabbageStart indoors · Feb 19 – Mar 5

Broccoli, cabbageTransplant · Apr 9 – Apr 23

Onion setsPlant outdoors · Apr 2 – Apr 16

PotatoesPlant outdoors · Apr 9 – Apr 23

LettuceSow outdoors · Apr 2 – Apr 16

Carrots, beetsSow outdoors · Apr 9 – Apr 23

TomatoesStart indoors · Mar 5 – Mar 19

TomatoesTransplant · May 7 – May 21

Peppers, eggplantStart indoors · Feb 19 – Mar 5

Peppers, eggplantTransplant · May 14 – May 28

BeansSow outdoors · May 7 – May 21

Sweet cornSow outdoors · May 7 – May 21

Cucumbers, squashSow outdoors · May 7 – May 21

Fall lettuce, spinachSow outdoors · Aug 8 – Aug 22

GarlicPlant cloves · Sep 19 – Oct 24

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 30) and first fall frost (Oct 3) 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 50273 came on Mar 15 — 19 days earlier than the 1991–2020 average (Apr 3).

average
Apr 32026
Mar 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 5b in Iowa

473 plants native to the lower 48 states, recorded in Iowa, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. 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 Winterset, IA.

Soil in Winterset, IA

The soil mapped at the center of ZIP 50273 is Macksburg — silty clay loam, somewhat poorly drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up

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

DrainageSomewhat poorly drainedconsider raised beds

Organic matter5%high

Hydrologic groupC/Dslow when drained; wet otherwise

Farmland classprime farmlandUSDA classification

Map unit: Macksburg silty clay loam, 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 50273; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Winterset, IA

Summer high84 °Faverage high, July

Winter low10 °Faverage low, January

Hot days15days a year at 90 °F or more

Freezing nights145nights a year at 32 °F or less

Growing degree days2,919base 50 °F — the season’s usable heat

Longest day15 h 10 mindaylight on June 21

Shortest day9 h 11 mindaylight on December 21

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

Precipitation34.8 inper year, rain and melted snow

Snowfall31 inper year; 55 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: Winterset 1s, IA (2 mi away); precipitation: Winterset 1s, IA (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

Macksburg, IA · 11 mi

502615b

Van Meter, IA · 12 mi

Saint Charles, IA · 13 mi

Iowa planting zones →

Questions about 50273

What planting zone is ZIP code 50273?

ZIP code 50273 (Winterset, IA) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Winterset, IA?

The median last spring frost (32 °F) near 50273 is April 30; after May 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Winterset 1s station.

When is the first frost in Winterset, IA?

The median first fall frost near 50273 is October 3, giving a median frost-free growing season of 157 days.

When should I plant tomatoes in 50273?

Start tomato seeds indoors around Mar 5 – Mar 19 and set transplants outside around May 7 – May 21, one to three weeks after the median last frost.

How much rain and snow does 50273 get?

About 34.8 inches of precipitation a year and 31 inches of snowfall (NOAA 1991–2020 normals, Winterset 1s station).

How hot do summers get in Winterset, IA?

The average high peaks at 84 °F in July, with about 15 days a year at 90 °F or more.

What kind of soil does 50273 have?

The USDA soil survey maps Macksburg at the center of ZIP 50273: silty clay loam, somewhat poorly drained, pH about 5.9 (moderately acidic).

Did spring come early in Winterset, IA in 2026?

Spring leaf-out near 50273 came on Mar 15 in 2026, 19 days earlier than the 1991–2020 average (Apr 3), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Winterset, IA?

Long-day onions: the longest day near 50273 is 15 h 10 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 50273 change?

Yes. The 2012 USDA map put 50273 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.