Monmouth, Illinois, sits in USDA hardiness zone 5b — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
The conditions favor cabbage, cranberry, lavender, and collard greens, among others — though every individual site edits that list with its own soil, sun, and drainage.
Even in Monmouth, 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 Monmouth 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 Monmouth — soil, climate, flood, and parcel records. How we handle your address.
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Monmouth — the short answer
Monmouth, Illinois: USDA zone 5b, about 200 days between hard freezes, across 3K acres of city.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 9
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 26
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~200
- 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 Monmouth's average, not your lot's — a low corner or a tree line moves it. Against Monmouth's 200-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Monmouth
Each reading below is measured for Monmouth itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredMonmouth runs about 200 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
MeasuredMonmouth 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 Monmouth is in
Monmouth sits in the Interior River Valleys and Hills — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Monmouth's own centroid rather than borrowed from Warren County.
What Grows in Monmouth
Every plant below cleared Monmouth's own zone 5b and its 200-day season. Each card opens that plant's Illinois profile. How we score.
Is it too late to plant in Monmouth?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Mar 12; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 9 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 26 — long-season crops need about 90 days of runway, quick greens only 30. There is slack in a calendar like this — late plantings, second rounds of favorites, and a fall bench that keeps beds working.
What's on the federal record near Monmouth
Closest first, within ~10 miles of Monmouth. Listing isn't leaking, and distance isn't exposure.
- SMITHFIELD FRESH MEATS CORPToxics Release Inventory · 1400 ft
- Yorkwood FacUnderground Storage Tanks · 1500 ft
- Lenox Township OfUnderground Storage Tanks · 1500 ft
- Lybarger Trading PostUnderground Storage Tanks · 1500 ft
- Quarry Hale Township OfUnderground Storage Tanks · 1500 ft
- Stock Land Fs IncUnderground Storage Tanks · 1500 ft
- Former Vista StoreUnderground Storage Tanks · 1600 ft
- Frieden LonnieUnderground Storage Tanks · 1600 ft
- GTEUnderground Storage Tanks · 1700 ft
- CemetaryUnderground Storage Tanks · 1700 ft
- Family VideoUnderground Storage Tanks · 1800 ft
- Ayerco #26 Convenience CenterUnderground Storage Tanks · 1800 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Monmouth'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 Monmouth.
Total Sites
135
within ~10 miles of Monmouth
Risk Level
Moderate
Highest-severity
6 Toxics Release Inventory facilities
Sources Checked
within ~10 miles of Monmouth
Severity Distribution
within ~10 miles of Monmouth
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Monmouth, CAFO runs higher than the national average — 10 sites within ~10 miles of Monmouth. That's not a problem with your land — it's information about it.
CAFO: CAFOs pose a different contamination profile than chemical sources.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Check your specific parcel in Monmouth
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 Monmouth average
Your land is one point inside Monmouth
Everything above resolves to Monmouth 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 Monmouth Average
Monmouth Average
- ●USDA Zones 5b, averaged across Monmouth
- ●One soil character for all of Monmouth
- ●Frost dates read at Monmouth's scale: Apr 9 to Oct 26
YOUR Parcel
- ✓Your exact zone, not Monmouth's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Monmouth
Pull a site-specific report for your exact address in Monmouth, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Monmouth averages can't show:
We read public map data around Monmouth — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Monmouth average
How we know this about Monmouth
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 Monmouth’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 Monmouth
When does frost risk typically end in Monmouth?
The last hard freeze (28°F) in Monmouth typically lands around Apr 9, 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 30.
When is the first frost in Monmouth?
The first hard freeze (28°F) in Monmouth typically arrives around Oct 26, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 12, so the watching starts about Sep 26 — about 200 days after the spring freeze cleared.
How long is the growing season in Monmouth?
Measured between 28°F hard freezes, Monmouth sees about 200 frost-free days — roughly Apr 9 through Oct 26, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 30 to Oct 12, about 165 days.
Is the soil safe to grow vegetables in Monmouth?
The federal record around Monmouth shows 135 documented sites, mostly Underground Storage Tanks entries (82), the nearest Toxics Release Inventory record about 0.3 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 Monmouth?
From about Sep 26 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 26 (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 26. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Monmouth's scale — its 5b band and its 200-day season. Your yard writes its own version of Monmouth'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 Monmouth’s own scale
6 of the readings below were taken at Monmouth's own scale — its own ~200-day season between 28°F freezes, the 2,716 acres it covers and 135 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Monmouth's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Monmouth's own 28°F hard-freeze dates, about Apr 9 and Oct 26 and the ~200-day span between themNOAA 1991–2020 Climate Normals
- 135 documented contamination sites on the federal record near Monmouth, the closest Toxics Release Inventory record about 0.3 miles out from the town centreFederal environmental registers
- Monmouth's boundary and the 2,716 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~200-day seasonGrowable Ground crop-matching engine
- The ecoregion at Monmouth's own centroid, the Interior River Valleys and HillsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Monmouth's 2,716 acres read through its county's SSURGO summaryfrom Warren County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Warren 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 Warren County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Monmouth's 2,716 acreswhy one lot differs from the next →
- Which side of Monmouth you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 2,716 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Toxics Release Inventory record about 0.3 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 Monmouth-wide figureread your own land →
More in Illinois
Wider growing context
What grows across IllinoisMonmouth sits outside our named growing regions, so Illinois as a whole is its closest context here.
Nearby growing guides