Winthrop Harbor, Illinois, sits in USDA hardiness zone 6a — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
Growers here do well with cabbage, hazelnut, lavender, and collard greens — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Even in Winthrop Harbor, 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 Winthrop Harbor 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 Winthrop Harbor — soil, climate, flood, and parcel records. How we handle your address.
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Winthrop Harbor — the short answer
Winthrop Harbor, Illinois: USDA zone 6a, about 212 days between hard freezes, across 3K acres of town.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 8
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Nov 6
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~212
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town 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 6a is Winthrop Harbor's average, not your lot's — a low corner or a tree line moves it. Against Winthrop Harbor's 212-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Winthrop Harbor
Each reading below is measured for Winthrop Harbor itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredWinthrop Harbor runs about 212 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
MeasuredWinthrop Harbor sits in USDA hardiness zone 6a.
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 Winthrop Harbor is in
Winthrop Harbor sits in the Central Corn Belt Plains — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Winthrop Harbor's own centroid, and it is not what its county reads: Lake County is mostly Southeastern Wisconsin Till Plains. The wider page above you is answering a different question about different ground.
What Grows in Winthrop Harbor
Every plant below cleared Winthrop Harbor's own zone 6a and its 212-day season. Each card opens that plant's Illinois profile. How we score.
Is it too late to plant in Winthrop Harbor?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 11; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 8 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 6 — 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.
Documented around Winthrop Harbor
Spotted lanternfly documented 22 miles from Winthrop Harbor, first recorded 2023. What to watch for.
What's on the federal record near Winthrop Harbor
Closest first, within ~10 miles of Winthrop Harbor. Listing isn't leaking, and distance isn't exposure.
- WINTHROP HARBORPFAS · 600 ft
- 46N12E-9.1f1Nitrate · 900 ft
- Fire Station Village Of WinthropUnderground Storage Tanks · 1100 ft
- IL-0085Underground Storage Tanks · 1100 ft
- Winthrop MarathonUnderground Storage Tanks · 1100 ft
- MARATHONBrownfields · 1200 ft
- DOLLAR GENERAL STORE 14200Brownfields · 1200 ft
- Ken Richardt Trckng& ExcvatngUnderground Storage Tanks · 1800 ft
- 545 RUSSELL AVE SITESuperfund · 1900 ft
- SUPERFUND EMERGENCY CLEANUPBrownfields · 1900 ft
- Cheneys Auto CenterUnderground Storage Tanks · 1900 ft
- Old Public Works GarageUnderground Storage Tanks · 0.6 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Winthrop Harbor'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 Winthrop Harbor.
Sources Checked
within ~10 miles of Winthrop Harbor
Severity Distribution
within ~10 miles of Winthrop Harbor
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Winthrop Harbor, two things run higher than the national average within ~10 miles of Winthrop Harbor — Superfund (22 sites) and Toxics Release Inventory (79 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
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 Winthrop Harbor
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 Winthrop Harbor average
Your land is one point inside Winthrop Harbor
Everything above resolves to Winthrop Harbor 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 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 Winthrop Harbor Average
Winthrop Harbor Average
- ●USDA Zones 6a, averaged across Winthrop Harbor
- ●One soil character for all of Winthrop Harbor
- ●Frost dates read at Winthrop Harbor's scale: Apr 8 to Nov 6
YOUR Parcel
- ✓Your exact zone, not Winthrop Harbor's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Winthrop Harbor
Pull a site-specific report for your exact address in Winthrop Harbor, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Winthrop Harbor averages can't show:
We read public map data around Winthrop Harbor — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Winthrop Harbor average
How we know this about Winthrop Harbor
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 Winthrop Harbor’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 Winthrop Harbor
When does frost risk typically end in Winthrop Harbor?
The last hard freeze (28°F) in Winthrop Harbor typically lands around Apr 8, 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 29.
When is the first frost in Winthrop Harbor?
The first hard freeze (28°F) in Winthrop Harbor typically arrives around Nov 6, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 23, so the watching starts about Oct 7 — about 212 days after the spring freeze cleared.
How long is the growing season in Winthrop Harbor?
Measured between 28°F hard freezes, Winthrop Harbor sees about 212 frost-free days — roughly Apr 8 through Nov 6, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 29 to Oct 23, about 177 days.
Is the soil safe to grow vegetables in Winthrop Harbor?
The federal record around Winthrop Harbor runs heavier than most — 1,284 documented sites, mostly Underground Storage Tanks entries (674), the nearest PFAS record about 0.1 miles out — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.
How do I protect my plants from frost in Winthrop Harbor?
From about Oct 7 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 6 (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 6. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Winthrop Harbor's scale — its 6a band and its 212-day season. Your yard writes its own version of Winthrop Harbor'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 Winthrop Harbor’s own scale
7 of the readings below were taken at Winthrop Harbor's own scale — its own ~212-day season between 28°F freezes, the 2,977 acres it covers and 1,284 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Winthrop Harbor's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Winthrop Harbor's own 28°F hard-freeze dates, about Apr 8 and Nov 6 and the ~212-day span between themNOAA 1991–2020 Climate Normals
- 1,284 documented contamination sites on the federal record near Winthrop Harbor, the closest PFAS record about 0.1 miles out from the town centreFederal environmental registers
- Winthrop Harbor's boundary and the 2,977 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~212-day seasonGrowable Ground crop-matching engine
- Winthrop Harbor sits in the Central Corn Belt Plains — not the ecoregion its county mostly readsUS EPA Level III Ecoregions
- A documented spotted-lanternfly record within reach of Winthrop Harborlydemapr (De Bona & Helmus), 10 km survey lattice
Inherited from a wider read
- Soil character — no town-scale survey exists, so Winthrop Harbor's 2,977 acres read through its county's SSURGO summaryfrom Lake County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Lake 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 Lake County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Winthrop Harbor's 2,977 acreswhy one lot differs from the next →
- Which side of Winthrop Harbor you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 2,977 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest PFAS 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 Winthrop Harbor-wide figureread your own land →