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

Planting zone for 51346 — Hartley, IA

ZIP code 51346 (Hartley, O'Brien County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 1 and the first fall frost October 7.

Where ZIP 51346 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.

Zone5a−20 to −15 °F
Coldest night−28.9 to −26.1 °C
Last frostMay 1
First frostOct 7
2012 zone4b

Was 4b 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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Hartley, 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 Hartley, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 1median — 50% chance of a later frost
Safe for tender plantsMay 13only 10% chance of frost after
First fall frostOctober 7median — 10% chance by Sep 23
Growing season160 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 20 and returns around October 17.

From the NOAA station Sanborn, IA — 11 miles away, elevation 1,552 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 51346

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 20 – Apr 3
SpinachSow outdoors · Mar 20 – Apr 10
Broccoli, cabbageStart indoors · Feb 20 – Mar 6
Broccoli, cabbageTransplant · Apr 10 – Apr 24
Onion setsPlant outdoors · Apr 3 – Apr 17
PotatoesPlant outdoors · Apr 10 – Apr 24
LettuceSow outdoors · Apr 3 – Apr 17
Carrots, beetsSow outdoors · Apr 10 – Apr 24
TomatoesStart indoors · Mar 6 – Mar 20
TomatoesTransplant · May 8 – May 22
Peppers, eggplantStart indoors · Feb 20 – Mar 6
Peppers, eggplantTransplant · May 15 – May 29
BeansSow outdoors · May 8 – May 22
Sweet cornSow outdoors · May 8 – May 22
Cucumbers, squashSow outdoors · May 8 – May 22
Fall lettuce, spinachSow outdoors · Aug 12 – Aug 26
GarlicPlant cloves · Sep 23 – Oct 28
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 1) and first fall frost (Oct 7) 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 51346 came on Mar 25 — 20 days earlier than the 1991–2020 average (Apr 14).

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 5a in Iowa

461 plants native to the lower 48 states, recorded in Iowa, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. Each links to its USDA PLANTS profile.

Trees 46

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 185

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 133

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 Hartley, IA.

Soil in Hartley, IA

The soil mapped at the center of ZIP 51346 is Primghar — silty clay loam, somewhat poorly drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH6.5neutral; most vegetables like 6.0–7.0
DrainageSomewhat poorly drainedconsider raised beds
Organic matter6.2%high
Hydrologic groupC/Dslow when drained; wet otherwise
Farmland classprime farmlandUSDA classification

Map unit: Primghar 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 51346; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Hartley, IA

Summer high83 °Faverage high, July
Winter low6 °Faverage low, January
Hot days9days a year at 90 °F or more
Freezing nights166nights a year at 32 °F or less
Growing degree days2,694base 50 °F — the season’s usable heat
Longest day15 h 23 mindaylight on June 21
Shortest day8 h 59 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation30.8 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 24 °F, low 6 °F 24°6° JanFebruary: average high 28 °F, low 10 °F 28°10° FebMarch: average high 42 °F, low 22 °F 42°22° MarApril: average high 57 °F, low 34 °F 57°34° AprMay: average high 69 °F, low 47 °F 69°47° MayJune: average high 79 °F, low 58 °F 79°58° JunJuly: average high 83 °F, low 62 °F 83°62° JulAugust: average high 80 °F, low 60 °F 80°60° AugSeptember: average high 74 °F, low 50 °F 74°50° SepOctober: average high 60 °F, low 37 °F 60°37° OctNovember: average high 43 °F, low 23 °F 43°23° NovDecember: average high 29 °F, low 12 °F 29°12° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 0.77 in precipitation 0.8 JanFebruary: 0.78 in precipitation 0.8 FebMarch: 1.67 in precipitation 1.7 MarApril: 3.26 in precipitation 3.3 AprMay: 4.31 in precipitation 4.3 MayJune: 4.73 in precipitation 4.7 JunJuly: 3.62 in precipitation 3.6 JulAugust: 3.59 in precipitation 3.6 AugSeptember: 3.31 in precipitation 3.3 SepOctober: 2.39 in precipitation 2.4 OctNovember: 1.36 in precipitation 1.4 NovDecember: 0.97 in precipitation 1.0 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Sanborn, IA (11 mi away); precipitation: Everly 3 Wnw, IA (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

513385a
Everly, IA · 7 mi
512485a
Sanborn, IA · 10 mi
512455a
Primghar, IA · 11 mi
513505a
Melvin, IA · 11 mi
513575a
Royal, IA · 12 mi
510585a
Sutherland, IA · 14 mi
513405a
Fostoria, IA · 15 mi
513015a
Spencer, IA · 16 mi

Iowa planting zones →

Questions about 51346

What planting zone is ZIP code 51346?

ZIP code 51346 (Hartley, IA) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Hartley, IA?

The median last spring frost (32 °F) near 51346 is May 1; after May 13 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Sanborn station.

When is the first frost in Hartley, IA?

The median first fall frost near 51346 is October 7, giving a median frost-free growing season of 160 days.

When should I plant tomatoes in 51346?

Start tomato seeds indoors around Mar 6 – Mar 20 and set transplants outside around May 8 – May 22, one to three weeks after the median last frost.

How much rain and snow does 51346 get?

About 30.8 inches of precipitation a year (NOAA 1991–2020 normals, Everly 3 Wnw station).

How hot do summers get in Hartley, IA?

The average high peaks at 83 °F in July, with about 9 days a year at 90 °F or more.

What kind of soil does 51346 have?

The USDA soil survey maps Primghar at the center of ZIP 51346: silty clay loam, somewhat poorly drained, pH about 6.5 (neutral).

Did spring come early in Hartley, IA in 2026?

Spring leaf-out near 51346 came on Mar 25 in 2026, 20 days earlier than the 1991–2020 average (Apr 14), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Hartley, IA?

Long-day onions: the longest day near 51346 is 15 h 23 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 51346 change?

Yes. The 2012 USDA map put 51346 in zone 4b; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.