Decatur County, in Iowa, sits in USDA hardiness zone 5b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
A short list that earns its place here — sweet corn, tomato, apple, and hosta — with any one site's soil, sun, and drainage making the final cut.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Decatur County holds more than one microclimate.
Soils and elevations shift across Decatur County, so your frost dates and drainage aren't the county average. Enter your address and we'll score 1,112 plants against your land's actual soil, sun, and frost.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Quick Facts
USDA Zones
5b
Last Hard Freeze (28°F)
Mar 25
County normal — light frosts run a few weeks later
First Hard Freeze (28°F)
Nov 12
County normal — light frosts arrive a few weeks earlier
County Area
340K acres
Hardiness Zone Range
Zone maps are averages across Decatur County. Your yard's slope, trees, and frost pockets shift what actually grows — see your land's exact reading.
Soil in Decatur County
Across Decatur County, the ground is predominantly Alfisols, where Gara, Lindley, and Armstrong are the most extensive named soil series. The soil is generally somewhat poorly drained with a clay loam surface. Topsoil pH runs about 6.0–6.5, slightly acidic. Rainfall drains through hydrologic group D soils.
Soil order
Alfisols
Drainage
Somewhat poorly drained
Prime farmland
11%
Hydric soils
19%
Soil still varies lot by lot — soil types explained.
What Grows in Decatur County
Plants matched to Decatur County's USDA zones 5b — each links to its full growing profile.
Is it too late to plant in Decatur County?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Feb 25; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 25 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 12 — long-season crops need about 90 days of runway, quick greens only 30. Here the season winds down slowly: late sowings, a real autumn harvest, and garlic in the ground before the first hard freeze.
Growing Challenges in Iowa
What an experienced grower plans around here — each one has a move.
Cold winters reaching -20F or below
Choose perennials rated a zone hardier than yours — Iowa winters test the margins, and the margin is where plants are lost.
Variable spring weather delays planting
Let soil temperature and your local frost normal call the start, not the calendar — a two-week wait beats a replant.
Wind exposure on open prairies desiccates plants
Even a simple windbreak — a shrub row, a snow fence, a tall cover crop — cuts wind desiccation dramatically.
For cultivar selection, pest pressure, and planting-time guidance specific to Iowa, the Iowa State University Extension and Outreach is the authoritative local source.
Safe to Grow Here?
What the federal record shows across Decatur County — and how to grow with it.
We checked the federal record across Decatur County — 87 documented sites across 4 of the 9 source types we track.
The most significant on record: 11 brownfield sites. Former commercial or industrial land where legacy contamination may persist.
The federal record across Decatur County is a modest one — a typical footprint for a growing area. Nothing here calls for alarm; it's worth knowing which recorded sites sit closest to where you grow, and each one on the map carries its type and location. If one turns out to be a near neighbor, a one-time soil test settles the question.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Environmental Intelligence
Understanding what's nearby helps you make informed decisions about where and how to grow.
Sources Checked
across Decatur County
Severity Distribution
across Decatur County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Decatur County, Nitrate runs higher than the national average — 24 sites nearby. That's not a problem with your land — it's information about it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Decatur County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,112 plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Your Specific Parcel Matters
Decatur County Average
- ●USDA Zones 5b
- ●Generic soil type for the area
- ●State-average frost dates
YOUR Parcel
- ✓Your exact hardiness zone
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Decatur County
Pull a site-specific report for your exact address in Decatur County, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Key Growing Facts for Decatur County, Iowa
- USDA Hardiness Zones: 5b (USDA PHZM 2023)
- Last Hard Freeze (28°F): Mar 25 (county normal, NOAA 1991–2020 Climate Normals — light frosts can follow for a few weeks)
- First Hard Freeze (28°F): Nov 12 (county normal, NOAA 1991–2020 Climate Normals — light frosts can arrive a few weeks earlier)
- Days Between Hard Freezes: ~232 (county normal, NOAA 1991–2020 Climate Normals)
- County Land Area: 340K acres (US Census TIGER 2025)
Zone data: USDA ARS Plant Hardiness Zone Map 2023. Climate data: NOAA NCEI. County boundaries: US Census TIGER/Line 2025.
Frost dates here are the Decatur County average. Low spots and tree cover move them by days on any one yard — see your exact frost windows.
Frequently Asked Questions
What hardiness zone is Decatur County, Iowa?
Decatur County sits in USDA hardiness zone 5b, per the USDA Plant Hardiness Zone Map 2023. Zones reflect average annual extreme minimum temperatures from 1991–2020 weather data.
Is it too late to plant in Decatur County?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Feb 25; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 25 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 12 — long-season crops need about 90 days of runway, quick greens only 30. Here the season winds down slowly: late sowings, a real autumn harvest, and garlic in the ground before the first hard freeze.
When does frost risk typically end in Decatur County?
The last hard freeze (28°F) in Decatur County typically lands around Mar 25, per NOAA 1991–2020 climate normals — an earlier marker than the light-frost dates many planting charts quote. That marks the hard freeze, not the last light frost — light frosts can still bite for a few more weeks, so tender transplants usually wait another 2–3 weeks.
How long is the growing season in Decatur County?
Measured between 28°F hard freezes, Decatur County sees about 232 frost-free days — roughly Mar 25 through Nov 12, per NOAA 1991–2020 climate normals. Tender crops get a somewhat shorter practical window, since lighter frosts reach a few weeks past the hard-freeze dates on both ends.
What vegetables grow in Decatur County?
Decatur County's zone 5b supports a wide range — strong performers include Sweet Corn, Tomato, Apple, and Hosta. What actually takes on any one site comes down to its soil, sun, and drainage, and we score each plant against the real conditions at your address.
Which hardiness zone is Decatur County, really?
Officially, Decatur County sits in USDA zone 5b (USDA PHZM 2023) — but a zone is a 30-year average of winter's coldest night across an area, and it can't see any one yard. A south-facing slope, a tree line, or a low frost pocket can shift a single site by half a zone either way, which is why neighboring gardeners often quote different numbers. We read the conditions at your exact address — soil, sun, slope, and frost — and score 1,112 plants against what's actually there.
Is the soil safe to grow vegetables in Decatur County?
The federal record around Decatur County shows 87 documented sites — a typical footprint for a growing area, and proximity to a documented site is information, not a diagnosis of any one yard. It's worth seeing which recorded sites sit closest to where you grow, and testing the soil before new food beds near any of them.
Just moved to Decatur County — what should I know before planting?
Start with three facts. Decatur County sits in USDA zone 5b, which sets what survives winter; the last 28°F hard freeze typically clears around Mar 25, with about 232 frost-free days to work with (NOAA 1991–2020 climate normals); and 87 documented sites sit on the federal record — a typical footprint for a growing area, worth a look on the contamination map before food beds. From there, matching plants to your actual soil and sun is the fun part.
Everything on this page is a Decatur County average. Your yard writes its own version — we read soil, sun, drainage, and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads Iowa's frost window, season length, and soil profile against the plant's real requirements.