Thomson, Illinois, sits in USDA hardiness zone 5b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Crops well matched to these conditions include cabbage, cranberry, lavender, and collard greens — though what thrives on any one site still turns on its specific soil, sun, and drainage.
Even in Thomson, 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 Thomson 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 Thomson — soil, climate, flood, and parcel records. How we handle your address.
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Thomson — the short answer
Thomson, Illinois: USDA zone 5b, about 204 days between hard freezes, across 1K acres of town.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 7
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 28
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~204
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 1K 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 Thomson's average, not your lot's — a low corner or a tree line moves it. Against Thomson's 204-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Thomson
Each reading below is measured for Thomson itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredThomson runs about 204 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
MeasuredThomson 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 Thomson is in
Thomson sits in the Interior River Valleys and Hills — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Thomson's own centroid, and it is not what its county reads: Carroll County is mostly Central Corn Belt Plains. The wider page above you is answering a different question about different ground.
What Grows in Thomson
Every plant below cleared Thomson's own zone 5b and its 204-day season. Each card opens that plant's Illinois profile. How we score.
Is it too late to plant in Thomson?
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 10; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 7 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 28 — 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.
What's on the federal record near Thomson
Closest first, within ~10 miles of Thomson. Listing isn't leaking, and distance isn't exposure.
- FEDERAL CORRECTIONAL INSTITUTIONBrownfields · 1100 ft
- USP THOMSONToxics Release Inventory · 1800 ft
- ITC MIDWEST YORK SSBrownfields · 1.0 mi
- Thomson Village OfUnderground Storage Tanks · 1.2 mi
- Casey's General Store #2666Underground Storage Tanks · 1.3 mi
- Casey's General Store #1263Underground Storage Tanks · 1.3 mi
- Burlington NorthernUnderground Storage Tanks · 1.4 mi
- Mcworthy SylvesterUnderground Storage Tanks · 1.4 mi
- Bruckner Lloyd Old School BuildingUnderground Storage Tanks · 1.4 mi
- Atherton Ser IncUnderground Storage Tanks · 1.4 mi
- The StationUnderground Storage Tanks · 1.6 mi
- DANISCO USA, INC.Toxics Release Inventory · 1.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Thomson'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 Thomson.
Total Sites
180
within ~10 miles of Thomson
Risk Level
Elevated
Highest-severity
2 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Thomson
Severity Distribution
within ~10 miles of Thomson
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Thomson, CAFO runs higher than the national average — 6 sites within ~10 miles of Thomson. 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 Thomson
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 Thomson average
Your land is one point inside Thomson
Everything above resolves to Thomson as a whole — one PHZM band and one 28°F frost record, read across 1K 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 Thomson Average
Thomson Average
- ●USDA Zones 5b, averaged across Thomson
- ●One soil character for all of Thomson
- ●Frost dates read at Thomson's scale: Apr 7 to Oct 28
YOUR Parcel
- ✓Your exact zone, not Thomson's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Thomson
Pull a site-specific report for your exact address in Thomson, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Thomson averages can't show:
We read public map data around Thomson — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Thomson average
How we know this about Thomson
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 Thomson’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 Thomson
When does frost risk typically end in Thomson?
The last hard freeze (28°F) in Thomson typically lands around Apr 7, 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 28.
When is the first frost in Thomson?
The first hard freeze (28°F) in Thomson typically arrives around Oct 28, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 14, so the watching starts about Sep 28 — about 204 days after the spring freeze cleared.
How long is the growing season in Thomson?
Measured between 28°F hard freezes, Thomson sees about 204 frost-free days — roughly Apr 7 through Oct 28, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 28 to Oct 14, about 169 days.
Is the soil safe to grow vegetables in Thomson?
The federal record around Thomson is a meaningful one — 180 documented sites, mostly Underground Storage Tanks entries (107), the nearest Brownfields record about 0.2 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 Thomson?
From about Sep 28 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 28 (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 28. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Thomson's scale — its 5b band and its 204-day season. Your yard writes its own version of Thomson'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 Thomson’s own scale
6 of the readings below were taken at Thomson's own scale — its own ~204-day season between 28°F freezes, the 1,420 acres it covers and 180 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Thomson's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Thomson's own 28°F hard-freeze dates, about Apr 7 and Oct 28 and the ~204-day span between themNOAA 1991–2020 Climate Normals
- 180 documented contamination sites on the federal record near Thomson, the closest Brownfields record about 0.2 miles out from the town centreFederal environmental registers
- Thomson's boundary and the 1,420 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~204-day seasonGrowable Ground crop-matching engine
- Thomson sits in the Interior River Valleys and Hills — not the ecoregion its county mostly readsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Thomson's 1,420 acres read through its county's SSURGO summaryfrom Carroll County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Carroll 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 Carroll County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Thomson's 1,420 acreswhy one lot differs from the next →
- Which side of Thomson you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 1,420 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Brownfields record about 0.2 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 Thomson-wide figureread your own land →
More in Illinois
Wider growing context
What grows across IllinoisThomson sits outside our named growing regions, so Illinois as a whole is its closest context here.
Nearby growing guides