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

Planting zone for 52301 — Marengo, IA

ZIP code 52301 (Marengo, Iowa County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is April 28 and the first fall frost October 9.

Where ZIP 52301 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.

Zone5a−20 to −15 °F
Coldest night−28.9 to −26.1 °C
Last frostApr 28
First frostOct 9
2012 zone5a

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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Marengo, 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 Marengo, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 28median — 50% chance of a later frost
Safe for tender plantsMay 12only 10% chance of frost after
First fall frostOctober 9median — 10% chance by Sep 24
Growing season164 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 18 and returns around October 19.

From the NOAA station Williamsburg 1e, IA — 9 miles away, elevation 781 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 52301

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 17 – Mar 31
SpinachSow outdoors · Mar 17 – Apr 7
Broccoli, cabbageStart indoors · Feb 17 – Mar 3
Broccoli, cabbageTransplant · Apr 7 – Apr 21
Onion setsPlant outdoors · Mar 31 – Apr 14
PotatoesPlant outdoors · Apr 7 – Apr 21
LettuceSow outdoors · Mar 31 – Apr 14
Carrots, beetsSow outdoors · Apr 7 – Apr 21
TomatoesStart indoors · Mar 3 – Mar 17
TomatoesTransplant · May 5 – May 19
Peppers, eggplantStart indoors · Feb 17 – Mar 3
Peppers, eggplantTransplant · May 12 – May 26
BeansSow outdoors · May 5 – May 19
Sweet cornSow outdoors · May 5 – May 19
Cucumbers, squashSow outdoors · May 5 – May 19
Fall lettuce, spinachSow outdoors · Aug 14 – Aug 28
GarlicPlant cloves · Sep 25 – Oct 30
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 28) and first fall frost (Oct 9) 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 52301 came on Mar 25 — 12 days earlier than the 1991–2020 average (Apr 6).

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 5a in Iowa

461 plants native to the lower 48 states, recorded in Iowa, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. Each links to its USDA PLANTS profile.

Trees 46

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 185

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 133

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 Marengo, IA.

Soil in Marengo, IA

The soil mapped at the center of ZIP 52301 is Tama — silty clay loam, well drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH6.5neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3.5%moderate
Hydrologic groupCwater soaks in slowly
Farmland classprime farmlandUSDA classification

Map unit: Tama silty clay loam, terrace, 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 52301; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Marengo, IA

Summer high84 °Faverage high, July
Winter low10 °Faverage low, January
Hot days17days a year at 90 °F or more
Freezing nights151nights a year at 32 °F or less
Growing degree days2,981base 50 °F — the season’s usable heat
Longest day15 h 13 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)
Precipitation37.7 inper year, rain and melted snow
Snowfall28 inper year; 52 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 28 °F, low 10 °F 28°10° JanFebruary: average high 33 °F, low 14 °F 33°14° FebMarch: average high 47 °F, low 26 °F 47°26° MarApril: average high 60 °F, low 36 °F 60°36° AprMay: average high 71 °F, low 49 °F 71°49° MayJune: average high 81 °F, low 59 °F 81°59° JunJuly: average high 84 °F, low 63 °F 84°63° JulAugust: average high 82 °F, low 60 °F 82°60° AugSeptember: average high 76 °F, low 51 °F 76°51° SepOctober: average high 63 °F, low 39 °F 63°39° OctNovember: average high 47 °F, low 27 °F 47°27° NovDecember: average high 34 °F, low 16 °F 34°16° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″January: 1.16 in precipitation, 7.6 in snowfall 1.2❄8 JanFebruary: 1.46 in precipitation, 7.7 in snowfall 1.5❄8 FebMarch: 2.19 in precipitation, 3.6 in snowfall 2.2❄4 MarApril: 3.92 in precipitation, 0.9 in snowfall 3.9❄1 AprMay: 4.85 in precipitation, 0.1 in snowfall 4.8 MayJune: 4.80 in precipitation 4.8 JunJuly: 4.32 in precipitation 4.3 JulAugust: 4.47 in precipitation 4.5 AugSeptember: 3.80 in precipitation 3.8 SepOctober: 2.83 in precipitation, 0.3 in snowfall 2.8 OctNovember: 2.20 in precipitation, 1.6 in snowfall 2.2❄2 NovDecember: 1.69 in precipitation, 6.3 in snowfall 1.7❄6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Williamsburg 1e, IA (9 mi away); precipitation: Williamsburg 1e, IA (9 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.

522205a
Conroy, IA · 6 mi
523345a
South Amana, IA · 8 mi
522095a
Blairstown, IA · 8 mi
522515a
Ladora, IA · 8 mi
523075b
Middle Amana, IA · 9 mi
522575a
Luzerne, IA · 10 mi
522035b
Amana, IA · 10 mi
523545a
Watkins, IA · 10 mi

Iowa planting zones →

Questions about 52301

What planting zone is ZIP code 52301?

ZIP code 52301 (Marengo, IA) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Marengo, IA?

The median last spring frost (32 °F) near 52301 is April 28; after May 12 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Williamsburg 1e station.

When is the first frost in Marengo, IA?

The median first fall frost near 52301 is October 9, giving a median frost-free growing season of 164 days.

When should I plant tomatoes in 52301?

Start tomato seeds indoors around Mar 3 – Mar 17 and set transplants outside around May 5 – May 19, one to three weeks after the median last frost.

How much rain and snow does 52301 get?

About 37.7 inches of precipitation a year and 28 inches of snowfall (NOAA 1991–2020 normals, Williamsburg 1e station).

How hot do summers get in Marengo, IA?

The average high peaks at 84 °F in July, with about 17 days a year at 90 °F or more.

What kind of soil does 52301 have?

The USDA soil survey maps Tama at the center of ZIP 52301: silty clay loam, well drained, pH about 6.5 (neutral).

Did spring come early in Marengo, IA in 2026?

Spring leaf-out near 52301 came on Mar 25 in 2026, 12 days earlier than the 1991–2020 average (Apr 6), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Marengo, IA?

Long-day onions: the longest day near 52301 is 15 h 13 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).