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

Planting zone for Mason City, IA

Mason City, IA is in USDA zone 5a across its 2 ZIP codes. The median last spring frost is April 29 and the first fall frost October 7.

Mason City on the zone map

Outlined: its 1 ZIP code areas · 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
ZIP codes2
Last frostApr 29
First frostOct 7
Growing season161 days

5a 2 ZIPs

Frost forecast — next 7 nights

live from the National Weather Service

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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 Mason City, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 29median — 50% chance of a later frost
Safe for tender plantsMay 9only 10% chance of frost after
First fall frostOctober 7median — 10% chance by Sep 25
Growing season161 daysfrost-free, median

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

From the NOAA station Mason City, IA, elevation 1,106 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 Mason City

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 18 – Apr 1
SpinachSow outdoors · Mar 18 – Apr 8
Broccoli, cabbageStart indoors · Feb 18 – Mar 4
Broccoli, cabbageTransplant · Apr 8 – Apr 22
Onion setsPlant outdoors · Apr 1 – Apr 15
PotatoesPlant outdoors · Apr 8 – Apr 22
LettuceSow outdoors · Apr 1 – Apr 15
Carrots, beetsSow outdoors · Apr 8 – Apr 22
TomatoesStart indoors · Mar 4 – Mar 18
TomatoesTransplant · May 6 – May 20
Peppers, eggplantStart indoors · Feb 18 – Mar 4
Peppers, eggplantTransplant · May 13 – May 27
BeansSow outdoors · May 6 – May 20
Sweet cornSow outdoors · May 6 – May 20
Cucumbers, squashSow outdoors · May 6 – May 20
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 29) 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 50401 came on Mar 28 — 17 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 Mason City, IA.

Soil in Mason City, IA

The soil mapped at the center of ZIP 50401 is Anthroportic Udorthents — loam, moderately well drained.

TextureLoama good balance for most vegetables
pH6.3slightly acidic; most vegetables like 6.0–7.0
DrainageModerately well drainednatural drainage class
Organic matter1%low — add compost
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Anthroportic Udorthents, 2 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 50401; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mason City, IA

Summer high82 °Faverage high, July
Winter low7 °Faverage low, January
Hot days9days a year at 90 °F or more
Freezing nights161nights a year at 32 °F or less
Growing degree days2,638base 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)
Precipitation37.7 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 7 °F 24°7° JanFebruary: average high 29 °F, low 11 °F 29°11° FebMarch: average high 41 °F, low 23 °F 41°23° MarApril: average high 56 °F, low 35 °F 56°35° AprMay: average high 69 °F, low 47 °F 69°47° MayJune: average high 79 °F, low 58 °F 79°58° JunJuly: average high 82 °F, low 62 °F 82°62° JulAugust: average high 80 °F, low 59 °F 80°59° AugSeptember: average high 74 °F, low 50 °F 74°50° SepOctober: average high 60 °F, low 38 °F 60°38° OctNovember: average high 43 °F, low 25 °F 43°25° NovDecember: average high 30 °F, low 14 °F 30°14° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 0.92 in precipitation 0.9 JanFebruary: 1.30 in precipitation 1.3 FebMarch: 2.21 in precipitation 2.2 MarApril: 4.30 in precipitation 4.3 AprMay: 5.47 in precipitation 5.5 MayJune: 5.72 in precipitation 5.7 JunJuly: 4.69 in precipitation 4.7 JulAugust: 3.74 in precipitation 3.7 AugSeptember: 3.32 in precipitation 3.3 SepOctober: 2.74 in precipitation 2.7 OctNovember: 1.88 in precipitation 1.9 NovDecember: 1.42 in precipitation 1.4 Dec

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

ZIP codes in Mason City

504015a
−20 to −15 °F
504025a
−20 to −15 °F

Iowa planting zones →

Questions about Mason City

What planting zone is Mason City, IA?

Mason City, IA is in USDA hardiness zone 5a on the 2023 map (5a: −20 to −15 °F).

When is the last frost in Mason City, IA?

The median last spring frost is April 29 and the median first fall frost is October 7 (NOAA 1991–2020 normals, Mason City station).

When can I plant a garden in Mason City, IA?

Cool-season crops like peas and spinach go in around Mar 18 – Apr 8; tomatoes, peppers, beans and squash after about May 6, once frost risk has passed.

What kind of onions grow in Mason City, IA?

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

How much rain and snow does Mason City, IA get?

About 37.7 inches of precipitation a year (NOAA 1991–2020 normals).