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

Planting zone for 51591 — Red Oak, IA

ZIP code 51591 (Red Oak, Montgomery County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 24 and the first fall frost October 13.

Where ZIP 51591 is

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 24
First frostOct 13
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 Red Oak, 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 Red Oak, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 24median — 50% chance of a later frost
Safe for tender plantsMay 8only 10% chance of frost after
First fall frostOctober 13median — 10% chance by Sep 26
Growing season169 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 15 and returns around October 23.

From the NOAA station Red Oak, IA — 5 miles away, elevation 1,040 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 51591

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 13 – Mar 27
SpinachSow outdoors · Mar 13 – Apr 3
Broccoli, cabbageStart indoors · Feb 13 – Feb 27
Broccoli, cabbageTransplant · Apr 3 – Apr 17
Onion setsPlant outdoors · Mar 27 – Apr 10
PotatoesPlant outdoors · Apr 3 – Apr 17
LettuceSow outdoors · Mar 27 – Apr 10
Carrots, beetsSow outdoors · Apr 3 – Apr 17
TomatoesStart indoors · Feb 27 – Mar 13
TomatoesTransplant · May 1 – May 15
Peppers, eggplantStart indoors · Feb 13 – Feb 27
Peppers, eggplantTransplant · May 8 – May 22
BeansSow outdoors · May 1 – May 15
Sweet cornSow outdoors · May 1 – May 15
Cucumbers, squashSow outdoors · May 1 – May 15
Fall lettuce, spinachSow outdoors · Aug 18 – Sep 1
GarlicPlant cloves · Sep 29 – Nov 3
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 24) and first fall frost (Oct 13) 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 51591 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).

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.

Trees 49

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican chestnut115 ft · blooms early summer · high shade tolerance · to −33 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Farborvitae50 ft · blooms mid spring · medium shade tolerance · to −33 °Fbalsam fir60 ft · blooms mid summer · low shade tolerance · to −43 °F

Shrubs 77

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falternateleaf dogwood25 ft · blooms mid spring · low shade tolerance · to −47 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °FAmerican hornbeam30 ft · blooms mid spring · low shade tolerance · to −34 °F

Wildflowers & perennials 191

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °FAmerican lotus3 ft · blooms mid summer · high shade tolerance · to −36 °FAmerican pokeweed7 ft · blooms mid summer · low shade tolerance · to −33 °F

Grasses 136

arctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °FBebb's sedge3 ft · blooms late spring · low shade tolerance · to −38 °FBicknell's sedge3 ft · blooms late spring · low shade tolerance · to −38 °Fbig bluestem6 ft · blooms summer · high shade tolerance · to −46 °Fblue grama1 ft · blooms early summer · high shade tolerance · to −43 °F

Vines 7

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Ffrost grape83 ft · blooms late spring · medium shade tolerance · to −23 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °Ftrumpet honeysuckle16 ft · blooms late summer · low shade tolerance · to −33 °F

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 Red Oak, IA.

Soil in Red Oak, IA

The soil mapped at the center of ZIP 51591 is Marshall — silty clay loam, well drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH5.9moderately acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3.3%moderate
Hydrologic groupCwater soaks in slowly
Farmland classFarmland of statewide importanceUSDA classification

Map unit: Marshall silty clay loam, 5 to 9 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 51591; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Red Oak, IA

Summer high86 °Faverage high, July
Winter low13 °Faverage low, January
Hot days26days a year at 90 °F or more
Freezing nights142nights a year at 32 °F or less
Growing degree days3,441base 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)
Precipitation37.2 inper year, rain and melted snow
Snowfall27 inper year; 44 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 33 °F, low 13 °F 33°13° JanFebruary: average high 38 °F, low 16 °F 38°16° FebMarch: average high 51 °F, low 28 °F 51°28° MarApril: average high 63 °F, low 38 °F 63°38° AprMay: average high 73 °F, low 51 °F 73°51° MayJune: average high 83 °F, low 61 °F 83°61° JunJuly: average high 86 °F, low 66 °F 86°66° JulAugust: average high 85 °F, low 63 °F 85°63° AugSeptember: average high 78 °F, low 53 °F 78°53° SepOctober: average high 66 °F, low 41 °F 66°41° OctNovember: average high 50 °F, low 28 °F 50°28° NovDecember: average high 37 °F, low 18 °F 37°18° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″6″January: 0.88 in precipitation, 7.3 in snowfall 0.9❄7 JanFebruary: 1.11 in precipitation, 8.1 in snowfall 1.1❄8 FebMarch: 2.03 in precipitation, 2.6 in snowfall 2.0❄3 MarApril: 3.83 in precipitation, 1.2 in snowfall 3.8❄1 AprMay: 5.95 in precipitation 6.0 MayJune: 5.44 in precipitation 5.4 JunJuly: 3.96 in precipitation 4.0 JulAugust: 3.89 in precipitation 3.9 AugSeptember: 3.58 in precipitation 3.6 SepOctober: 3.31 in precipitation, 0.5 in snowfall 3.3❄1 OctNovember: 1.88 in precipitation, 1.2 in snowfall 1.9❄1 NovDecember: 1.38 in precipitation, 6.5 in snowfall 1.4❄7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Red Oak, IA (5 mi away); precipitation: Red Oak, IA (5 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

515665b
Red Oak, IA · 4 mi
515735b
Stanton, IA · 5 mi
515325b
Elliott, IA · 8 mi
508645b
Villisca, IA · 10 mi
515335b
Emerson, IA · 12 mi
508475b
Grant, IA · 12 mi
515355b
Griswold, IA · 14 mi
516385b
Essex, IA · 15 mi

All 2 ZIP codes in Red Oak → · Iowa planting zones →

Questions about 51591

What planting zone is ZIP code 51591?

ZIP code 51591 (Red Oak, 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 Red Oak, IA?

The median last spring frost (32 °F) near 51591 is April 24; after May 8 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Red Oak station.

When is the first frost in Red Oak, IA?

The median first fall frost near 51591 is October 13, giving a median frost-free growing season of 169 days.

When should I plant tomatoes in 51591?

Start tomato seeds indoors around Feb 27 – Mar 13 and set transplants outside around May 1 – May 15, one to three weeks after the median last frost.

How much rain and snow does 51591 get?

About 37.2 inches of precipitation a year and 27 inches of snowfall (NOAA 1991–2020 normals, Red Oak station).

How hot do summers get in Red Oak, IA?

The average high peaks at 86 °F in July, with about 26 days a year at 90 °F or more.

What kind of soil does 51591 have?

The USDA soil survey maps Marshall at the center of ZIP 51591: silty clay loam, well drained, pH about 5.9 (moderately acidic).

Did spring come early in Red Oak, IA in 2026?

Spring leaf-out near 51591 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 Red Oak, IA?

Long-day onions: the longest day near 51591 is 15 h 08 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).