St. Clair County, in Illinois, sits in USDA hardiness zone 7a — a zone band wide enough that plant choice, not possibility, is the interesting question.
A short list that earns its place here — cabbage, hazelnut, california poppy, and collard greens — 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
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 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around St. Clair County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
St. Clair County — the short answer
St. Clair County, Illinois: USDA zone 7a, about 233 days between hard freezes, across 421K acres.
- USDA zone
- 7a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 24
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Nov 12
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~233
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 421K 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 7a is St. Clair County's average, not your lot's — a low corner or a tree line moves it. Against St. Clair County's 233-day season, see what your own ground reads.
Heat in St. Clair County
Across a year, St. Clair County accumulates about 4,091 growing degree days above 50°F, about 708 more than the middle Illinois county — ahead of 98 of Illinois’s 102 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 St. Clair County
Across St. Clair County, the ground is predominantly Alfisols, where Menfro, Wakeland, and Marine are the most extensive named soil series. The soil is generally somewhat poorly drained with a silt loam surface. Topsoil pH runs about 6.2–6.6, slightly acidic. Rainfall drains through hydrologic group C/D soils.
Soil order
Alfisols
Drainage
Somewhat poorly drained
Prime farmland
23%
Hydric soils
18%
Soil still varies lot by lot — soil types explained.
How the ground varies across St. Clair County
The USDA soil survey maps 44% of St. Clair County as somewhat poorly drained — but another 51% drains differently: 21% well drained, 16% poorly drained.
Menfro is the most extensive named soil at 12% of mapped acres, then Wakeland (8%) and Marine (6%).
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 St. Clair County
Each reading below is measured for St. Clair 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 St. Clair County are somewhat poorly drained, in hydrologic group C/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 St. Clair County runs about pH 6.2–6.6, 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
MeasuredSt. Clair County runs about 233 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
MeasuredSt. Clair County sits in USDA hardiness zone 7a.
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 St. Clair County is in
St. Clair County sits in the Interior River Valleys and Hills — EPA Level III, inside the wider Eastern Temperate Forests. One consistent ecological setting across the whole county.
What Grows in St. Clair County
We scored all 1,086 plants against St. Clair County's own USDA zone 7a and its own 233-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 Illinois 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 24; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 24 (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.
Documented around St. Clair County
Survey cells within 31 miles of St. Clair County checked for spotted lanternfly, none carrying a detection — a surveyed negative, not an absence of looking. Nearest documented record 240 miles off. What to watch for.
- Japanese beetle1 documented records
- monarch butterfly7 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in St. Clair County
USGS estimates 236,602 lb of Metolachlor & Metolachlor-s on St. Clair County farmland in 2019, its largest by weight, ahead of Glyphosate (223,549 lb) and Metolachlor-s (190,163 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 St. Clair County — and how to grow with it.
We checked the federal record across St. Clair County — 1,211 documented sites across 8 of the 9 source types we track.
The most significant on record: 38 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
St. Clair County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near St. Clair County
Closest first, across St. Clair County. Listing isn't leaking, and distance isn't exposure.
- PEABODY COAL CO RIVER KING NO 1 MINEBrownfields · 1.5 mi
- KETTLER CASTING CO INCToxics Release Inventory · 1.6 mi
- 1 mile N of FreeburgNitrate · 1.8 mi
- 2 miles NW of FreeburgNitrate · 1.8 mi
- PARCO MAINTENANCE, INC.Brownfields · 1.9 mi
- IDOT BELLEVILLE 811Brownfields · 1.9 mi
- St Clair Service CompanyUnderground Storage Tanks · 2.0 mi
- DOLLAR GENERAL STORE 7256Brownfields · 2.0 mi
- Commercial Transport, Inc.Underground Storage Tanks · 2.1 mi
- BELLEVILLE SHOE MFG COToxics Release Inventory · 2.2 mi
- Belleville Shoe Manufacturing CoUnderground Storage Tanks · 2.2 mi
- Ruts Moving & Delivery ServUnderground Storage Tanks · 2.3 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from St. Clair 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 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, Superfund runs higher than the national average — 38 sites across St. Clair County. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Check your specific parcel in St. Clair County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the St. Clair County average
Your land is one point inside St. Clair County
Everything above resolves to St. Clair County as a whole — one PHZM band and one county frost record, read across 421K 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 St. Clair County Average
St. Clair County Average
- ●USDA Zones 7a, averaged across St. Clair County
- ●One soil character for all of St. Clair County
- ●Frost dates read at St. Clair County's scale: Mar 24 to Nov 12
YOUR Parcel
- ✓Your exact zone, not St. Clair County's 7a
- ✓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, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that St. Clair County averages can't show:
We read public map data around St. Clair County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the St. Clair County average
How we know this about St. Clair 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 St. Clair County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about St. Clair County
When does frost risk typically end in St. Clair County?
The last hard freeze (28°F) in St. Clair County typically lands around Mar 24, 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 14.
How long is the growing season in St. Clair County?
Measured between 28°F hard freezes, St. Clair County sees about 233 frost-free days — roughly Mar 24 through Nov 12, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 14 to Oct 29, about 198 days.
Is the soil safe to grow vegetables in St. Clair County?
The federal record around St. Clair County runs heavier than most — 1,211 documented sites, mostly Underground Storage Tanks entries (689), the nearest Brownfields record about 1.5 miles out — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.
Everything above is measured at St. Clair County's scale — its 7a band and its 233-day season. Your yard writes its own version of St. Clair 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 Illinois's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at St. Clair County’s own scale
9 of the readings below were taken at St. Clair County's own scale — its own ~233-day span between 28°F freezes, the 3 most extensive soil series mapped here and 1,211 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- St. Clair County's own USDA hardiness band, zones 7aUSDA PHZM 2023
- St. Clair County's own 28°F hard-freeze dates and its ~233-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in St. Clair CountyUSDA NRCS SSURGO
- 1,211 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Brownfields record about 1.5 miles outFederal environmental registers
- St. Clair County's boundary and the 420,959 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 7a and a ~233-day seasonGrowable Ground crop-matching engine
- St. Clair County sitting wholly inside the Interior River Valleys and HillsUS EPA Level III Ecoregions
- Open occurrence records documented in St. Clair County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto St. Clair County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Illinois grower plans around — written at state scale, so they stay on the state guidefrom Illinois
What this page can’t tell you
- How the season shifts across St. Clair County — the ~233 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 St. Clair County's 420,959 acreswhy one lot differs from the next →
- Which of those 1,211 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 St. Clair Countyread your own land →