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

Planting zone for 51576 — Underwood, IA

ZIP code 51576 (Underwood, Pottawattamie County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 18 and the first fall frost October 21.

Where ZIP 51576 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 18
First frostOct 21
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 Underwood, 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 Underwood, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 18median — 50% chance of a later frost
Safe for tender plantsApril 30only 10% chance of frost after
First fall frostOctober 21median — 10% chance by Oct 6
Growing season185 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 8 and returns around October 30.

From the NOAA station Omaha Eppley Airfield, NE — 11 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 51576

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 7 – Mar 21
SpinachSow outdoors · Mar 7 – Mar 28
Broccoli, cabbageStart indoors · Feb 7 – Feb 21
Broccoli, cabbageTransplant · Mar 28 – Apr 11
Onion setsPlant outdoors · Mar 21 – Apr 4
PotatoesPlant outdoors · Mar 28 – Apr 11
LettuceSow outdoors · Mar 21 – Apr 4
Carrots, beetsSow outdoors · Mar 28 – Apr 11
TomatoesStart indoors · Feb 21 – Mar 7
TomatoesTransplant · Apr 25 – May 9
Peppers, eggplantStart indoors · Feb 7 – Feb 21
Peppers, eggplantTransplant · May 2 – May 16
BeansSow outdoors · Apr 25 – May 9
Sweet cornSow outdoors · Apr 25 – May 9
Cucumbers, squashSow outdoors · Apr 25 – May 9
Fall lettuce, spinachSow outdoors · Aug 26 – Sep 9
GarlicPlant cloves · Oct 7 – Nov 11
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 18) and first fall frost (Oct 21) 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 51576 came on Mar 15 — 16 days earlier than the 1991–2020 average (Mar 31).

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 Underwood, IA

The soil mapped at the center of ZIP 51576 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 classprime farmlandUSDA classification

Map unit: Monona silt loam, 2 to 5 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 51576; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Underwood, IA

Summer high88 °Faverage high, July
Winter low15 °Faverage low, January
Hot days33days a year at 90 °F or more
Freezing nights135nights a year at 32 °F or less
Growing degree days3,787base 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)
Precipitation34.1 inper year, rain and melted snow
Snowfall27 inper year; 46 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 34 °F, low 15 °F 34°15° JanFebruary: average high 39 °F, low 19 °F 39°19° FebMarch: average high 52 °F, low 30 °F 52°30° MarApril: average high 64 °F, low 41 °F 64°41° AprMay: average high 75 °F, low 53 °F 75°53° MayJune: average high 84 °F, low 63 °F 84°63° JunJuly: average high 88 °F, low 68 °F 88°68° JulAugust: average high 86 °F, low 66 °F 86°66° AugSeptember: average high 79 °F, low 56 °F 79°56° SepOctober: average high 66 °F, low 43 °F 66°43° OctNovember: average high 50 °F, low 30 °F 50°30° NovDecember: average high 38 °F, low 20 °F 38°20° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″6″January: 0.73 in precipitation, 5.5 in snowfall 0.7❄6 JanFebruary: 0.83 in precipitation, 9.7 in snowfall 0.8❄10 FebMarch: 1.76 in precipitation, 3.1 in snowfall 1.8❄3 MarApril: 3.77 in precipitation, 0.8 in snowfall 3.8❄1 AprMay: 5.19 in precipitation, 0.2 in snowfall 5.2 MayJune: 5.11 in precipitation 5.1 JunJuly: 3.74 in precipitation 3.7 JulAugust: 4.15 in precipitation 4.2 AugSeptember: 3.23 in precipitation 3.2 SepOctober: 2.68 in precipitation, 0.7 in snowfall 2.7❄1 OctNovember: 1.50 in precipitation, 0.8 in snowfall 1.5❄1 NovDecember: 1.40 in precipitation, 6.5 in snowfall 1.4❄7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Omaha Eppley Airfield, NE (11 mi away); precipitation: Underwood, IA (2 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.

515485b
Mc Clelland, IA · 6 mi
515595b
Neola, IA · 6 mi
515425b
Honey Creek, IA · 7 mi
515265b
Crescent, IA · 8 mi
515535b
Minden, IA · 9 mi
681106a
Omaha, NE · 11 mi
515026a
Council Bluffs, IA · 11 mi
515755b
Treynor, IA · 11 mi

Iowa planting zones →

Questions about 51576

What planting zone is ZIP code 51576?

ZIP code 51576 (Underwood, 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 Underwood, IA?

The median last spring frost (32 °F) near 51576 is April 18; after April 30 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Omaha Eppley Airfield station.

When is the first frost in Underwood, IA?

The median first fall frost near 51576 is October 21, giving a median frost-free growing season of 185 days.

When should I plant tomatoes in 51576?

Start tomato seeds indoors around Feb 21 – Mar 7 and set transplants outside around Apr 25 – May 9, one to three weeks after the median last frost.

How much rain and snow does 51576 get?

About 34.1 inches of precipitation a year and 27 inches of snowfall (NOAA 1991–2020 normals, Underwood station).

How hot do summers get in Underwood, IA?

The average high peaks at 88 °F in July, with about 33 days a year at 90 °F or more.

What kind of soil does 51576 have?

The USDA soil survey maps Monona at the center of ZIP 51576: silt loam, well drained, pH about 6.2 (slightly acidic).

Did spring come early in Underwood, IA in 2026?

Spring leaf-out near 51576 came on Mar 15 in 2026, 16 days earlier than the 1991–2020 average (Mar 31), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Underwood, IA?

Long-day onions: the longest day near 51576 is 15 h 10 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).