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

Planting zone for 51529 — Dunlap, IA

ZIP code 51529 (Dunlap, Harrison County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 29 and the first fall frost October 8.

Where ZIP 51529 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 29

First frostOct 8

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 Dunlap, 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 Dunlap, IA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 29median — 50% chance of a later frost

Safe for tender plantsMay 13only 10% chance of frost after

First fall frostOctober 8median — 10% chance by Sep 23

Growing season162 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 19 and returns around October 19.

From the NOAA station Logan, IA — 17 miles away, elevation 991 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 51529

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 18 – Apr 1

SpinachSow outdoors · Mar 18 – Apr 8

Broccoli, cabbageStart indoors · Feb 18 – Mar 4

Broccoli, cabbageTransplant · Apr 8 – Apr 22

Onion setsPlant outdoors · Apr 1 – Apr 15

PotatoesPlant outdoors · Apr 8 – Apr 22

LettuceSow outdoors · Apr 1 – Apr 15

Carrots, beetsSow outdoors · Apr 8 – Apr 22

TomatoesStart indoors · Mar 4 – Mar 18

TomatoesTransplant · May 6 – May 20

Peppers, eggplantStart indoors · Feb 18 – Mar 4

Peppers, eggplantTransplant · May 13 – May 27

BeansSow outdoors · May 6 – May 20

Sweet cornSow outdoors · May 6 – May 20

Cucumbers, squashSow outdoors · May 6 – May 20

Fall lettuce, spinachSow outdoors · Aug 13 – Aug 27

GarlicPlant cloves · Sep 24 – Oct 29

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 29) and first fall frost (Oct 8) 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 51529 came on Mar 24 — 11 days earlier than the 1991–2020 average (Apr 4).

average
Apr 42026
Mar 24

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 Dunlap, IA.

Soil in Dunlap, IA

The soil mapped at the center of ZIP 51529 is Monona — silt loam, well drained.

TextureSilt loama good balance for most vegetables

pH6.2slightly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter3.4%moderate

Hydrologic groupBwater soaks in moderately

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Monona silt loam, 9 to 14 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 51529; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Dunlap, IA

Summer high86 °Faverage high, July

Winter low10 °Faverage low, January

Hot days24days a year at 90 °F or more

Freezing nights154nights a year at 32 °F or less

Growing degree days3,203base 50 °F — the season’s usable heat

Longest day15 h 14 mindaylight on June 21

Shortest day9 h 08 mindaylight on December 21

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

Precipitation34.4 inper year, rain and melted snow

Snowfall29 inper year; 57 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: Logan, IA (17 mi away); precipitation: Logan, IA (17 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Iowa planting zones →

Questions about 51529

What planting zone is ZIP code 51529?

ZIP code 51529 (Dunlap, 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 Dunlap, IA?

The median last spring frost (32 °F) near 51529 is April 29; after May 13 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Logan station.

When is the first frost in Dunlap, IA?

The median first fall frost near 51529 is October 8, giving a median frost-free growing season of 162 days.

When should I plant tomatoes in 51529?

Start tomato seeds indoors around Mar 4 – Mar 18 and set transplants outside around May 6 – May 20, one to three weeks after the median last frost.

How much rain and snow does 51529 get?

About 34.4 inches of precipitation a year and 29 inches of snowfall (NOAA 1991–2020 normals, Logan station).

How hot do summers get in Dunlap, IA?

The average high peaks at 86 °F in July, with about 24 days a year at 90 °F or more.

What kind of soil does 51529 have?

The USDA soil survey maps Monona at the center of ZIP 51529: silt loam, well drained, pH about 6.2 (slightly acidic).

Did spring come early in Dunlap, IA in 2026?

Spring leaf-out near 51529 came on Mar 24 in 2026, 11 days earlier than the 1991–2020 average (Apr 4), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Dunlap, IA?

Long-day onions: the longest day near 51529 is 15 h 14 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 51529 change?

Yes. The 2012 USDA map put 51529 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.