Carroll County, in Iowa, sits in USDA hardiness zone 5a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
On paper, cabbage, cranberry, lavender, and collard greens all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Carroll County holds more than one microclimate.
Soils and elevations shift across Carroll County, so your frost dates and drainage aren't the county average. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Carroll County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Carroll County — the short answer
Carroll County, Iowa: USDA zone 5a, about 190 days between hard freezes, across 364K acres.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 14
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 21
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~190
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 364K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 5a is Carroll County's average, not your lot's — a low corner or a tree line moves it. Against Carroll County's 190-day season, see what your own ground reads.
Heat in Carroll County
Across a year, Carroll County accumulates about 2,744 growing degree days above 50°F, right at the Iowa middle — ahead of 49 of Iowa’s 99 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Carroll County
Across Carroll County, the ground is predominantly Mollisols, where Clarion, Colo, and Nicollet are the most extensive named soil series. The soil is generally well drained with a silty clay loam surface. Topsoil pH runs about 6.0–6.4, slightly acidic. Rainfall drains through hydrologic group C soils.
Soil order
Mollisols
Drainage
Well drained
Prime farmland
31%
Hydric soils
28%
Soil still varies lot by lot — soil types explained.
How the ground varies across Carroll County
The USDA soil survey maps 57% of Carroll County as well drained — but another 42% drains differently: 29% poorly drained, 11% somewhat poorly drained.
Clarion is the most extensive named soil at 15% of mapped acres, then Colo (12%) and Nicollet (8%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Carroll County
Each reading below is measured for Carroll County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Carroll County are well drained, in hydrologic group C — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Carroll County runs about pH 6.0–6.4, close to neutral.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Wet ground
MeasuredAbout 28% of Carroll County is mapped as hydric — wetland — soil.
If your lot falls in one of those pockets, a standard in-ground bed will fight waterlogging all season, and roots that need air will struggle.
Check how your own ground drains before you dig; raised beds or moisture-loving plantings turn a wet corner from a problem into a niche.
USDA NRCS SSURGO
Season length
MeasuredCarroll County runs about 190 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
The kind of country Carroll County is in
Carroll County sits in the Western Corn Belt Plains — EPA Level III, inside the wider Great Plains. One consistent ecological setting across the whole county.
What Grows in Carroll County
We scored all 1,086 plants against Carroll County's own USDA zone 5a and its own 190-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's Iowa profile.
Is it too late to plant in Carroll County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Mar 17; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 14 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 21 — long-season crops need about 90 days of runway, quick greens only 30. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
Documented around Carroll County
- monarch butterfly2,202 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Carroll County
USGS estimates 338,744 lb of Glyphosate on Carroll County farmland in 2019, its largest by weight, ahead of Acetochlor (138,922 lb) and Metolachlor & Metolachlor-s (108,284 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Carroll County — and how to grow with it.
We checked the federal record across Carroll County — 357 documented sites across 6 of the 9 source types we track.
The most significant on record: 13 Toxics Release Inventory facilities. Active industrial facilities reporting chemical releases to air, water, and land.
There's a meaningful federal record across Carroll County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Carroll County
Closest first, across Carroll County. Listing isn't leaking, and distance isn't exposure.
- CAL CAR SERVICE COUnderground Storage Tanks · 2200 ft
- 084N35W25DCAB 1968Carroll 12Nitrate · 0.9 mi
- GENERAL EXCAVATING INCUnderground Storage Tanks · 0.9 mi
- NORTHERN NATURAL GAS - CARROLL TBSBrownfields · 1.0 mi
- 084N35W25DBCB 37480 1957Carroll 11Nitrate · 1.0 mi
- 084N35W25CAAA 06526 1953Carroll 10Nitrate · 1.2 mi
- ST. ANTHONY HOSPITALBrownfields · 1.2 mi
- 084N35W25BDDC 01398 1939Carroll 6Nitrate · 1.2 mi
- 084N35W25BDD 02958 1947Carroll 7Nitrate · 1.3 mi
- 084N35W25BDAD 00190 1939Carroll Test 1Nitrate · 1.3 mi
- 083N35W11AAAA 00417 1936Nitrate · 1.3 mi
- 084N35W25BDBC 1974Carroll 13Nitrate · 1.4 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Carroll County's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near Carroll County.
Total Sites
357
across Carroll County
Risk Level
Elevated
Highest-severity
13 Toxics Release Inventory facilities
Sources Checked
across Carroll County
Severity Distribution
across Carroll County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Carroll County, two things run higher than the national average across Carroll County — CAFO (11 sites) and Nitrate (174 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
CAFO: CAFOs pose a different contamination profile than chemical sources.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Carroll County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the Carroll County average
Your land is one point inside Carroll County
Everything above resolves to Carroll County as a whole — one PHZM band and one county frost record, read across 364K acres. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at county scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better county average.
Your Lot vs the Carroll County Average
Carroll County Average
- ●USDA Zones 5a, averaged across Carroll County
- ●One soil character for all of Carroll County
- ●Frost dates read at Carroll County's scale: Apr 14 to Oct 21
YOUR Parcel
- ✓Your exact zone, not Carroll County's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Carroll County
Pull a site-specific report for your exact address in Carroll County, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Carroll County averages can't show:
We read public map data around Carroll County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Carroll County average
How we know this about Carroll County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Carroll County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Carroll County
When does frost risk typically end in Carroll County?
The last hard freeze (28°F) in Carroll County typically lands around Apr 14, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about May 5.
How long is the growing season in Carroll County?
Measured between 28°F hard freezes, Carroll County sees about 190 frost-free days — roughly Apr 14 through Oct 21, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 5 to Oct 7, about 155 days.
Is the soil safe to grow vegetables in Carroll County?
The federal record around Carroll County is a meaningful one — 357 documented sites, mostly Nitrate entries (174), the nearest Underground Storage Tanks record about 0.4 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
Everything above is measured at Carroll County's scale — its 5a band and its 190-day season. Your yard writes its own version of Carroll County's numbers: 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.
What this page reads at Carroll County’s own scale
9 of the readings below were taken at Carroll County's own scale — its own ~190-day span between 28°F freezes, the 3 most extensive soil series mapped here and 357 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Carroll County's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Carroll County's own 28°F hard-freeze dates and its ~190-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Carroll CountyUSDA NRCS SSURGO
- 357 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.4 miles outFederal environmental registers
- Carroll County's boundary and the 364,450 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~190-day seasonGrowable Ground crop-matching engine
- Carroll County sitting wholly inside the Western Corn Belt PlainsUS EPA Level III Ecoregions
- Open occurrence records documented in Carroll County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Carroll County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Iowa grower plans around — written at state scale, so they stay on the state guidefrom Iowa
What this page can’t tell you
- How the season shifts across Carroll County — the ~190 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Carroll County's 364,450 acreswhy one lot differs from the next →
- Which of those 357 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Carroll Countyread your own land →