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

Planting zone for 50464 — Plymouth, IA

ZIP code 50464 (Plymouth, Cerro Gordo County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is April 29 and the first fall frost October 7.

Where ZIP 50464 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 29

First frostOct 7

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 Plymouth, 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 Plymouth, 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 9only 10% chance of frost after

First fall frostOctober 7median — 10% chance by Sep 25

Growing season161 daysfrost-free, median

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

From the NOAA station Mason City, IA — 9 miles away, elevation 1,106 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 50464

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 12 – Aug 26

GarlicPlant cloves · Sep 23 – Oct 28

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 29) and first fall frost (Oct 7) 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 50464 came on Mar 30 — 15 days earlier than the 1991–2020 average (Apr 14).

average
Apr 142026
Mar 30

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.

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 Plymouth, IA.

Soil in Plymouth, IA

The soil mapped at the center of ZIP 50464 is Marshan — clay loam, poorly drained.

TextureClay loamholds water and nutrients; slow to drain and warm up

pH6.5neutral; most vegetables like 6.0–7.0

DrainagePoorly drainedconsider raised beds

Organic matter5.5%high

Hydrologic groupC/Dslow when drained; wet otherwise

Farmland classPrime farmland if drainedUSDA classification

Map unit: Marshan clay loam, 0 to 2 percent slopes, rarely flooded.

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 50464; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Plymouth, IA

Summer high82 °Faverage high, July

Winter low7 °Faverage low, January

Hot days9days a year at 90 °F or more

Freezing nights161nights a year at 32 °F or less

Growing degree days2,638base 50 °F — the season’s usable heat

Longest day15 h 24 mindaylight on June 21

Shortest day8 h 58 mindaylight on December 21

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

Precipitation36.3 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Mason City, IA (9 mi away); precipitation: Mason City, IA (9 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

504675a

Rock Falls, IA · 3 mi

504405a

Grafton, IA · 6 mi

504585a

Nora Springs, IA · 7 mi

504565a

Manly, IA · 8 mi

504015a

Mason City, IA · 9 mi

504025a

Mason City, IA · 9 mi

Iowa planting zones →

Questions about 50464

What planting zone is ZIP code 50464?

ZIP code 50464 (Plymouth, 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 Plymouth, IA?

The median last spring frost (32 °F) near 50464 is April 29; after May 9 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Mason City station.

When is the first frost in Plymouth, IA?

The median first fall frost near 50464 is October 7, giving a median frost-free growing season of 161 days.

When should I plant tomatoes in 50464?

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 50464 get?

About 36.3 inches of precipitation a year (NOAA 1991–2020 normals, Mason City station).

How hot do summers get in Plymouth, IA?

The average high peaks at 82 °F in July, with about 9 days a year at 90 °F or more.

What kind of soil does 50464 have?

The USDA soil survey maps Marshan at the center of ZIP 50464: clay loam, poorly drained, pH about 6.5 (neutral).

Did spring come early in Plymouth, IA in 2026?

Spring leaf-out near 50464 came on Mar 30 in 2026, 15 days earlier than the 1991–2020 average (Apr 14), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Plymouth, IA?

Long-day onions: the longest day near 50464 is 15 h 24 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).