Marion County, in Iowa, sits in USDA hardiness zone 5b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Crops well matched to these conditions include cabbage, cranberry, lavender, and collard greens — though what thrives on any one site still turns on its specific soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Marion County holds more than one microclimate.
Soils and elevations shift across Marion 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 Marion County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Marion County — the short answer
Marion County, Iowa: USDA zone 5b, about 204 days between hard freezes, across 355K acres.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 7
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 28
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~204
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 355K 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 5b is Marion County's average, not your lot's — a low corner or a tree line moves it. Against Marion County's 204-day season, see what your own ground reads.
Heat in Marion County
Across a year, Marion County accumulates about 3,054 growing degree days above 50°F, about 310 more than the middle Iowa county — ahead of 86 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 Marion County
Across Marion County, the ground is predominantly Alfisols, where Munterville, Ladoga, and Clinton are the most extensive named soil series. The soil is generally moderately well drained with a silt loam surface. Topsoil pH runs about 6.0–6.5, slightly acidic. Rainfall drains through hydrologic group C soils.
Soil order
Alfisols
Drainage
Moderately well drained
Prime farmland
19%
Hydric soils
13%
Soil still varies lot by lot — soil types explained.
How the ground varies across Marion County
The USDA soil survey maps 46% of Marion County as moderately well drained — but another 48% drains differently: 17% well drained, 16% poorly drained.
Munterville is the most extensive named soil at 10% of mapped acres, then Ladoga (9%) and Clinton (9%).
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 Marion County
Each reading below is measured for Marion 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 Marion County are moderately well drained, in hydrologic group C — roughly the middle of the drainage range.
This is close to the middle most vegetables prefer: it holds enough water to carry a crop between rains without staying waterlogged. The catch is that a wet spring or a low corner can still tip it soggy.
Plant on the site as-is for most crops, but keep the lowest, slowest-draining beds for moisture-tolerant plantings.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Marion County runs about pH 6.0–6.5, 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
Season length
MeasuredMarion County runs about 204 days between hard freezes — a long growing season.
There is slack for succession plantings and slow-finishing crops: many vegetables can be sown twice, and the heat-lovers have time to ripen fully.
Plan a second sowing of quick crops after the first comes out, and use the fall window most gardeners let sit idle.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredMarion County sits in USDA hardiness zone 5b.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country Marion County is in
Marion County spans 2 EPA Level III ecoregions — Western Corn Belt Plains (70%) and Central Irregular Plains (30%). Which one your land falls in changes what grows wild there and how the ground behaves, and a county-wide answer cannot tell you which.
What Grows in Marion County
We scored all 1,086 plants against Marion County's own USDA zone 5b and its own 204-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 Marion County?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. Cool-season crops can go in from around Mar 10; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 7 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 28 — long-season crops need about 90 days of runway, quick greens only 30. With a season this long, “too late” mostly means “switch crops” — second sowings and a full fall garden are the norm, with garlic closing the year.
What gets applied to farmland in Marion County
USGS estimates 112,645 lb of Glyphosate on Marion County farmland in 2019, its largest by weight, ahead of Metolachlor & Metolachlor-s (61,088 lb) and Atrazine (54,906 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 Marion County — and how to grow with it.
We checked the federal record across Marion County — 367 documented sites across 7 of the 9 source types we track.
The most significant on record: 1 Superfund site (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
There's a meaningful federal record across Marion 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 Marion County
Closest first, across Marion County. Listing isn't leaking, and distance isn't exposure.
- KNOXVILLE STREET SHOPUnderground Storage Tanks · 0.6 mi
- 075N20W01DDAA 19961 1967Knoxville 1Nitrate · 0.6 mi
- 076N19W31DC 20042 1968Knoxville 2Nitrate · 0.7 mi
- VINCE ORR TRUCKING INCUnderground Storage Tanks · 0.7 mi
- MOEN BODY SHOPBrownfields · 0.7 mi
- MCCORMICK FEED & GRAINUnderground Storage Tanks · 0.8 mi
- JULINES FOREIGN CAR RPRBrownfields · 0.8 mi
- CONSUMER OIL COUnderground Storage Tanks · 0.8 mi
- KIRKWOOD RADIATOR SHOPUnderground Storage Tanks · 0.8 mi
- AGAN C FLEMING INCUnderground Storage Tanks · 0.8 mi
- DEVORE CHEVROLET INCUnderground Storage Tanks · 0.8 mi
- DEVORE CHEVROLET INCBrownfields · 0.8 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Marion 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 Marion County.
Total Sites
367
across Marion County
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
across Marion County
Severity Distribution
across Marion County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Marion County, two things run higher than the national average across Marion County — Nitrate (152 sites) and PFAS (4 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Check your specific parcel in Marion 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 Marion County average
Your land is one point inside Marion County
Everything above resolves to Marion County as a whole — one PHZM band and one county frost record, read across 355K 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 Marion County Average
Marion County Average
- ●USDA Zones 5b, averaged across Marion County
- ●One soil character for all of Marion County
- ●Frost dates read at Marion County's scale: Apr 7 to Oct 28
YOUR Parcel
- ✓Your exact zone, not Marion County's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Marion County
Pull a site-specific report for your exact address in Marion County, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Marion County averages can't show:
We read public map data around Marion County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Marion County average
How we know this about Marion 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 Marion County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Marion County
When does frost risk typically end in Marion County?
The last hard freeze (28°F) in Marion County typically lands around Apr 7, 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 Apr 28.
How long is the growing season in Marion County?
Measured between 28°F hard freezes, Marion County sees about 204 frost-free days — roughly Apr 7 through Oct 28, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 28 to Oct 14, about 169 days.
Is the soil safe to grow vegetables in Marion County?
The federal record around Marion County is a meaningful one — 367 documented sites, mostly Nitrate entries (152), the nearest Underground Storage Tanks record about 0.6 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 Marion County's scale — its 5b band and its 204-day season. Your yard writes its own version of Marion 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 Marion County’s own scale
8 of the readings below were taken at Marion County's own scale — its own ~204-day span between 28°F freezes, the 3 most extensive soil series mapped here and 367 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Marion County's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Marion County's own 28°F hard-freeze dates and its ~204-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Marion CountyUSDA NRCS SSURGO
- 367 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.6 miles outFederal environmental registers
- Marion County's boundary and the 354,873 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~204-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Marion County spans, Western Corn Belt Plains the largestUS EPA Level III Ecoregions
- Which agricultural compounds go onto Marion 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 Marion County — the ~204 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 Marion County's 354,873 acreswhy one lot differs from the next →
- Which of those 367 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 Marion Countyread your own land →