Randolph County, in Illinois, sits in USDA hardiness zone 7a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
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
Randolph County holds more than one microclimate.
Soils and elevations shift across Randolph 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 Randolph County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Randolph County — the short answer
Randolph County, Illinois: USDA zone 7a, about 224 days between hard freezes, across 368K acres.
- USDA zone
- 7a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 26
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Nov 5
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~224
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 368K 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 Randolph County's average, not your lot's — a low corner or a tree line moves it. Against Randolph County's 224-day season, see what your own ground reads.
Heat in Randolph County
Across a year, Randolph County accumulates about 3,967 growing degree days above 50°F, about 584 more than the middle Illinois county — ahead of 90 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 Randolph County
Across Randolph County, the ground is predominantly Alfisols, where Menfro, Bunkum, 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 6.2–6.5, slightly acidic. Rainfall drains through hydrologic group C/D soils.
Soil order
Alfisols
Drainage
Somewhat poorly drained
Prime farmland
22%
Hydric soils
10%
Soil still varies lot by lot — soil types explained.
How the ground varies across Randolph County
The USDA soil survey maps 39% of Randolph County as somewhat poorly drained — but another 59% drains differently: 31% well drained, 18% moderately well drained.
Menfro is the most extensive named soil at 15% of mapped acres, then Bunkum (11%) and Marine (10%).
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 Randolph County
Each reading below is measured for Randolph 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 Randolph 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 Randolph County runs about pH 6.2–6.5, 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
MeasuredRandolph County runs about 224 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
MeasuredRandolph 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 Randolph County is in
Randolph 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 Randolph County
We scored all 1,086 plants against Randolph County's own USDA zone 7a and its own 224-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 Randolph County?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Feb 26; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 26 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 5 — 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 Randolph County
- Japanese beetle1 documented records
- monarch butterfly15 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Randolph County
USGS estimates 171,648 lb of Glyphosate on Randolph County farmland in 2019, its largest by weight, ahead of Metolachlor & Metolachlor-s (168,408 lb) and Metolachlor-s (132,410 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 Randolph County — and how to grow with it.
We checked the federal record across Randolph County — 211 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 Randolph 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 Randolph County
Closest first, across Randolph County. Listing isn't leaking, and distance isn't exposure.
- Walsh RadioUnderground Storage Tanks · 2.8 mi
- Crop Production ServicesUnderground Storage Tanks · 2.8 mi
- CHESTERPFAS · 5.0 mi
- Ellis Grove Service StationUnderground Storage Tanks · 5.5 mi
- 1 mile NE of EvansvilleNitrate · 5.8 mi
- Niederbrach Truck Ser IncUnderground Storage Tanks · 6.2 mi
- Thomas DunkerUnderground Storage Tanks · 6.3 mi
- Evansville Cement Finishers IncUnderground Storage Tanks · 6.4 mi
- Kaskaskia Regional Port DistrictUnderground Storage Tanks · 6.4 mi
- ROESCH, INC.Toxics Release Inventory · 6.6 mi
- Village Of EvansvilleUnderground Storage Tanks · 6.8 mi
- Kisro Conoco Bulk PlantUnderground Storage Tanks · 6.8 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Randolph 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 Randolph County.
Total Sites
211
across Randolph County
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
across Randolph County
Severity Distribution
across Randolph County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Randolph County, two things run higher than the national average across Randolph County — PFAS (3 sites) and Underground Storage Tanks (143 sites). That's not a problem with your land — it's information about it.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Randolph 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 Randolph County average
Your land is one point inside Randolph County
Everything above resolves to Randolph County as a whole — one PHZM band and one county frost record, read across 368K 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 Randolph County Average
Randolph County Average
- ●USDA Zones 7a, averaged across Randolph County
- ●One soil character for all of Randolph County
- ●Frost dates read at Randolph County's scale: Mar 26 to Nov 5
YOUR Parcel
- ✓Your exact zone, not Randolph County's 7a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Randolph County
Pull a site-specific report for your exact address in Randolph County, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Randolph County averages can't show:
We read public map data around Randolph County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Randolph County average
How we know this about Randolph 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 Randolph County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Randolph County
When does frost risk typically end in Randolph County?
The last hard freeze (28°F) in Randolph County typically lands around Mar 26, 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 16.
How long is the growing season in Randolph County?
Measured between 28°F hard freezes, Randolph County sees about 224 frost-free days — roughly Mar 26 through Nov 5, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 16 to Oct 22, about 189 days.
Is the soil safe to grow vegetables in Randolph County?
The federal record around Randolph County is a meaningful one — 211 documented sites, mostly Underground Storage Tanks entries (143), the nearest Underground Storage Tanks record about 2.8 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 Randolph County's scale — its 7a band and its 224-day season. Your yard writes its own version of Randolph 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 Randolph County’s own scale
9 of the readings below were taken at Randolph County's own scale — its own ~224-day span between 28°F freezes, the 3 most extensive soil series mapped here and 211 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Randolph County's own USDA hardiness band, zones 7aUSDA PHZM 2023
- Randolph County's own 28°F hard-freeze dates and its ~224-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Randolph CountyUSDA NRCS SSURGO
- 211 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 2.8 miles outFederal environmental registers
- Randolph County's boundary and the 368,235 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 7a and a ~224-day seasonGrowable Ground crop-matching engine
- Randolph County sitting wholly inside the Interior River Valleys and HillsUS EPA Level III Ecoregions
- Open occurrence records documented in Randolph County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Randolph 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 Randolph County — the ~224 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 Randolph County's 368,235 acreswhy one lot differs from the next →
- Which of those 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 Randolph Countyread your own land →