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

Planting zone for 51201 — Sheldon, IA

ZIP code 51201 (Sheldon, O'Brien County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 5 and the first fall frost September 28.

Where ZIP 51201 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 frostMay 5

First frostSep 28

2012 zone4b

Was 4b 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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Sheldon, 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 Sheldon, IA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 5median — 50% chance of a later frost

Safe for tender plantsMay 18only 10% chance of frost after

First fall frostSeptember 28median — 10% chance by Sep 14

Growing season145 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 28 and returns around October 6.

From the NOAA station Sheldon, IA — within 1 mile, elevation 1,421 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 51201

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 24 – Apr 7

SpinachSow outdoors · Mar 24 – Apr 14

Broccoli, cabbageStart indoors · Feb 24 – Mar 10

Broccoli, cabbageTransplant · Apr 14 – Apr 28

Onion setsPlant outdoors · Apr 7 – Apr 21

PotatoesPlant outdoors · Apr 14 – Apr 28

LettuceSow outdoors · Apr 7 – Apr 21

Carrots, beetsSow outdoors · Apr 14 – Apr 28

TomatoesStart indoors · Mar 10 – Mar 24

TomatoesTransplant · May 12 – May 26

Peppers, eggplantStart indoors · Feb 24 – Mar 10

Peppers, eggplantTransplant · May 19 – Jun 2

BeansSow outdoors · May 12 – May 26

Sweet cornSow outdoors · May 12 – May 26

Cucumbers, squashSow outdoors · May 12 – May 26

Fall lettuce, spinachSow outdoors · Aug 3 – Aug 17

GarlicPlant cloves · Sep 14 – Oct 19

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 5) and first fall frost (Sep 28) 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 51201 came on Mar 25 — 17 days earlier than the 1991–2020 average (Apr 11).

average
Apr 112026
Mar 25

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 Sheldon, IA

The soil mapped at the center of ZIP 51201 is Sac — silty clay loam, moderately well drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up

pH5.9moderately acidic; most vegetables like 6.0–7.0

DrainageModerately well drainednatural drainage class

Organic matter3.5%moderate

Hydrologic groupCwater soaks in slowly

Farmland classprime farmlandUSDA classification

Map unit: Sac silty clay loam, 2 to 5 percent slopes, eroded.

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 51201; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Sheldon, IA

Summer high83 °Faverage high, July

Winter low5 °Faverage low, January

Hot days12days a year at 90 °F or more

Freezing nights171nights a year at 32 °F or less

Growing degree days2,576base 50 °F — the season’s usable heat

Longest day15 h 23 mindaylight on June 21

Shortest day8 h 59 mindaylight on December 21

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

Precipitation31.1 inper year, rain and melted snow

Snowfall41 inper year; 80 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: Sheldon, IA (within 1 mile); precipitation: Sheldon, IA (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

Granville, IA · 14 mi

Iowa planting zones →

Questions about 51201

What planting zone is ZIP code 51201?

ZIP code 51201 (Sheldon, 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 Sheldon, IA?

The median last spring frost (32 °F) near 51201 is May 5; after May 18 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Sheldon station.

When is the first frost in Sheldon, IA?

The median first fall frost near 51201 is September 28, giving a median frost-free growing season of 145 days.

When should I plant tomatoes in 51201?

Start tomato seeds indoors around Mar 10 – Mar 24 and set transplants outside around May 12 – May 26, one to three weeks after the median last frost.

How much rain and snow does 51201 get?

About 31.1 inches of precipitation a year and 41 inches of snowfall (NOAA 1991–2020 normals, Sheldon station).

How hot do summers get in Sheldon, IA?

The average high peaks at 83 °F in July, with about 12 days a year at 90 °F or more.

What kind of soil does 51201 have?

The USDA soil survey maps Sac at the center of ZIP 51201: silty clay loam, moderately well drained, pH about 5.9 (moderately acidic).

Did spring come early in Sheldon, IA in 2026?

Spring leaf-out near 51201 came on Mar 25 in 2026, 17 days earlier than the 1991–2020 average (Apr 11), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Sheldon, IA?

Long-day onions: the longest day near 51201 is 15 h 23 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 51201 change?

Yes. The 2012 USDA map put 51201 in zone 4b; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.