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

Planting zone for 50450 — Lake Mills, IA

ZIP code 50450 (Lake Mills, Winnebago County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is April 30 and the first fall frost October 7.

Where ZIP 50450 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 30
First frostOct 7
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 Lake Mills, 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 Lake Mills, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 30median — 50% chance of a later frost
Safe for tender plantsMay 10only 10% chance of frost after
First fall frostOctober 7median — 10% chance by Sep 22
Growing season159 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 18 and returns around October 18.

From the NOAA station Forest City 2 Nne, IA — 11 miles away, elevation 1,280 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 50450

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 19 – Apr 2
SpinachSow outdoors · Mar 19 – Apr 9
Broccoli, cabbageStart indoors · Feb 19 – Mar 5
Broccoli, cabbageTransplant · Apr 9 – Apr 23
Onion setsPlant outdoors · Apr 2 – Apr 16
PotatoesPlant outdoors · Apr 9 – Apr 23
LettuceSow outdoors · Apr 2 – Apr 16
Carrots, beetsSow outdoors · Apr 9 – Apr 23
TomatoesStart indoors · Mar 5 – Mar 19
TomatoesTransplant · May 7 – May 21
Peppers, eggplantStart indoors · Feb 19 – Mar 5
Peppers, eggplantTransplant · May 14 – May 28
BeansSow outdoors · May 7 – May 21
Sweet cornSow outdoors · May 7 – May 21
Cucumbers, squashSow outdoors · May 7 – May 21
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 (Apr 30) 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 50450 came on Mar 30 — 16 days earlier than the 1991–2020 average (Apr 15).

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 Lake Mills, IA.

Soil in Lake Mills, IA

The soil mapped at the center of ZIP 50450 is Linder — loam, somewhat poorly drained.

TextureLoama good balance for most vegetables
pH6.7neutral; most vegetables like 6.0–7.0
DrainageSomewhat poorly drainedconsider raised beds
Organic matter4%moderate
Hydrologic groupB/Dmoderate when drained; wet otherwise
Farmland classprime farmlandUSDA classification

Map unit: Linder 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 50450; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Lake Mills, IA

Summer high81 °Faverage high, July
Winter low6 °Faverage low, January
Hot days9days a year at 90 °F or more
Freezing nights159nights a year at 32 °F or less
Growing degree days2,601base 50 °F — the season’s usable heat
Longest day15 h 25 mindaylight on June 21
Shortest day8 h 57 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation37.2 inper year, rain and melted snow
Snowfall38 inper year; 87 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 23 °F, low 6 °F 23°6° JanFebruary: average high 27 °F, low 10 °F 27°10° FebMarch: average high 40 °F, low 23 °F 40°23° MarApril: average high 56 °F, low 34 °F 56°34° AprMay: average high 69 °F, low 47 °F 69°47° MayJune: average high 78 °F, low 58 °F 78°58° JunJuly: average high 81 °F, low 62 °F 81°62° JulAugust: average high 79 °F, low 59 °F 79°59° AugSeptember: average high 73 °F, low 50 °F 73°50° SepOctober: average high 60 °F, low 37 °F 60°37° OctNovember: average high 43 °F, low 24 °F 43°24° NovDecember: average high 29 °F, low 13 °F 29°13° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″6″January: 1.07 in precipitation, 8.2 in snowfall 1.1❄8 JanFebruary: 1.14 in precipitation, 9.5 in snowfall 1.1❄10 FebMarch: 1.98 in precipitation, 5.5 in snowfall 2.0❄6 MarApril: 4.10 in precipitation, 2.8 in snowfall 4.1❄3 AprMay: 5.07 in precipitation 5.1 MayJune: 5.69 in precipitation 5.7 JunJuly: 4.70 in precipitation 4.7 JulAugust: 4.25 in precipitation 4.3 AugSeptember: 3.39 in precipitation 3.4 SepOctober: 2.56 in precipitation, 0.3 in snowfall 2.6 OctNovember: 1.80 in precipitation, 3.1 in snowfall 1.8❄3 NovDecember: 1.41 in precipitation, 8.7 in snowfall 1.4❄9 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Forest City 2 Nne, IA (11 mi away); precipitation: Lake Mills, IA (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

560295a
Emmons, MN · 7 mi
504465a
Joice, IA · 7 mi
504535a
Leland, IA · 7 mi
504735a
Scarville, IA · 8 mi
560895a
Twin Lakes, MN · 11 mi
504445a
Hanlontown, IA · 11 mi
504345a
Fertile, IA · 12 mi
560515a
Kiester, MN · 12 mi

Iowa planting zones →

Questions about 50450

What planting zone is ZIP code 50450?

ZIP code 50450 (Lake Mills, 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 Lake Mills, IA?

The median last spring frost (32 °F) near 50450 is April 30; after May 10 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Forest City 2 Nne station.

When is the first frost in Lake Mills, IA?

The median first fall frost near 50450 is October 7, giving a median frost-free growing season of 159 days.

When should I plant tomatoes in 50450?

Start tomato seeds indoors around Mar 5 – Mar 19 and set transplants outside around May 7 – May 21, one to three weeks after the median last frost.

How much rain and snow does 50450 get?

About 37.2 inches of precipitation a year and 38 inches of snowfall (NOAA 1991–2020 normals, Lake Mills station).

How hot do summers get in Lake Mills, IA?

The average high peaks at 81 °F in July, with about 9 days a year at 90 °F or more.

What kind of soil does 50450 have?

The USDA soil survey maps Linder at the center of ZIP 50450: loam, somewhat poorly drained, pH about 6.7 (neutral).

Did spring come early in Lake Mills, IA in 2026?

Spring leaf-out near 50450 came on Mar 30 in 2026, 16 days earlier than the 1991–2020 average (Apr 15), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Lake Mills, IA?

Long-day onions: the longest day near 50450 is 15 h 25 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).