Clark County, in Missouri, sits in USDA hardiness zone 6a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
The conditions favor cabbage, hazelnut, lavender, and collard greens, among others — though every individual site edits that list with its own soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Clark County holds more than one microclimate.
Soils and elevations shift across Clark 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 Clark County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Clark County — the short answer
Clark County, Missouri: USDA zone 6a, about 215 days between hard freezes, across 323K acres.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 2
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Nov 3
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~215
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 323K 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 6a is Clark County's average, not your lot's — a low corner or a tree line moves it. Against Clark County's 215-day season, see what your own ground reads.
Heat in Clark County
Across a year, Clark County accumulates about 3,383 growing degree days above 50°F, about 370 fewer than the middle Missouri county — ahead of 14 of Missouri’s 115 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 Clark County
Across Clark County, the ground is predominantly Alfisols, where Armstrong, Adco, and Lindley are the most extensive named soil series. The soil is generally somewhat poorly drained with a silt loam surface. Topsoil pH runs about 5.7–6.8, slightly acidic. Rainfall drains through hydrologic group D soils.
Soil order
Alfisols
Drainage
Somewhat poorly drained
Prime farmland
2%
Hydric soils
22%
Soil still varies lot by lot — soil types explained.
How the ground varies across Clark County
The USDA soil survey maps 41% of Clark County as somewhat poorly drained — but another 60% drains differently: 22% poorly drained, 19% well drained.
Armstrong is the most extensive named soil at 18% of mapped acres, then Adco (13%) and Lindley (13%).
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 Clark County
Each reading below is measured for Clark 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 Clark County are somewhat poorly drained, in hydrologic group D — ground that sheds water slowly.
Beds can stay saturated for days after heavy rain, and the roots of most vegetables, berries, and fruit trees suffocate or rot in soil that never drains.
Raised beds or mounded rows lift roots above the wet zone; choose water-tolerant crops for the lowest spots.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Clark County runs about pH 5.7–6.8, 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
MeasuredClark County runs about 215 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
MeasuredClark County sits in USDA hardiness zone 6a.
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 Clark County is in
Clark County spans 2 EPA Level III ecoregions — Central Irregular Plains (86%) and Interior River Valleys and Hills (14%). 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 Clark County
We scored all 1,086 plants against Clark County's own USDA zone 6a and its own 215-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 Missouri profile.
Is it too late to plant in Clark 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 5; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 2 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 3 — long-season crops need about 90 days of runway, quick greens only 30. A long window like this one runs successions deep into fall — and even its last weeks take quick greens and garlic.
Documented around Clark County
- monarch butterfly1 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Clark County
USGS estimates 154,044 lb of Atrazine on Clark County farmland in 2019, its largest by weight, ahead of Glyphosate (83,402 lb) and Acetochlor (79,253 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 Clark County — and how to grow with it.
We checked the federal record across Clark County — 92 documented sites across 6 of the 9 source types we track.
The most significant on record: 1 Toxics Release Inventory facility. Active industrial facilities reporting chemical releases to air, water, and land.
The federal record across Clark 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.
What's on the federal record near Clark County
Closest first, across Clark County. Listing isn't leaking, and distance isn't exposure.
- KAHOKA MAINT LOTUnderground Storage Tanks · 0.5 mi
- BILL'S MFA SERVICE STATIONUnderground Storage Tanks · 0.7 mi
- INTEGRATED AGRI INCBrownfields · 0.8 mi
- AYERCO #21Underground Storage Tanks · 0.8 mi
- CASEYS GENERAL STORE #1786Underground Storage Tanks · 0.9 mi
- COLORS UNLIMITEDBrownfields · 0.9 mi
- T65N R08W 36BDC1Nitrate · 1.0 mi
- ROBERT DUER - DUER OIL CO, INCUnderground Storage Tanks · 1.1 mi
- KAHOKA STATIONUnderground Storage Tanks · 1.1 mi
- M & M AMOCO SERVICEUnderground Storage Tanks · 1.1 mi
- BALL FERTILIZERBrownfields · 1.3 mi
- CITY OF KAHOKAUnderground Storage Tanks · 1.3 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Clark 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 Clark County.
Total Sites
92
across Clark County
Risk Level
Moderate
Highest-severity
1 Toxics Release Inventory facility
Sources Checked
across Clark County
Severity Distribution
across Clark County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Clark County, two things run higher than the national average across Clark County — CAFO (4 sites) and Nitrate (50 sites). That's not a problem with your land — it's information about 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 Clark 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 Clark County average
Your land is one point inside Clark County
Everything above resolves to Clark County as a whole — one PHZM band and one county frost record, read across 323K 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 Clark County Average
Clark County Average
- ●USDA Zones 6a, averaged across Clark County
- ●One soil character for all of Clark County
- ●Frost dates read at Clark County's scale: Apr 2 to Nov 3
YOUR Parcel
- ✓Your exact zone, not Clark County's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Clark County
Pull a site-specific report for your exact address in Clark County, Missouri — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Clark County averages can't show:
We read public map data around Clark County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Clark County average
How we know this about Clark 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 Clark County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Clark County
When does frost risk typically end in Clark County?
The last hard freeze (28°F) in Clark County typically lands around Apr 2, 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 23.
How long is the growing season in Clark County?
Measured between 28°F hard freezes, Clark County sees about 215 frost-free days — roughly Apr 2 through Nov 3, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 23 to Oct 20, about 180 days.
Is the soil safe to grow vegetables in Clark County?
The federal record around Clark County shows 92 documented sites, mostly Nitrate entries (50), the nearest Underground Storage Tanks record about 0.5 miles out — 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.
Everything above is measured at Clark County's scale — its 6a band and its 215-day season. Your yard writes its own version of Clark 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 Missouri's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Clark County’s own scale
9 of the readings below were taken at Clark County's own scale — its own ~215-day span between 28°F freezes, the 3 most extensive soil series mapped here and 92 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Clark County's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Clark County's own 28°F hard-freeze dates and its ~215-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Clark CountyUSDA NRCS SSURGO
- 92 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.5 miles outFederal environmental registers
- Clark County's boundary and the 322,948 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~215-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Clark County spans, Central Irregular Plains the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Clark County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Clark County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Missouri grower plans around — written at state scale, so they stay on the state guidefrom Missouri
What this page can’t tell you
- How the season shifts across Clark County — the ~215 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 Clark County's 322,948 acreswhy one lot differs from the next →
- Which of those 92 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 Clark Countyread your own land →