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

Planting zone for 50552 — Knierim, IA

ZIP code 50552 (Knierim, Calhoun County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is April 26 and the first fall frost October 10.

Where ZIP 50552 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 26
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 Knierim, 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 Knierim, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 26median — 50% chance of a later frost
Safe for tender plantsMay 6only 10% chance of frost after
First fall frostOctober 10median — 10% chance by Sep 27
Growing season167 daysfrost-free, median

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

From the NOAA station Rockwell City, IA — 9 miles away, elevation 1,214 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 50552

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 15 – Mar 29
SpinachSow outdoors · Mar 15 – Apr 5
Broccoli, cabbageStart indoors · Feb 15 – Mar 1
Broccoli, cabbageTransplant · Apr 5 – Apr 19
Onion setsPlant outdoors · Mar 29 – Apr 12
PotatoesPlant outdoors · Apr 5 – Apr 19
LettuceSow outdoors · Mar 29 – Apr 12
Carrots, beetsSow outdoors · Apr 5 – Apr 19
TomatoesStart indoors · Mar 1 – Mar 15
TomatoesTransplant · May 3 – May 17
Peppers, eggplantStart indoors · Feb 15 – Mar 1
Peppers, eggplantTransplant · May 10 – May 24
BeansSow outdoors · May 3 – May 17
Sweet cornSow outdoors · May 3 – May 17
Cucumbers, squashSow outdoors · May 3 – May 17
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 26) 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 50552 came on Mar 25 — 15 days earlier than the 1991–2020 average (Apr 9).

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 Knierim, IA.

Soil in Knierim, IA

The soil mapped at the center of ZIP 50552 is Webster — 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 matter7%high
Hydrologic groupC/Dslow when drained; wet otherwise
Farmland classPrime farmland if drainedUSDA classification

Map unit: Webster clay 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 50552; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Knierim, IA

Summer high83 °Faverage high, July
Winter low8 °Faverage low, January
Hot days13days a year at 90 °F or more
Freezing nights154nights a year at 32 °F or less
Growing degree days2,888base 50 °F — the season’s usable heat
Longest day15 h 18 mindaylight on June 21
Shortest day9 h 04 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation33.8 inper year, rain and melted snow
Snowfall32 inper year; 74 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 27 °F, low 8 °F 27°8° JanFebruary: average high 31 °F, low 12 °F 31°12° FebMarch: average high 45 °F, low 24 °F 45°24° MarApril: average high 59 °F, low 36 °F 59°36° AprMay: average high 70 °F, low 49 °F 70°49° MayJune: average high 80 °F, low 60 °F 80°60° JunJuly: average high 83 °F, low 63 °F 83°63° JulAugust: average high 81 °F, low 61 °F 81°61° AugSeptember: average high 75 °F, low 51 °F 75°51° SepOctober: average high 62 °F, low 38 °F 62°38° OctNovember: average high 46 °F, low 25 °F 46°25° NovDecember: average high 32 °F, low 15 °F 32°15° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″6″January: 0.76 in precipitation, 7.4 in snowfall 0.8❄7 JanFebruary: 0.99 in precipitation, 7.6 in snowfall 1.0❄8 FebMarch: 1.99 in precipitation, 4.9 in snowfall 2.0❄5 MarApril: 3.76 in precipitation, 1.9 in snowfall 3.8❄2 AprMay: 5.02 in precipitation 5.0 MayJune: 5.04 in precipitation 5.0 JunJuly: 3.54 in precipitation 3.5 JulAugust: 4.53 in precipitation 4.5 AugSeptember: 2.95 in precipitation 3.0 SepOctober: 2.35 in precipitation, 0.6 in snowfall 2.4❄1 OctNovember: 1.48 in precipitation, 2.4 in snowfall 1.5❄2 NovDecember: 1.34 in precipitation, 7.3 in snowfall 1.3❄7 Dec

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

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

505865a
Somers, IA · 4 mi
505185a
Barnum, IA · 6 mi
505635a
Manson, IA · 6 mi
505665a
Moorland, IA · 7 mi
505795a
Rockwell City, IA · 10 mi
505235a
Callender, IA · 10 mi
505245a
Clare, IA · 11 mi
505385a
Farnhamville, IA · 12 mi

Iowa planting zones →

Questions about 50552

What planting zone is ZIP code 50552?

ZIP code 50552 (Knierim, 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 Knierim, IA?

The median last spring frost (32 °F) near 50552 is April 26; after May 6 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Rockwell City station.

When is the first frost in Knierim, IA?

The median first fall frost near 50552 is October 10, giving a median frost-free growing season of 167 days.

When should I plant tomatoes in 50552?

Start tomato seeds indoors around Mar 1 – Mar 15 and set transplants outside around May 3 – May 17, one to three weeks after the median last frost.

How much rain and snow does 50552 get?

About 33.8 inches of precipitation a year and 32 inches of snowfall (NOAA 1991–2020 normals, Rockwell City station).

How hot do summers get in Knierim, IA?

The average high peaks at 83 °F in July, with about 13 days a year at 90 °F or more.

What kind of soil does 50552 have?

The USDA soil survey maps Webster at the center of ZIP 50552: clay loam, poorly drained, pH about 6.5 (neutral).

Did spring come early in Knierim, IA in 2026?

Spring leaf-out near 50552 came on Mar 25 in 2026, 15 days earlier than the 1991–2020 average (Apr 9), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Knierim, IA?

Long-day onions: the longest day near 50552 is 15 h 18 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).