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

Planting zone for 52249 — Keystone, IA

ZIP code 52249 (Keystone, Benton 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 10.

Where ZIP 52249 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 10

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 Keystone, 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 Keystone, 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 11only 10% chance of frost after

First fall frostOctober 10median — 10% chance by Sep 26

Growing season165 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 16 and returns around October 21.

From the NOAA station Belle Plaine, IA — 10 miles away, elevation 810 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 52249

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 15 – Aug 29

GarlicPlant cloves · Sep 26 – Oct 31

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 28) and first fall frost (Oct 10) 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 52249 came on Mar 25 — 14 days earlier than the 1991–2020 average (Apr 8).

average
Apr 82026
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 Keystone, IA

The soil mapped at the center of ZIP 52249 is Dinsdale — silty clay loam, moderately well drained.

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

pH6.4slightly acidic; most vegetables like 6.0–7.0

DrainageModerately well drainednatural drainage class

Organic matter3.5%moderate

Hydrologic groupCwater soaks in slowly

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Dinsdale 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 52249; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Keystone, IA

Summer high84 °Faverage high, July

Winter low10 °Faverage low, January

Hot days14days a year at 90 °F or more

Freezing nights153nights a year at 32 °F or less

Growing degree days2,989base 50 °F — the season’s usable heat

Longest day15 h 15 mindaylight on June 21

Shortest day9 h 07 mindaylight on December 21

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

Precipitation36 inper year, rain and melted snow

Snowfall28 inper year; 55 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: Belle Plaine, IA (10 mi away); precipitation: Belle Plaine, IA (10 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

Blairstown, IA · 9 mi

Belle Plaine, IA · 10 mi

522245a

Dysart, IA · 11 mi

Iowa planting zones →

Questions about 52249

What planting zone is ZIP code 52249?

ZIP code 52249 (Keystone, 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 Keystone, IA?

The median last spring frost (32 °F) near 52249 is April 28; after May 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Belle Plaine station.

When is the first frost in Keystone, IA?

The median first fall frost near 52249 is October 10, giving a median frost-free growing season of 165 days.

When should I plant tomatoes in 52249?

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 52249 get?

About 36 inches of precipitation a year and 28 inches of snowfall (NOAA 1991–2020 normals, Belle Plaine station).

How hot do summers get in Keystone, IA?

The average high peaks at 84 °F in July, with about 14 days a year at 90 °F or more.

What kind of soil does 52249 have?

The USDA soil survey maps Dinsdale at the center of ZIP 52249: silty clay loam, moderately well drained, pH about 6.4 (slightly acidic).

Did spring come early in Keystone, IA in 2026?

Spring leaf-out near 52249 came on Mar 25 in 2026, 14 days earlier than the 1991–2020 average (Apr 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Keystone, IA?

Long-day onions: the longest day near 52249 is 15 h 15 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).