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

Planting zone for 50548 — Humboldt, IA

ZIP code 50548 (Humboldt, Humboldt County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is April 27 and the first fall frost October 9.

Where ZIP 50548 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 frostApr 27
First frostOct 9
2012 zone5a

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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Humboldt, 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 Humboldt, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 27median — 50% chance of a later frost
Safe for tender plantsMay 7only 10% chance of frost after
First fall frostOctober 9median — 10% chance by Sep 24
Growing season166 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 17 and returns around October 22.

From the NOAA station Humboldt Wtp, IA — within 1 mile, elevation 1,099 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 50548

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 16 – Mar 30
SpinachSow outdoors · Mar 16 – Apr 6
Broccoli, cabbageStart indoors · Feb 16 – Mar 2
Broccoli, cabbageTransplant · Apr 6 – Apr 20
Onion setsPlant outdoors · Mar 30 – Apr 13
PotatoesPlant outdoors · Apr 6 – Apr 20
LettuceSow outdoors · Mar 30 – Apr 13
Carrots, beetsSow outdoors · Apr 6 – Apr 20
TomatoesStart indoors · Mar 2 – Mar 16
TomatoesTransplant · May 4 – May 18
Peppers, eggplantStart indoors · Feb 16 – Mar 2
Peppers, eggplantTransplant · May 11 – May 25
BeansSow outdoors · May 4 – May 18
Sweet cornSow outdoors · May 4 – May 18
Cucumbers, squashSow outdoors · May 4 – May 18
Fall lettuce, spinachSow outdoors · Aug 14 – Aug 28
GarlicPlant cloves · Sep 25 – Oct 30
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 27) and first fall frost (Oct 9) 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 50548 came on Mar 25 — 17 days earlier than the 1991–2020 average (Apr 11).

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 Humboldt, IA.

Soil in Humboldt, IA

The soil mapped at the center of ZIP 50548 is Lester — loam, well drained.

TextureLoama good balance for most vegetables
pH6.6neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3%moderate
Hydrologic groupCwater soaks in slowly
Farmland classFarmland of statewide importanceUSDA classification

Map unit: Lester loam, 6 to 10 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 50548; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Humboldt, IA

Summer high81 °Faverage high, July
Winter low9 °Faverage low, January
Hot days6days a year at 90 °F or more
Freezing nights152nights a year at 32 °F or less
Growing degree days2,705base 50 °F — the season’s usable heat
Longest day15 h 20 mindaylight on June 21
Shortest day9 h 02 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation35 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 9 °F 24°9° JanFebruary: average high 29 °F, low 12 °F 29°12° FebMarch: average high 43 °F, low 25 °F 43°25° MarApril: average high 57 °F, low 36 °F 57°36° AprMay: average high 68 °F, low 49 °F 68°49° MayJune: average high 78 °F, low 59 °F 78°59° JunJuly: average high 81 °F, low 63 °F 81°63° JulAugust: average high 79 °F, low 60 °F 79°60° AugSeptember: average high 73 °F, low 51 °F 73°51° SepOctober: average high 60 °F, low 39 °F 60°39° OctNovember: average high 43 °F, low 26 °F 43°26° NovDecember: average high 30 °F, low 15 °F 30°15° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 0.91 in precipitation 0.9 JanFebruary: 1.04 in precipitation 1.0 FebMarch: 2.02 in precipitation 2.0 MarApril: 3.30 in precipitation 3.3 AprMay: 4.80 in precipitation 4.8 MayJune: 5.48 in precipitation 5.5 JunJuly: 4.15 in precipitation 4.2 JulAugust: 4.55 in precipitation 4.5 AugSeptember: 3.33 in precipitation 3.3 SepOctober: 2.45 in precipitation 2.5 OctNovember: 1.61 in precipitation 1.6 NovDecember: 1.32 in precipitation 1.3 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Humboldt Wtp, IA (within 1 mile); precipitation: Humboldt Wtp, IA (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

505295a
Dakota City, IA · 1 mi
505825a
Rutland, IA · 7 mi
505165a
Badger, IA · 8 mi
505915a
Thor, IA · 9 mi
505455a
Hardy, IA · 9 mi
505585a
Livermore, IA · 11 mi
505245a
Clare, IA · 11 mi
505205a
Bradgate, IA · 11 mi

Iowa planting zones →

Questions about 50548

What planting zone is ZIP code 50548?

ZIP code 50548 (Humboldt, 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 Humboldt, IA?

The median last spring frost (32 °F) near 50548 is April 27; after May 7 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Humboldt Wtp station.

When is the first frost in Humboldt, IA?

The median first fall frost near 50548 is October 9, giving a median frost-free growing season of 166 days.

When should I plant tomatoes in 50548?

Start tomato seeds indoors around Mar 2 – Mar 16 and set transplants outside around May 4 – May 18, one to three weeks after the median last frost.

How much rain and snow does 50548 get?

About 35 inches of precipitation a year (NOAA 1991–2020 normals, Humboldt Wtp station).

How hot do summers get in Humboldt, IA?

The average high peaks at 81 °F in July, with about 6 days a year at 90 °F or more.

What kind of soil does 50548 have?

The USDA soil survey maps Lester at the center of ZIP 50548: loam, well drained, pH about 6.6 (neutral).

Did spring come early in Humboldt, IA in 2026?

Spring leaf-out near 50548 came on Mar 25 in 2026, 17 days earlier than the 1991–2020 average (Apr 11), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Humboldt, IA?

Long-day onions: the longest day near 50548 is 15 h 20 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).