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

Planting zone for 51535 — Griswold, IA

ZIP code 51535 (Griswold, Cass County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 23 and the first fall frost October 14.

Where ZIP 51535 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 23
First frostOct 14
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 Griswold, 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 Griswold, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 23median — 50% chance of a later frost
Safe for tender plantsMay 5only 10% chance of frost after
First fall frostOctober 14median — 10% chance by Sep 30
Growing season174 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 15 and returns around October 25.

From the NOAA station Oakland, IA — 14 miles away, elevation 1,260 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 51535

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 12 – Mar 26
SpinachSow outdoors · Mar 12 – Apr 2
Broccoli, cabbageStart indoors · Feb 12 – Feb 26
Broccoli, cabbageTransplant · Apr 2 – Apr 16
Onion setsPlant outdoors · Mar 26 – Apr 9
PotatoesPlant outdoors · Apr 2 – Apr 16
LettuceSow outdoors · Mar 26 – Apr 9
Carrots, beetsSow outdoors · Apr 2 – Apr 16
TomatoesStart indoors · Feb 26 – Mar 12
TomatoesTransplant · Apr 30 – May 14
Peppers, eggplantStart indoors · Feb 12 – Feb 26
Peppers, eggplantTransplant · May 7 – May 21
BeansSow outdoors · Apr 30 – May 14
Sweet cornSow outdoors · Apr 30 – May 14
Cucumbers, squashSow outdoors · Apr 30 – May 14
Fall lettuce, spinachSow outdoors · Aug 19 – Sep 2
GarlicPlant cloves · Sep 30 – Nov 4
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 23) and first fall frost (Oct 14) 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 51535 came on Mar 15 — 17 days earlier than the 1991–2020 average (Apr 1).

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 5b in Iowa

473 plants native to the lower 48 states, recorded in Iowa, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. Each links to its USDA PLANTS profile.

Trees 49

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 191

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 136

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 Griswold, IA.

Soil in Griswold, IA

The soil mapped at the center of ZIP 51535 is Nevin — silty clay loam, somewhat poorly drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH6.2slightly acidic; most vegetables like 6.0–7.0
DrainageSomewhat poorly drainedconsider raised beds
Organic matter5%high
Hydrologic groupC/Dslow when drained; wet otherwise
Farmland classprime farmlandUSDA classification

Map unit: Nevin silty 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 51535; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Griswold, IA

Summer high85 °Faverage high, July
Winter low12 °Faverage low, January
Hot days20days a year at 90 °F or more
Freezing nights148nights a year at 32 °F or less
Growing degree days3,216base 50 °F — the season’s usable heat
Longest day15 h 09 mindaylight on June 21
Shortest day9 h 12 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation36.4 inper year, rain and melted snow
Snowfall28 inper year; 46 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 30 °F, low 12 °F 30°12° JanFebruary: average high 35 °F, low 16 °F 35°16° FebMarch: average high 49 °F, low 27 °F 49°27° MarApril: average high 62 °F, low 37 °F 62°37° AprMay: average high 72 °F, low 50 °F 72°50° MayJune: average high 82 °F, low 61 °F 82°61° JunJuly: average high 85 °F, low 64 °F 85°64° JulAugust: average high 83 °F, low 62 °F 83°62° AugSeptember: average high 77 °F, low 53 °F 77°53° SepOctober: average high 64 °F, low 41 °F 64°41° OctNovember: average high 48 °F, low 28 °F 48°28° NovDecember: average high 35 °F, low 17 °F 35°17° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″6″January: 0.85 in precipitation, 6.7 in snowfall 0.8❄7 JanFebruary: 1.07 in precipitation, 8 in snowfall 1.1❄8 FebMarch: 1.99 in precipitation, 3.4 in snowfall 2.0❄3 MarApril: 3.90 in precipitation, 1.1 in snowfall 3.9❄1 AprMay: 5.42 in precipitation, 0.1 in snowfall 5.4 MayJune: 5.28 in precipitation 5.3 JunJuly: 3.58 in precipitation 3.6 JulAugust: 4.87 in precipitation 4.9 AugSeptember: 3.62 in precipitation 3.6 SepOctober: 2.97 in precipitation, 1 in snowfall 3.0❄1 OctNovember: 1.57 in precipitation, 1.2 in snowfall 1.6❄1 NovDecember: 1.31 in precipitation, 6.5 in snowfall 1.3❄7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Oakland, IA (14 mi away); precipitation: Oakland, IA (14 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

1 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

515445b
Lewis, IA · 6 mi
515325b
Elliott, IA · 6 mi
508475b
Grant, IA · 9 mi
508435b
Cumberland, IA · 13 mi
515915b
Red Oak, IA · 14 mi
500225a
Atlantic, IA · 15 mi
515255b
Carson, IA · 15 mi
515605b
Oakland, IA · 15 mi

Iowa planting zones →

Questions about 51535

What planting zone is ZIP code 51535?

ZIP code 51535 (Griswold, 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 Griswold, IA?

The median last spring frost (32 °F) near 51535 is April 23; after May 5 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Oakland station.

When is the first frost in Griswold, IA?

The median first fall frost near 51535 is October 14, giving a median frost-free growing season of 174 days.

When should I plant tomatoes in 51535?

Start tomato seeds indoors around Feb 26 – Mar 12 and set transplants outside around Apr 30 – May 14, one to three weeks after the median last frost.

How much rain and snow does 51535 get?

About 36.4 inches of precipitation a year and 28 inches of snowfall (NOAA 1991–2020 normals, Oakland station).

How hot do summers get in Griswold, IA?

The average high peaks at 85 °F in July, with about 20 days a year at 90 °F or more.

What kind of soil does 51535 have?

The USDA soil survey maps Nevin at the center of ZIP 51535: silty clay loam, somewhat poorly drained, pH about 6.2 (slightly acidic).

Did spring come early in Griswold, IA in 2026?

Spring leaf-out near 51535 came on Mar 15 in 2026, 17 days earlier than the 1991–2020 average (Apr 1), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Griswold, IA?

Long-day onions: the longest day near 51535 is 15 h 09 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 51535 change?

Yes. The 2012 USDA map put 51535 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.