Rock City, Illinois, sits in USDA hardiness zone 5a — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Well-matched crops include cabbage, cranberry, lavender, and collard greens, and the gap between "grows in the area" and "grows in your yard" is closed by soil, sun, and drainage.
Even in Rock City, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Rock City lot. 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 Rock City — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Rock City — the short answer
Rock City, Illinois: USDA zone 5a, about 189 days between hard freezes, across 87 acres of town.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 15
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 21
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~189
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 87 acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are this town’s own 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 5a is Rock City's average, not your lot's — a low corner or a tree line moves it. Against Rock City's 189-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Rock City
Each reading below is measured for Rock City itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredRock City runs about 189 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredRock City sits in USDA hardiness zone 5a.
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 Rock City is in
Rock City sits in the Southeastern Wisconsin Till Plains — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Rock City's own centroid, and it is not what its county reads: Stephenson County is mostly Central Corn Belt Plains. The wider page above you is answering a different question about different ground.
What Grows in Rock City
Every plant below cleared Rock City's own zone 5a and its 189-day season. Each card opens that plant's Illinois profile. How we score.
Is it too late to plant in Rock City?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Mar 18; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 15 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 21 — long-season crops need about 90 days of runway, quick greens only 30. Even past midsummer there is room for a true fall garden here, and garlic planted near the close carries the momentum into next year.
What's on the federal record near Rock City
Closest first, within ~10 miles of Rock City. Listing isn't leaking, and distance isn't exposure.
- Rock City GarageUnderground Storage Tanks · 600 ft
- Fuel Tracker CompanyUnderground Storage Tanks · 650 ft
- Duncan Sales & ServicesUnderground Storage Tanks · 850 ft
- DEVANSOY INCBrownfields · 2.4 mi
- BERNER CHEESE CORPToxics Release Inventory · 2.4 mi
- ILLINI PROTEINToxics Release Inventory · 2.5 mi
- T R MACHINE INCBrownfields · 2.9 mi
- Johnson Oil CompanyUnderground Storage Tanks · 3.0 mi
- Casey's General Store #2434Underground Storage Tanks · 3.0 mi
- Wishard RonaldUnderground Storage Tanks · 3.0 mi
- Dakota GarageUnderground Storage Tanks · 3.1 mi
- Trading PostUnderground Storage Tanks · 3.3 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Rock City'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 Rock City.
Total Sites
91
within ~10 miles of Rock City
Risk Level
Moderate
Highest-severity
6 Toxics Release Inventory facilities
Sources Checked
within ~10 miles of Rock City
Severity Distribution
within ~10 miles of Rock City
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Rock City, two things run higher than the national average within ~10 miles of Rock City — CAFO (6 sites) and Toxics Release Inventory (6 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
CAFO: CAFOs pose a different contamination profile than chemical sources.
Toxics Release Inventory: TRI facilities report annual chemical releases to air, water, and land.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Check prevailing wind direction — downwind parcels face higher exposure than upwind or crosswind locations.
Check your specific parcel in Rock City
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 Rock City average
Your land is one point inside Rock City
Everything above resolves to Rock City as a whole — one PHZM band and one 28°F frost record, read across 87 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 town 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 local average.
Your Lot vs the Rock City Average
Rock City Average
- ●USDA Zones 5a, averaged across Rock City
- ●One soil character for all of Rock City
- ●Frost dates read at Rock City's scale: Apr 15 to Oct 21
YOUR Parcel
- ✓Your exact zone, not Rock City's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Rock City
Pull a site-specific report for your exact address in Rock City, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Rock City averages can't show:
We read public map data around Rock City — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Rock City average
How we know this about Rock City
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this town’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Rock City’s own record; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at town grain anywhere on this page — there is no town-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Rock City
When does frost risk typically end in Rock City?
The last hard freeze (28°F) in Rock City typically lands around Apr 15, 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 May 6.
When is the first frost in Rock City?
The first hard freeze (28°F) in Rock City typically arrives around Oct 21, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 7, so the watching starts about Sep 21 — about 189 days after the spring freeze cleared.
How long is the growing season in Rock City?
Measured between 28°F hard freezes, Rock City sees about 189 frost-free days — roughly Apr 15 through Oct 21, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 6 to Oct 7, about 154 days.
Is the soil safe to grow vegetables in Rock City?
The federal record around Rock City shows 91 documented sites, mostly Underground Storage Tanks entries (51), the nearest Underground Storage Tanks record about 0.1 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.
How do I protect my plants from frost in Rock City?
From about Sep 21 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Oct 21 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Oct 21. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Rock City's scale — its 5a band and its 189-day season. Your yard writes its own version of Rock City's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Rock City’s own scale
6 of the readings below were taken at Rock City's own scale — its own ~189-day season between 28°F freezes, the 87 acres it covers and 91 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Rock City's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Rock City's own 28°F hard-freeze dates, about Apr 15 and Oct 21 and the ~189-day span between themNOAA 1991–2020 Climate Normals
- 91 documented contamination sites on the federal record near Rock City, the closest Underground Storage Tanks record about 0.1 miles out from the town centreFederal environmental registers
- Rock City's boundary and the 87 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~189-day seasonGrowable Ground crop-matching engine
- Rock City sits in the Southeastern Wisconsin Till Plains — not the ecoregion its county mostly readsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Rock City's 87 acres read through its county's SSURGO summaryfrom Stephenson County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Stephenson County
- The growing challenges every Illinois grower plans around — written at state scale, so they stay on the state guidefrom Illinois
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Stephenson County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Rock City's 87 acreswhy one lot differs from the next →
- Which side of Rock City you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 87 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.1 miles out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Rock City-wide figureread your own land →
More in Illinois
Wider growing context
What grows across IllinoisRock City sits outside our named growing regions, so Illinois as a whole is its closest context here.
Nearby growing guides