Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 50129 — Jefferson, IA

ZIP code 50129 (Jefferson, Greene County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 26 and the first fall frost October 9.

Where ZIP 50129 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 26

First frostOct 9

2012 zone5a

Was 5a 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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Jefferson, 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 Jefferson, IA

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostApril 26median — 50% chance of a later frost

Safe for tender plantsMay 8only 10% chance of frost after

First fall frostOctober 9median — 10% chance by Sep 23

Growing season164 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 15 and returns around October 21.

From the NOAA station Jefferson, IA — within 1 mile, elevation 1,056 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 50129

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 15 – Mar 29

SpinachSow outdoors · Mar 15 – Apr 5

Broccoli, cabbageStart indoors · Feb 15 – Mar 1

Broccoli, cabbageTransplant · Apr 5 – Apr 19

Onion setsPlant outdoors · Mar 29 – Apr 12

PotatoesPlant outdoors · Apr 5 – Apr 19

LettuceSow outdoors · Mar 29 – Apr 12

Carrots, beetsSow outdoors · Apr 5 – Apr 19

TomatoesStart indoors · Mar 1 – Mar 15

TomatoesTransplant · May 3 – May 17

Peppers, eggplantStart indoors · Feb 15 – Mar 1

Peppers, eggplantTransplant · May 10 – May 24

BeansSow outdoors · May 3 – May 17

Sweet cornSow outdoors · May 3 – May 17

Cucumbers, squashSow outdoors · May 3 – May 17

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 26) 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 50129 came on Mar 24 — 13 days earlier than the 1991–2020 average (Apr 6).

average
Apr 62026
Mar 24

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.

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 Jefferson, IA.

Soil in Jefferson, IA

The soil mapped at the center of ZIP 50129 is Nicollet — loam, somewhat poorly drained.

TextureLoama good balance for most vegetables

pH6.2slightly acidic; most vegetables like 6.0–7.0

DrainageSomewhat poorly drainedconsider raised beds

Organic matter6%high

Hydrologic groupB/Dmoderate when drained; wet otherwise

Farmland classprime farmlandUSDA classification

Map unit: Nicollet loam, 1 to 3 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 50129; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Jefferson, IA

Summer high83 °Faverage high, July

Winter low9 °Faverage low, January

Hot days19days a year at 90 °F or more

Freezing nights149nights a year at 32 °F or less

Growing degree days2,966base 50 °F — the season’s usable heat

Longest day15 h 15 mindaylight on June 21

Shortest day9 h 07 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation35.3 inper year, rain and melted snow

Snowfall32 inper year; 61 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

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

Nearby ZIP codes

8 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

501075a

Grand Junction, IA · 8 mi

Iowa planting zones →

Questions about 50129

What planting zone is ZIP code 50129?

ZIP code 50129 (Jefferson, 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 Jefferson, IA?

The median last spring frost (32 °F) near 50129 is April 26; after May 8 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Jefferson station.

When is the first frost in Jefferson, IA?

The median first fall frost near 50129 is October 9, giving a median frost-free growing season of 164 days.

When should I plant tomatoes in 50129?

Start tomato seeds indoors around Mar 1 – Mar 15 and set transplants outside around May 3 – May 17, one to three weeks after the median last frost.

How much rain and snow does 50129 get?

About 35.3 inches of precipitation a year and 32 inches of snowfall (NOAA 1991–2020 normals, Jefferson station).

How hot do summers get in Jefferson, IA?

The average high peaks at 83 °F in July, with about 19 days a year at 90 °F or more.

What kind of soil does 50129 have?

The USDA soil survey maps Nicollet at the center of ZIP 50129: loam, somewhat poorly drained, pH about 6.2 (slightly acidic).

Did spring come early in Jefferson, IA in 2026?

Spring leaf-out near 50129 came on Mar 24 in 2026, 13 days earlier than the 1991–2020 average (Apr 6), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Jefferson, IA?

Long-day onions: the longest day near 50129 is 15 h 15 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 50129 change?

Yes. The 2012 USDA map put 50129 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.