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

Planting zone for 52577 — Oskaloosa, IA

ZIP code 52577 (Oskaloosa, Mahaska County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 21 and the first fall frost October 16.

Where ZIP 52577 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 21
First frostOct 16
2012 zone5b

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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Oskaloosa, 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 Oskaloosa, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 21median — 50% chance of a later frost
Safe for tender plantsMay 4only 10% chance of frost after
First fall frostOctober 16median — 10% chance by Sep 29
Growing season176 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 11 and returns around October 27.

From the NOAA station Oskaloosa, IA — 4 miles away, elevation 830 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 52577

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 10 – Mar 24
SpinachSow outdoors · Mar 10 – Mar 31
Broccoli, cabbageStart indoors · Feb 10 – Feb 24
Broccoli, cabbageTransplant · Mar 31 – Apr 14
Onion setsPlant outdoors · Mar 24 – Apr 7
PotatoesPlant outdoors · Mar 31 – Apr 14
LettuceSow outdoors · Mar 24 – Apr 7
Carrots, beetsSow outdoors · Mar 31 – Apr 14
TomatoesStart indoors · Feb 24 – Mar 10
TomatoesTransplant · Apr 28 – May 12
Peppers, eggplantStart indoors · Feb 10 – Feb 24
Peppers, eggplantTransplant · May 5 – May 19
BeansSow outdoors · Apr 28 – May 12
Sweet cornSow outdoors · Apr 28 – May 12
Cucumbers, squashSow outdoors · Apr 28 – May 12
Fall lettuce, spinachSow outdoors · Aug 21 – Sep 4
GarlicPlant cloves · Oct 2 – Nov 6
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 21) and first fall frost (Oct 16) 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 52577 came on Mar 16 — 17 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 Oskaloosa, IA.

Soil in Oskaloosa, IA

The soil mapped at the center of ZIP 52577 is Otley — silty clay loam, moderately well drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH6.0slightly acidic; most vegetables like 6.0–7.0
DrainageModerately well drainednatural drainage class
Organic matter3.5%moderate
Hydrologic groupCwater soaks in slowly
Farmland classFarmland of statewide importanceUSDA classification

Map unit: Otley silty clay 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 52577; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Oskaloosa, IA

Summer high86 °Faverage high, July
Winter low12 °Faverage low, January
Hot days15days a year at 90 °F or more
Freezing nights144nights a year at 32 °F or less
Growing degree days3,296base 50 °F — the season’s usable heat
Longest day15 h 09 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)
Precipitation38.7 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 31 °F, low 12 °F 31°12° JanFebruary: average high 36 °F, low 16 °F 36°16° FebMarch: average high 49 °F, low 27 °F 49°27° MarApril: average high 62 °F, low 38 °F 62°38° AprMay: average high 72 °F, low 51 °F 72°51° MayJune: average high 82 °F, low 61 °F 82°61° JunJuly: average high 86 °F, low 65 °F 86°65° JulAugust: average high 84 °F, low 62 °F 84°62° AugSeptember: average high 77 °F, low 53 °F 77°53° SepOctober: average high 65 °F, low 41 °F 65°41° OctNovember: average high 49 °F, low 29 °F 49°29° NovDecember: average high 36 °F, low 18 °F 36°18° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 1.75 in precipitation 1.8 JanFebruary: 1.74 in precipitation 1.7 FebMarch: 2.15 in precipitation 2.1 MarApril: 3.92 in precipitation 3.9 AprMay: 4.71 in precipitation 4.7 MayJune: 5.18 in precipitation 5.2 JunJuly: 4.40 in precipitation 4.4 JulAugust: 5.08 in precipitation 5.1 AugSeptember: 3.56 in precipitation 3.6 SepOctober: 2.68 in precipitation 2.7 OctNovember: 2.20 in precipitation 2.2 NovDecember: 1.35 in precipitation 1.4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Oskaloosa, IA (4 mi away); precipitation: Oskaloosa, IA (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

525345b
Beacon, IA · <1 mi
525955b
University Park, IA · 3 mi
525535b
Eddyville, IA · 9 mi
501435b
Leighton, IA · 9 mi
525435b
Cedar, IA · 9 mi
502075b
New Sharon, IA · 11 mi
525615b
Fremont, IA · 12 mi
525865b
Rose Hill, IA · 12 mi

Iowa planting zones →

Questions about 52577

What planting zone is ZIP code 52577?

ZIP code 52577 (Oskaloosa, 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 Oskaloosa, IA?

The median last spring frost (32 °F) near 52577 is April 21; after May 4 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Oskaloosa station.

When is the first frost in Oskaloosa, IA?

The median first fall frost near 52577 is October 16, giving a median frost-free growing season of 176 days.

When should I plant tomatoes in 52577?

Start tomato seeds indoors around Feb 24 – Mar 10 and set transplants outside around Apr 28 – May 12, one to three weeks after the median last frost.

How much rain and snow does 52577 get?

About 38.7 inches of precipitation a year (NOAA 1991–2020 normals, Oskaloosa station).

How hot do summers get in Oskaloosa, IA?

The average high peaks at 86 °F in July, with about 15 days a year at 90 °F or more.

What kind of soil does 52577 have?

The USDA soil survey maps Otley at the center of ZIP 52577: silty clay loam, moderately well drained, pH about 6.0 (slightly acidic).

Did spring come early in Oskaloosa, IA in 2026?

Spring leaf-out near 52577 came on Mar 16 in 2026, 17 days earlier than the 1991–2020 average (Apr 2), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Oskaloosa, IA?

Long-day onions: the longest day near 52577 is 15 h 09 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).