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

Planting zone for 50131 — Johnston, IA

ZIP code 50131 (Johnston, Polk County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 19 and the first fall frost October 18.

Where ZIP 50131 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.

Zone5b−15 to −10 °F
Coldest night−26.1 to −23.3 °C
Last frostApr 19
First frostOct 18
2012 zone5a

Was 5a 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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Johnston, 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 Johnston, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 19median — 50% chance of a later frost
Safe for tender plantsMay 3only 10% chance of frost after
First fall frostOctober 18median — 10% chance by Oct 1
Growing season179 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 9 and returns around October 27.

From the NOAA station Des Moines Wsfo-Johnston, IA — 2 miles away, elevation 958 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 50131

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 8 – Mar 22
SpinachSow outdoors · Mar 8 – Mar 29
Broccoli, cabbageStart indoors · Feb 8 – Feb 22
Broccoli, cabbageTransplant · Mar 29 – Apr 12
Onion setsPlant outdoors · Mar 22 – Apr 5
PotatoesPlant outdoors · Mar 29 – Apr 12
LettuceSow outdoors · Mar 22 – Apr 5
Carrots, beetsSow outdoors · Mar 29 – Apr 12
TomatoesStart indoors · Feb 22 – Mar 8
TomatoesTransplant · Apr 26 – May 10
Peppers, eggplantStart indoors · Feb 8 – Feb 22
Peppers, eggplantTransplant · May 3 – May 17
BeansSow outdoors · Apr 26 – May 10
Sweet cornSow outdoors · Apr 26 – May 10
Cucumbers, squashSow outdoors · Apr 26 – May 10
Fall lettuce, spinachSow outdoors · Aug 23 – Sep 6
GarlicPlant cloves · Oct 4 – Nov 8
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 19) and first fall frost (Oct 18) 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 50131 came on Mar 20 — 15 days earlier than the 1991–2020 average (Apr 4).

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 Johnston, IA

The soil mapped at the center of ZIP 50131 is Dickinson — fine sandy loam, somewhat excessively drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding
pH6.5neutral; most vegetables like 6.0–7.0
DrainageSomewhat excessively drainednatural drainage class
Organic matter2%moderate
Hydrologic groupAwater soaks in fast
Farmland classprime farmlandUSDA classification

Map unit: Dickinson fine sandy loam, 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 50131; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Johnston, IA

Summer high85 °Faverage high, July
Winter low13 °Faverage low, January
Hot days18days a year at 90 °F or more
Freezing nights135nights a year at 32 °F or less
Growing degree days3,361base 50 °F — the season’s usable heat
Longest day15 h 12 mindaylight on June 21
Shortest day9 h 09 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation36.6 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 30 °F, low 13 °F 30°13° JanFebruary: average high 35 °F, low 17 °F 35°17° FebMarch: average high 49 °F, low 29 °F 49°29° MarApril: average high 62 °F, low 40 °F 62°40° AprMay: average high 72 °F, low 52 °F 72°52° MayJune: average high 81 °F, low 62 °F 81°62° JunJuly: average high 85 °F, low 66 °F 85°66° JulAugust: average high 83 °F, low 64 °F 83°64° AugSeptember: average high 76 °F, low 55 °F 76°55° SepOctober: average high 63 °F, low 43 °F 63°43° OctNovember: average high 48 °F, low 30 °F 48°30° NovDecember: average high 35 °F, low 19 °F 35°19° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 0.95 in precipitation 0.9 JanFebruary: 1.28 in precipitation 1.3 FebMarch: 2.13 in precipitation 2.1 MarApril: 3.93 in precipitation 3.9 AprMay: 5.09 in precipitation 5.1 MayJune: 5.23 in precipitation 5.2 JunJuly: 4.39 in precipitation 4.4 JulAugust: 4.19 in precipitation 4.2 AugSeptember: 3.48 in precipitation 3.5 SepOctober: 2.58 in precipitation 2.6 OctNovember: 1.93 in precipitation 1.9 NovDecember: 1.41 in precipitation 1.4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Des Moines Wsfo-Johnston, IA (2 mi away); precipitation: Johnston 3.7 Nnw, IA (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

501115b
Grimes, IA · 4 mi
503225b
Urbandale, IA · 4 mi
503985b
Urbandale, IA · 5 mi
500235b
Ankeny, IA · 5 mi
503105b
Des Moines, IA · 5 mi
503135b
Des Moines, IA · 6 mi
503245b
Windsor Heights, IA · 6 mi
501095b
Granger, IA · 7 mi

Iowa planting zones →

Questions about 50131

What planting zone is ZIP code 50131?

ZIP code 50131 (Johnston, 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 Johnston, IA?

The median last spring frost (32 °F) near 50131 is April 19; after May 3 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Des Moines Wsfo-Johnston station.

When is the first frost in Johnston, IA?

The median first fall frost near 50131 is October 18, giving a median frost-free growing season of 179 days.

When should I plant tomatoes in 50131?

Start tomato seeds indoors around Feb 22 – Mar 8 and set transplants outside around Apr 26 – May 10, one to three weeks after the median last frost.

How much rain and snow does 50131 get?

About 36.6 inches of precipitation a year (NOAA 1991–2020 normals, Johnston 3.7 Nnw station).

How hot do summers get in Johnston, IA?

The average high peaks at 85 °F in July, with about 18 days a year at 90 °F or more.

What kind of soil does 50131 have?

The USDA soil survey maps Dickinson at the center of ZIP 50131: fine sandy loam, somewhat excessively drained, pH about 6.5 (neutral).

Did spring come early in Johnston, IA in 2026?

Spring leaf-out near 50131 came on Mar 20 in 2026, 15 days earlier than the 1991–2020 average (Apr 4), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Johnston, IA?

Long-day onions: the longest day near 50131 is 15 h 12 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 50131 change?

Yes. The 2012 USDA map put 50131 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.