Rock Falls, Illinois, sits in USDA hardiness zone 5b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Growers here do well with cabbage, cranberry, lavender, and collard greens — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Even in Rock Falls, 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 Falls 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 Falls — soil, climate, flood, and parcel records. How we handle your address.
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Rock Falls — the short answer
Rock Falls, Illinois: USDA zone 5b, about 192 days between hard freezes, across 3K acres of city.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 11
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 20
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~192
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 3K 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 5b is Rock Falls's average, not your lot's — a low corner or a tree line moves it. Against Rock Falls's 192-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Rock Falls
Each reading below is measured for Rock Falls itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredRock Falls runs about 192 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 Falls sits in USDA hardiness zone 5b.
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 Falls is in
Rock Falls sits in the Central Corn Belt Plains — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Rock Falls's own centroid rather than borrowed from Whiteside County.
What Grows in Rock Falls
Every plant below cleared Rock Falls's own zone 5b and its 192-day season. Each card opens that plant's Illinois profile. How we score.
Is it too late to plant in Rock Falls?
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 14; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 11 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 20 — long-season crops need about 90 days of runway, quick greens only 30. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
What's on the federal record near Rock Falls
Closest first, within ~10 miles of Rock Falls. Listing isn't leaking, and distance isn't exposure.
- Civic Plaza IUnderground Storage Tanks · 600 ft
- FMS 11 Rock FallsUnderground Storage Tanks · 850 ft
- Rock Falls Fire DeptUnderground Storage Tanks · 950 ft
- MILITARY & NAVAL DEPT - ROCK FALLS NGBrownfields · 1000 ft
- CheckersUnderground Storage Tanks · 1400 ft
- OREILLY AUTO PARTS 1171Brownfields · 1400 ft
- DOLLAR GENERAL STORE 3141Brownfields · 1400 ft
- T D Kurtz Glass Co IncUnderground Storage Tanks · 1400 ft
- ROBS ALIGNMENTBrownfields · 1500 ft
- Casey's General StoreUnderground Storage Tanks · 1500 ft
- Thomeway LinesUnderground Storage Tanks · 1600 ft
- Shore Acres MarinaUnderground Storage Tanks · 1600 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Rock Falls'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 Falls.
Total Sites
262
within ~10 miles of Rock Falls
Risk Level
Elevated
Highest-severity
5 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Rock Falls
Severity Distribution
within ~10 miles of Rock Falls
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Rock Falls, two things run higher than the national average within ~10 miles of Rock Falls — Superfund (5 sites) and Toxics Release Inventory (24 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Toxics Release Inventory: TRI facilities report annual chemical releases to air, water, and land.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Check prevailing wind direction — downwind parcels face higher exposure than upwind or crosswind locations.
Check your specific parcel in Rock Falls
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 Falls average
Your land is one point inside Rock Falls
Everything above resolves to Rock Falls as a whole — one PHZM band and one 28°F frost record, read across 3K 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 city 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 Falls Average
Rock Falls Average
- ●USDA Zones 5b, averaged across Rock Falls
- ●One soil character for all of Rock Falls
- ●Frost dates read at Rock Falls's scale: Apr 11 to Oct 20
YOUR Parcel
- ✓Your exact zone, not Rock Falls's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Rock Falls
Pull a site-specific report for your exact address in Rock Falls, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Rock Falls averages can't show:
We read public map data around Rock Falls — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Rock Falls average
How we know this about Rock Falls
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Rock Falls’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 city grain anywhere on this page — there is no city-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 Falls
When does frost risk typically end in Rock Falls?
The last hard freeze (28°F) in Rock Falls typically lands around Apr 11, 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 2.
When is the first frost in Rock Falls?
The first hard freeze (28°F) in Rock Falls typically arrives around Oct 20, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 6, so the watching starts about Sep 20 — about 192 days after the spring freeze cleared.
How long is the growing season in Rock Falls?
Measured between 28°F hard freezes, Rock Falls sees about 192 frost-free days — roughly Apr 11 through Oct 20, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 2 to Oct 6, about 157 days.
Is the soil safe to grow vegetables in Rock Falls?
The federal record around Rock Falls is a meaningful one — 262 documented sites, mostly Underground Storage Tanks entries (152), the nearest Underground Storage Tanks record about 0.1 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.
How do I protect my plants from frost in Rock Falls?
From about Sep 20 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 20 (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 20. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Rock Falls's scale — its 5b band and its 192-day season. Your yard writes its own version of Rock Falls'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 Falls’s own scale
6 of the readings below were taken at Rock Falls's own scale — its own ~192-day season between 28°F freezes, the 2,549 acres it covers and 262 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Rock Falls's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Rock Falls's own 28°F hard-freeze dates, about Apr 11 and Oct 20 and the ~192-day span between themNOAA 1991–2020 Climate Normals
- 262 documented contamination sites on the federal record near Rock Falls, the closest Underground Storage Tanks record about 0.1 miles out from the town centreFederal environmental registers
- Rock Falls's boundary and the 2,549 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~192-day seasonGrowable Ground crop-matching engine
- The ecoregion at Rock Falls's own centroid, the Central Corn Belt PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Rock Falls's 2,549 acres read through its county's SSURGO summaryfrom Whiteside County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Whiteside 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 Whiteside County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Rock Falls's 2,549 acreswhy one lot differs from the next →
- Which side of Rock Falls you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 2,549 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 Falls-wide figureread your own land →
More in Illinois
Wider growing context
What grows across IllinoisRock Falls sits outside our named growing regions, so Illinois as a whole is its closest context here.