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

Planting zone for 51551 — Malvern, IA

ZIP code 51551 (Malvern, Mills County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 23 and the first fall frost October 11.

Where ZIP 51551 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 23

First frostOct 11

2012 zone5b

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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Malvern, 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 Malvern, IA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 23median — 50% chance of a later frost

Safe for tender plantsMay 6only 10% chance of frost after

First fall frostOctober 11median — 10% chance by Sep 27

Growing season170 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 12 and returns around October 21.

From the NOAA station Glenwood 3sw, IA — 10 miles away, elevation 981 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 51551

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 12 – Mar 26

SpinachSow outdoors · Mar 12 – Apr 2

Broccoli, cabbageStart indoors · Feb 12 – Feb 26

Broccoli, cabbageTransplant · Apr 2 – Apr 16

Onion setsPlant outdoors · Mar 26 – Apr 9

PotatoesPlant outdoors · Apr 2 – Apr 16

LettuceSow outdoors · Mar 26 – Apr 9

Carrots, beetsSow outdoors · Apr 2 – Apr 16

TomatoesStart indoors · Feb 26 – Mar 12

TomatoesTransplant · Apr 30 – May 14

Peppers, eggplantStart indoors · Feb 12 – Feb 26

Peppers, eggplantTransplant · May 7 – May 21

BeansSow outdoors · Apr 30 – May 14

Sweet cornSow outdoors · Apr 30 – May 14

Cucumbers, squashSow outdoors · Apr 30 – May 14

Fall lettuce, spinachSow outdoors · Aug 16 – Aug 30

GarlicPlant cloves · Sep 27 – Nov 1

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 23) and first fall frost (Oct 11) 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 51551 came on Mar 11 — 18 days earlier than the 1991–2020 average (Mar 29).

average
Mar 292026
Mar 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).

Soil in Malvern, IA

The soil mapped at the center of ZIP 51551 is Marshall — silty clay loam, well drained.

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

pH6.0slightly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter3%moderate

Hydrologic groupCwater soaks in slowly

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Marshall silty clay loam, 9 to 14 percent slopes, eroded.

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 51551; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Malvern, IA

Summer high87 °Faverage high, July

Winter low12 °Faverage low, January

Hot days34days a year at 90 °F or more

Freezing nights146nights a year at 32 °F or less

Growing degree days3,476base 50 °F — the season’s usable heat

Longest day15 h 08 mindaylight on June 21

Shortest day9 h 13 mindaylight on December 21

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

Precipitation35.2 inper year, rain and melted snow

Snowfall24 inper year; 47 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: Glenwood 3sw, IA (10 mi away); precipitation: Randolph, IA (8 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Silver City, IA · 11 mi

Pacific Junction, IA · 12 mi

Iowa planting zones →

Questions about 51551

What planting zone is ZIP code 51551?

ZIP code 51551 (Malvern, 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 Malvern, IA?

The median last spring frost (32 °F) near 51551 is April 23; after May 6 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Glenwood 3sw station.

When is the first frost in Malvern, IA?

The median first fall frost near 51551 is October 11, giving a median frost-free growing season of 170 days.

When should I plant tomatoes in 51551?

Start tomato seeds indoors around Feb 26 – Mar 12 and set transplants outside around Apr 30 – May 14, one to three weeks after the median last frost.

How much rain and snow does 51551 get?

About 35.2 inches of precipitation a year and 24 inches of snowfall (NOAA 1991–2020 normals, Randolph station).

How hot do summers get in Malvern, IA?

The average high peaks at 87 °F in July, with about 34 days a year at 90 °F or more.

What kind of soil does 51551 have?

The USDA soil survey maps Marshall at the center of ZIP 51551: silty clay loam, well drained, pH about 6.0 (slightly acidic).

Did spring come early in Malvern, IA in 2026?

Spring leaf-out near 51551 came on Mar 11 in 2026, 18 days earlier than the 1991–2020 average (Mar 29), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Malvern, IA?

Long-day onions: the longest day near 51551 is 15 h 08 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).