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

Planting zone for 50241 — Saint Marys, IA

ZIP code 50241 (Saint Marys, Warren County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 24 and the first fall frost October 12.

Where ZIP 50241 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 24
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 Saint Marys, 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 Saint Marys, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 24median — 50% chance of a later frost
Safe for tender plantsMay 8only 10% chance of frost after
First fall frostOctober 12median — 10% chance by Sep 27
Growing season168 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 14 and returns around October 21.

From the NOAA station Indianola 2w, IA — 6 miles away, elevation 925 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 50241

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 13 – Mar 27
SpinachSow outdoors · Mar 13 – Apr 3
Broccoli, cabbageStart indoors · Feb 13 – Feb 27
Broccoli, cabbageTransplant · Apr 3 – Apr 17
Onion setsPlant outdoors · Mar 27 – Apr 10
PotatoesPlant outdoors · Apr 3 – Apr 17
LettuceSow outdoors · Mar 27 – Apr 10
Carrots, beetsSow outdoors · Apr 3 – Apr 17
TomatoesStart indoors · Feb 27 – Mar 13
TomatoesTransplant · May 1 – May 15
Peppers, eggplantStart indoors · Feb 13 – Feb 27
Peppers, eggplantTransplant · May 8 – May 22
BeansSow outdoors · May 1 – May 15
Sweet cornSow outdoors · May 1 – May 15
Cucumbers, squashSow outdoors · May 1 – May 15
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 24) 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 50241 came on Mar 15 — 18 days earlier than the 1991–2020 average (Apr 2).

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 Saint Marys, IA.

Soil in Saint Marys, IA

The soil mapped at the center of ZIP 50241 is Macksburg — silty clay loam, somewhat poorly drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH5.9moderately 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: Macksburg silty 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 50241; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Saint Marys, IA

Summer high86 °Faverage high, July
Winter low12 °Faverage low, January
Hot days18days a year at 90 °F or more
Freezing nights143nights a year at 32 °F or less
Growing degree days3,252base 50 °F — the season’s usable heat
Longest day15 h 10 mindaylight on June 21
Shortest day9 h 11 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation37.8 inper year, rain and melted snow
Snowfall31 inper year; 52 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 32 °F, low 12 °F 32°12° JanFebruary: average high 36 °F, low 15 °F 36°15° FebMarch: average high 50 °F, low 27 °F 50°27° MarApril: average high 62 °F, low 38 °F 62°38° AprMay: average high 72 °F, low 50 °F 72°50° MayJune: average high 81 °F, low 60 °F 81°60° JunJuly: average high 86 °F, low 64 °F 86°64° JulAugust: average high 84 °F, low 62 °F 84°62° AugSeptember: average high 78 °F, low 52 °F 78°52° SepOctober: average high 65 °F, low 40 °F 65°40° OctNovember: average high 50 °F, low 28 °F 50°28° NovDecember: average high 37 °F, low 17 °F 37°17° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″6″January: 0.91 in precipitation, 8.5 in snowfall 0.9❄9 JanFebruary: 1.42 in precipitation, 8.2 in snowfall 1.4❄8 FebMarch: 1.94 in precipitation, 3.7 in snowfall 1.9❄4 MarApril: 3.88 in precipitation, 1 in snowfall 3.9❄1 AprMay: 5.58 in precipitation, 0.3 in snowfall 5.6 MayJune: 5.72 in precipitation 5.7 JunJuly: 4.32 in precipitation 4.3 JulAugust: 3.90 in precipitation 3.9 AugSeptember: 3.86 in precipitation 3.9 SepOctober: 3.02 in precipitation, 0.5 in snowfall 3.0❄1 OctNovember: 1.85 in precipitation, 1.9 in snowfall 1.9❄2 NovDecember: 1.40 in precipitation, 6.7 in snowfall 1.4❄7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Indianola 2w, IA (6 mi away); precipitation: Indianola 2w, IA (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

502405b
Saint Charles, IA · 3 mi
501605b
Martensdale, IA · 5 mi
502295b
Prole, IA · 5 mi
502185b
Patterson, IA · 8 mi
501255b
Indianola, IA · 8 mi
502105b
New Virginia, IA · 8 mi
502115b
Norwalk, IA · 10 mi
502575b
Truro, IA · 11 mi

Iowa planting zones →

Questions about 50241

What planting zone is ZIP code 50241?

ZIP code 50241 (Saint Marys, 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 Saint Marys, IA?

The median last spring frost (32 °F) near 50241 is April 24; after May 8 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Indianola 2w station.

When is the first frost in Saint Marys, IA?

The median first fall frost near 50241 is October 12, giving a median frost-free growing season of 168 days.

When should I plant tomatoes in 50241?

Start tomato seeds indoors around Feb 27 – Mar 13 and set transplants outside around May 1 – May 15, one to three weeks after the median last frost.

How much rain and snow does 50241 get?

About 37.8 inches of precipitation a year and 31 inches of snowfall (NOAA 1991–2020 normals, Indianola 2w station).

How hot do summers get in Saint Marys, IA?

The average high peaks at 86 °F in July, with about 18 days a year at 90 °F or more.

What kind of soil does 50241 have?

The USDA soil survey maps Macksburg at the center of ZIP 50241: silty clay loam, somewhat poorly drained, pH about 5.9 (moderately acidic).

Did spring come early in Saint Marys, IA in 2026?

Spring leaf-out near 50241 came on Mar 15 in 2026, 18 days earlier than the 1991–2020 average (Apr 2), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Saint Marys, IA?

Long-day onions: the longest day near 50241 is 15 h 10 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 50241 change?

Yes. The 2012 USDA map put 50241 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.