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

Planting zone for 52594 — Unionville, IA

ZIP code 52594 (Unionville, Appanoose County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 18 and the first fall frost October 23.

Where ZIP 52594 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 18
First frostOct 23
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 Unionville, 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 Unionville, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 18median — 50% chance of a later frost
Safe for tender plantsMay 2only 10% chance of frost after
First fall frostOctober 23median — 10% chance by Oct 10
Growing season187 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 7 and returns around October 31.

From the NOAA station Rathbun Dam, IA — 12 miles away, elevation 965 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 52594

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 7 – Mar 21
SpinachSow outdoors · Mar 7 – Mar 28
Broccoli, cabbageStart indoors · Feb 7 – Feb 21
Broccoli, cabbageTransplant · Mar 28 – Apr 11
Onion setsPlant outdoors · Mar 21 – Apr 4
PotatoesPlant outdoors · Mar 28 – Apr 11
LettuceSow outdoors · Mar 21 – Apr 4
Carrots, beetsSow outdoors · Mar 28 – Apr 11
TomatoesStart indoors · Feb 21 – Mar 7
TomatoesTransplant · Apr 25 – May 9
Peppers, eggplantStart indoors · Feb 7 – Feb 21
Peppers, eggplantTransplant · May 2 – May 16
BeansSow outdoors · Apr 25 – May 9
Sweet cornSow outdoors · Apr 25 – May 9
Cucumbers, squashSow outdoors · Apr 25 – May 9
Fall lettuce, spinachSow outdoors · Aug 28 – Sep 11
GarlicPlant cloves · Oct 9 – Nov 13
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 18) and first fall frost (Oct 23) 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 52594 came on Mar 11 — 20 days earlier than the 1991–2020 average (Mar 31).

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 Unionville, IA.

Soil in Unionville, IA

The soil mapped at the center of ZIP 52594 is Lindley — loam, well drained.

TextureLoama good balance for most vegetables
pH5.5moderately acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2.5%moderate
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Lindley loam, 18 to 25 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 52594; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Unionville, IA

Summer high85 °Faverage high, July
Winter low13 °Faverage low, January
Hot days19days a year at 90 °F or more
Freezing nights136nights a year at 32 °F or less
Growing degree days3,337base 50 °F — the season’s usable heat
Longest day15 h 06 mindaylight on June 21
Shortest day9 h 14 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation38.6 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 13 °F 31°13° JanFebruary: average high 37 °F, low 16 °F 37°16° FebMarch: average high 50 °F, low 28 °F 50°28° MarApril: average high 62 °F, low 39 °F 62°39° AprMay: average high 71 °F, low 51 °F 71°51° MayJune: average high 81 °F, low 61 °F 81°61° JunJuly: average high 85 °F, low 66 °F 85°66° JulAugust: average high 84 °F, low 64 °F 84°64° AugSeptember: average high 77 °F, low 54 °F 77°54° SepOctober: average high 65 °F, low 42 °F 65°42° OctNovember: average high 50 °F, low 29 °F 50°29° NovDecember: average high 37 °F, low 19 °F 37°19° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 1.09 in precipitation 1.1 JanFebruary: 1.49 in precipitation 1.5 FebMarch: 2.03 in precipitation 2.0 MarApril: 3.93 in precipitation 3.9 AprMay: 5.36 in precipitation 5.4 MayJune: 5.24 in precipitation 5.2 JunJuly: 4.57 in precipitation 4.6 JulAugust: 4.62 in precipitation 4.6 AugSeptember: 3.81 in precipitation 3.8 SepOctober: 2.93 in precipitation 2.9 OctNovember: 2.04 in precipitation 2.0 NovDecember: 1.46 in precipitation 1.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Rathbun Dam, IA (12 mi away); precipitation: Rathbun Dam, IA (12 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

525525b
Drakesville, IA · 5 mi
525935b
Udell, IA · 7 mi
525365b
Blakesburg, IA · 9 mi
525715b
Moravia, IA · 10 mi
525725b
Moulton, IA · 12 mi
525375b
Bloomfield, IA · 14 mi
525315b
Albia, IA · 16 mi
525555b
Exline, IA · 16 mi

Iowa planting zones →

Questions about 52594

What planting zone is ZIP code 52594?

ZIP code 52594 (Unionville, 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 Unionville, IA?

The median last spring frost (32 °F) near 52594 is April 18; after May 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Rathbun Dam station.

When is the first frost in Unionville, IA?

The median first fall frost near 52594 is October 23, giving a median frost-free growing season of 187 days.

When should I plant tomatoes in 52594?

Start tomato seeds indoors around Feb 21 – Mar 7 and set transplants outside around Apr 25 – May 9, one to three weeks after the median last frost.

How much rain and snow does 52594 get?

About 38.6 inches of precipitation a year (NOAA 1991–2020 normals, Rathbun Dam station).

How hot do summers get in Unionville, IA?

The average high peaks at 85 °F in July, with about 19 days a year at 90 °F or more.

What kind of soil does 52594 have?

The USDA soil survey maps Lindley at the center of ZIP 52594: loam, well drained, pH about 5.5 (moderately acidic).

Did spring come early in Unionville, IA in 2026?

Spring leaf-out near 52594 came on Mar 11 in 2026, 20 days earlier than the 1991–2020 average (Mar 31), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Unionville, IA?

Long-day onions: the longest day near 52594 is 15 h 06 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).