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

Planting zone for 51010 — Castana, IA

ZIP code 51010 (Castana, Monona County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 25 and the first fall frost October 12.

Where ZIP 51010 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 25
First frostOct 12
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 Castana, 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 Castana, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 25median — 50% chance of a later frost
Safe for tender plantsMay 7only 10% chance of frost after
First fall frostOctober 12median — 10% chance by Sep 28
Growing season170 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 15 and returns around October 23.

From the NOAA station Castana Exp Farm, IA — 6 miles away, elevation 1,401 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 51010

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 14 – Mar 28
SpinachSow outdoors · Mar 14 – Apr 4
Broccoli, cabbageStart indoors · Feb 14 – Feb 28
Broccoli, cabbageTransplant · Apr 4 – Apr 18
Onion setsPlant outdoors · Mar 28 – Apr 11
PotatoesPlant outdoors · Apr 4 – Apr 18
LettuceSow outdoors · Mar 28 – Apr 11
Carrots, beetsSow outdoors · Apr 4 – Apr 18
TomatoesStart indoors · Feb 28 – Mar 14
TomatoesTransplant · May 2 – May 16
Peppers, eggplantStart indoors · Feb 14 – Feb 28
Peppers, eggplantTransplant · May 9 – May 23
BeansSow outdoors · May 2 – May 16
Sweet cornSow outdoors · May 2 – May 16
Cucumbers, squashSow outdoors · May 2 – May 16
Fall lettuce, spinachSow outdoors · Aug 17 – Aug 31
GarlicPlant cloves · Sep 28 – Nov 2
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 25) and first fall frost (Oct 12) 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 51010 came on Mar 20 — 16 days earlier than the 1991–2020 average (Apr 5).

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 Castana, IA.

Soil in Castana, IA

The soil mapped at the center of ZIP 51010 is Napier — silt loam, well drained.

TextureSilt loama good balance for most vegetables
pH6.7neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3.5%moderate
Hydrologic groupBwater soaks in moderately
Farmland classFarmland of statewide importanceUSDA classification

Map unit: Napier silt 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 51010; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Castana, IA

Summer high84 °Faverage high, July
Winter low10 °Faverage low, January
Hot days13days a year at 90 °F or more
Freezing nights144nights a year at 32 °F or less
Growing degree days3,036base 50 °F — the season’s usable heat
Longest day15 h 15 mindaylight on June 21
Shortest day9 h 06 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation31.6 inper year, rain and melted snow
Snowfall24 inper year; 48 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 29 °F, low 10 °F 29°10° JanFebruary: average high 33 °F, low 14 °F 33°14° FebMarch: average high 47 °F, low 26 °F 47°26° MarApril: average high 60 °F, low 37 °F 60°37° AprMay: average high 71 °F, low 49 °F 71°49° MayJune: average high 80 °F, low 60 °F 80°60° JunJuly: average high 84 °F, low 64 °F 84°64° JulAugust: average high 82 °F, low 61 °F 82°61° AugSeptember: average high 75 °F, low 53 °F 75°53° SepOctober: average high 63 °F, low 40 °F 63°40° OctNovember: average high 47 °F, low 26 °F 47°26° NovDecember: average high 33 °F, low 16 °F 33°16° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″January: 0.72 in precipitation, 5.7 in snowfall 0.7❄6 JanFebruary: 1.01 in precipitation, 4.9 in snowfall 1.0❄5 FebMarch: 1.73 in precipitation, 3.4 in snowfall 1.7❄3 MarApril: 3.59 in precipitation, 1.6 in snowfall 3.6❄2 AprMay: 4.85 in precipitation 4.8 MayJune: 4.45 in precipitation 4.5 JunJuly: 3.47 in precipitation 3.5 JulAugust: 3.82 in precipitation 3.8 AugSeptember: 3.14 in precipitation 3.1 SepOctober: 2.32 in precipitation, 0.5 in snowfall 2.3❄1 OctNovember: 1.33 in precipitation, 0.9 in snowfall 1.3❄1 NovDecember: 1.14 in precipitation, 6.9 in snowfall 1.1❄7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Castana Exp Farm, IA (6 mi away); precipitation: Kennebec, IA (3 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

510515a
Rodney, IA · 8 mi
510405a
Onawa, IA · 8 mi
510345a
Mapleton, IA · 9 mi
510565a
Smithland, IA · 10 mi
515725b
Soldier, IA · 10 mi
510265a
Hornick, IA · 13 mi
515585b
Moorhead, IA · 13 mi
510635a
Whiting, IA · 13 mi

Iowa planting zones →

Questions about 51010

What planting zone is ZIP code 51010?

ZIP code 51010 (Castana, 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 Castana, IA?

The median last spring frost (32 °F) near 51010 is April 25; after May 7 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Castana Exp Farm station.

When is the first frost in Castana, IA?

The median first fall frost near 51010 is October 12, giving a median frost-free growing season of 170 days.

When should I plant tomatoes in 51010?

Start tomato seeds indoors around Feb 28 – Mar 14 and set transplants outside around May 2 – May 16, one to three weeks after the median last frost.

How much rain and snow does 51010 get?

About 31.6 inches of precipitation a year and 24 inches of snowfall (NOAA 1991–2020 normals, Kennebec station).

How hot do summers get in Castana, IA?

The average high peaks at 84 °F in July, with about 13 days a year at 90 °F or more.

What kind of soil does 51010 have?

The USDA soil survey maps Napier at the center of ZIP 51010: silt loam, well drained, pH about 6.7 (neutral).

Did spring come early in Castana, IA in 2026?

Spring leaf-out near 51010 came on Mar 20 in 2026, 16 days earlier than the 1991–2020 average (Apr 5), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Castana, IA?

Long-day onions: the longest day near 51010 is 15 h 15 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 51010 change?

Yes. The 2012 USDA map put 51010 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.