Cairo, Illinois, sits in USDA hardiness zone 7a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Reliable performers under these conditions include cabbage, hazelnut, california poppy, and collard greens; what your own ground favors still comes down to its soil, sun, and drainage.
Even in Cairo, 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 Cairo 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 Cairo — soil, climate, flood, and parcel records. How we handle your address.
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Cairo — the short answer
Cairo, Illinois: USDA zone 7a, about 241 days between hard freezes, across 4K acres of city.
- USDA zone
- 7a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 18
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Nov 14
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~241
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 4K 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 7a is Cairo's average, not your lot's — a low corner or a tree line moves it. Against Cairo's 241-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Cairo
Each reading below is measured for Cairo itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredCairo runs about 241 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
MeasuredCairo 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 Cairo is in
Cairo sits in the Mississippi Alluvial Plain — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Cairo's own centroid, and it is not what its county reads: Alexander County is mostly Interior River Valleys and Hills. The wider page above you is answering a different question about different ground.
What Grows in Cairo
Every plant below cleared Cairo's own zone 7a and its 241-day season. Each card opens that plant's Illinois profile. How we score.
Is it too late to plant in Cairo?
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 Feb 18; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 18 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 14 — 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 Cairo
Closest first, within ~10 miles of Cairo. Listing isn't leaking, and distance isn't exposure.
- CAIRO CLEANERSBrownfields · 1500 ft
- Andy's Drive-InUnderground Storage Tanks · 1500 ft
- FFP #852Underground Storage Tanks · 1700 ft
- Southern Medical CenterUnderground Storage Tanks · 1900 ft
- SOUTHERN MEDICAL CENTERSuperfund · 1900 ft
- Daystar Care CenterUnderground Storage Tanks · 2000 ft
- D. Koch Uptown ShellUnderground Storage Tanks · 2200 ft
- Maintenance BldgUnderground Storage Tanks · 2300 ft
- Fill Up MartUnderground Storage Tanks · 2300 ft
- Mayflower Bus CompanyUnderground Storage Tanks · 2300 ft
- Cairo Fire DeptUnderground Storage Tanks · 0.6 mi
- BURKART FOAM INCToxics Release Inventory · 0.6 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Cairo'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 Cairo.
Total Sites
174
within ~10 miles of Cairo
Risk Level
Elevated
Highest-severity
3 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Cairo
Severity Distribution
within ~10 miles of Cairo
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Cairo, two things run higher than the national average within ~10 miles of Cairo — Nitrate (64 sites) and Superfund (3 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Check your specific parcel in Cairo
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 Cairo average
Your land is one point inside Cairo
Everything above resolves to Cairo as a whole — one PHZM band and one 28°F frost record, read across 4K 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 Cairo Average
Cairo Average
- ●USDA Zones 7a, averaged across Cairo
- ●One soil character for all of Cairo
- ●Frost dates read at Cairo's scale: Mar 18 to Nov 14
YOUR Parcel
- ✓Your exact zone, not Cairo's 7a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Cairo
Pull a site-specific report for your exact address in Cairo, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Cairo averages can't show:
We read public map data around Cairo — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Cairo average
How we know this about Cairo
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 Cairo’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 Cairo
When does frost risk typically end in Cairo?
The last hard freeze (28°F) in Cairo typically lands around Mar 18, 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 8.
When is the first frost in Cairo?
The first hard freeze (28°F) in Cairo typically arrives around Nov 14, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 31, so the watching starts about Oct 15 — about 241 days after the spring freeze cleared.
How long is the growing season in Cairo?
Measured between 28°F hard freezes, Cairo sees about 241 frost-free days — roughly Mar 18 through Nov 14, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 8 to Oct 31, about 206 days.
Is the soil safe to grow vegetables in Cairo?
The federal record around Cairo is a meaningful one — 174 documented sites, mostly Underground Storage Tanks entries (79), the nearest Brownfields record about 0.3 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 Cairo?
From about Oct 15 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 Nov 14 (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 Nov 14. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Cairo's scale — its 7a band and its 241-day season. Your yard writes its own version of Cairo'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 Cairo’s own scale
6 of the readings below were taken at Cairo's own scale — its own ~241-day season between 28°F freezes, the 4,472 acres it covers and 174 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Cairo's own USDA hardiness band, zones 7aUSDA PHZM 2023
- Cairo's own 28°F hard-freeze dates, about Mar 18 and Nov 14 and the ~241-day span between themNOAA 1991–2020 Climate Normals
- 174 documented contamination sites on the federal record near Cairo, the closest Brownfields record about 0.3 miles out from the town centreFederal environmental registers
- Cairo's boundary and the 4,472 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 7a and a ~241-day seasonGrowable Ground crop-matching engine
- Cairo sits in the Mississippi Alluvial Plain — not the ecoregion its county mostly readsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Cairo's 4,472 acres read through its county's SSURGO summaryfrom Alexander County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Alexander 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 Alexander County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Cairo's 4,472 acreswhy one lot differs from the next →
- Which side of Cairo you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 4,472 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Brownfields 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 Cairo-wide figureread your own land →