St. Clair County, in Missouri, sits in USDA hardiness zone 6b — a zone band wide enough that plant choice, not possibility, is the interesting question.
A short list that earns its place here — tomato, peach, grape, and dogwood — with any one site's soil, sun, and drainage making the final cut.
St. Clair County lies within the Ozarks — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
St. Clair County holds more than one microclimate.
Soils and elevations shift across St. Clair 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
6b
Last Hard Freeze (28°F)
Mar 7
County normal — light frosts run a few weeks later
First Hard Freeze (28°F)
Nov 29
County normal — light frosts arrive a few weeks earlier
County Area
432K acres
Hardiness Zone Range
Zone maps are averages across St. Clair County. Your yard's slope, trees, and frost pockets shift what actually grows — see your land's exact reading.
Soil in St. Clair County
Across St. Clair County, the ground is predominantly Alfisols, where Goss, Barden, and Hector are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 5.6–6.2, moderately acidic. Rainfall drains through hydrologic group C soils.
Soil order
Alfisols
Drainage
Well drained
Prime farmland
20%
Hydric soils
4%
Soil still varies lot by lot — soil types explained.
What Grows in St. Clair County
Plants matched to St. Clair County's USDA zones 6b — each links to its full growing profile.
Is it too late to plant in St. Clair 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 Feb 7; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 7 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 29 — long-season crops need about 90 days of runway, quick greens only 30. With almost year-round growing weather, timing is about heat and rainfall more than frost — some bench is always in play.
Growing Challenges in Missouri
What an experienced grower plans around here — each one has a move.
Highly variable weather with late frosts and early heat
Let your local frost normals call the plantings — Missouri springs punish the calendar-planters and reward the patient.
Heavy clay soils in many regions
Raised beds solve clay drainage the first weekend — and yearly compost turns the ground under them into loam.
Ozark soils are thin and rocky
One soil test shows what thin Ozark ground actually holds — then build up with compost or beds where the depth runs out.
For cultivar selection, pest pressure, and planting-time guidance specific to Missouri, the MU Extension is the authoritative local source.
Safe to Grow Here?
What the federal record shows across St. Clair County — and how to grow with it.
We checked the federal record across St. Clair County — 58 documented sites across 4 of the 9 source types we track.
The most significant on record: 1 mining site. Historic and active mines that may leach heavy metals like arsenic, lead, and cadmium.
The federal record across St. Clair 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 St. Clair County
Severity Distribution
across St. Clair County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around St. Clair County, two things run higher than the national average — Nitrate (16 sites) and Underground Storage Tanks (38 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.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in St. Clair 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
St. Clair County Average
- ●USDA Zones 6b
- ●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 St. Clair County
Pull a site-specific report for your exact address in St. Clair County, Missouri — 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 St. Clair County, Missouri
- USDA Hardiness Zones: 6b (USDA PHZM 2023)
- Last Hard Freeze (28°F): Mar 7 (county normal, NOAA 1991–2020 Climate Normals — light frosts can follow for a few weeks)
- First Hard Freeze (28°F): Nov 29 (county normal, NOAA 1991–2020 Climate Normals — light frosts can arrive a few weeks earlier)
- Days Between Hard Freezes: ~267 (county normal, NOAA 1991–2020 Climate Normals)
- County Land Area: 432K 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 St. Clair 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 St. Clair County, Missouri?
St. Clair County sits in USDA hardiness zone 6b, 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 St. Clair 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 Feb 7; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 7 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 29 — long-season crops need about 90 days of runway, quick greens only 30. With almost year-round growing weather, timing is about heat and rainfall more than frost — some bench is always in play.
When does frost risk typically end in St. Clair County?
The last hard freeze (28°F) in St. Clair County typically lands around Mar 7, 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 St. Clair County?
Measured between 28°F hard freezes, St. Clair County sees about 267 frost-free days — roughly Mar 7 through Nov 29, 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 St. Clair County?
St. Clair County's zone 6b supports a wide range — strong performers include Tomato, Peach, Grape, Dogwood, and Blackberry. 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 St. Clair County, really?
Officially, St. Clair County sits in USDA zone 6b (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 St. Clair County?
The federal record around St. Clair County shows 58 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 St. Clair County — what should I know before planting?
Start with three facts. St. Clair County sits in USDA zone 6b, which sets what survives winter; the last 28°F hard freeze typically clears around Mar 7, with about 267 frost-free days to work with (NOAA 1991–2020 climate normals); and 58 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 St. Clair 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 Missouri's frost window, season length, and soil profile against the plant's real requirements.