Generally — Most Areas
autumn fern (zones 6-8) suits most of Illinois (5a-7b) — zones 6-7 are in range, and the rest of the state is the exception.
Autumn Fern in Illinois — the short answer
Autumn Fern in Illinois: hardy in zones 6–8, part sun, against a state median of ~212 frost-free days.
- Plant zones
- 6-8
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- Illinois zones
- 5a-7b
- USDA PHZM 2023
- Frost window
- Mar 29 - Apr 8 – Oct 28 - Nov 5
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 177 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — per-field provenance varies and is published with the dataset.
Your yard isn't the whole zone.
Illinois spans zones 5a-7b, but your yard has its own microclimate — slope, trees, and low spots shift frost and sun across a single parcel. Enter your address and we'll score autumn fern against your land's actual soil, sun, and frost.
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Illinois is not one climate
A single Illinois answer averages 102 counties whose growing seasons are 67 days apart — from 177 frost-free days in Jo Daviess County to 244 in Alexander County. Which end of that your land sits nearer changes what autumn fern can finish before the first hard freeze.
The middle half of 102 counties runs 203–221 days, with a median of 212 days — a 67-day span end to end.
Measured across 102 Illinois counties. NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze. Quartiles are order statistics — every figure shown is a value a real county recorded, not an interpolation. Your own site sits somewhere inside this range; a parcel report resolves where.
Where in Illinois Fits Best
Autumn Fern is rated for zones 6–8 — a cold floor USDA puts at -10 to 0°F. Against Illinois’s 102 counties that band holds in 74 of them, and the line runs at Adams County (zone 6a), the coldest county still inside it.
Inside zones 6–8
74 counties
- Brown County · zone 6a
- Cass County · zone 6a
- Champaign County · zone 6a
3 of 74 shown
Below the zone 6 floor
28 counties
- Carroll County · zone 5a
- Jo Daviess County · zone 5a
- Stephenson County · zone 5a
3 of 28 shown
Winter cold is the limit here — the same plant works in a container that comes under cover.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. A zone is a 10°F band of average annual extreme minimum temperature, so the floor above is the band the plant's rating denotes, not a single measured kill point. Slope, shelter and cold-air drainage routinely move a site half a zone either way from its county figure — which is the part only your address resolves.
Even within Illinois's zones 5a-7b, county microclimates differ enough to change what thrives. These counties carry the closest zone match for autumn fern (USDA PHZM 2023):
Zone Comparison
Autumn Fern Needs
- USDA Zones: 6-8
- Sun: Part Sun
- Mature size: 2 ft tall
- Drought tolerance: Low
Illinois Has
- USDA Zones: 5a-7b
- Last Hard Freeze (28°F): Mar 29 - Apr 8
- First Hard Freeze (28°F): Oct 28 - Nov 5
- Annual Rainfall: 34-48 inches
- Common Soils: Prairie loam, Silt loam, Clay loam
Plant Zone Range (zones 6-8)
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS, and university Extension sources — per-field provenance varies and is published with the dataset. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Autumn Fern in Illinois
The frost window
Across Illinois, the last spring hard freeze (28°F) clears between Mar 29 and Apr 8, and the first fall hard freeze lands between Oct 28 and Nov 5 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 203-day window you can count on — up to 221 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: Growable Ground Plant Database — frost-free days from FAO ECOCROP, days to harvest from university Extension production guides, and growing-degree-day and chill-hour minimums that are compilation estimates rather than published figures. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Soil + Drainage Fit
Drainage requirement: poorly (saturated >50% of year). A soil-survey lookup (NRCS SSURGO) flags whether your specific site matches.
Plant pH requirements: FAO ECOCROP and USDA PLANTS, with the remaining rows from other published sources or Growable Ground compilation. Drainage: FAO ECOCROP, with the remaining rows from other published sources or Growable Ground compilation. Illinois soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
What Else to Consider for Autumn Fern in Illinois
Zone compatibility tells you about winter cold survival — but Illinois growers also need to think about:
Heavy clay soils in northern IL drain poorly
Extreme temperature swings between summer and winter
Japanese beetles are a major garden pest
What to actually do about these — and the constraints that apply to every Illinois grower, not just autumn fern — is covered on the Illinois growing guide.
Where in Illinois Autumn Fern Is Zone-Hardy
Autumn Fern is rated for USDA zones 6–8. 74 of Illinois’s 102 counties fall inside that band. The coldest that does is Adams County at zone 6a. 28 counties sit below the plant’s zone 6 floor, where an unprotected plant is relying on snow cover and a mild year. Where you are in Illinois decides this one.
Across those 102 counties Illinois’s winter-low ladder runs from zone 5a in Carroll County to zone 7a in Williamson County — 2 USDA zones of spread, which is 20°F between the two counties’ average coldest night of the year. That is why a statewide hardiness answer is where you start and not where you finish.
The planting window moves with it. Jo Daviess County holds its last hard freeze (28°F) until about Apr 22, while Alexander County is clear by Mar 17 — 36 days apart. Set autumn fern out on your county’s date, not the state’s.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. County last-freeze dates: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F killing freeze — earlier than the folk 32°F "last frost". Autumn Fern’s zone 6–8 band: USDA PLANTS / Growable Ground plant database. A parcel report resolves your address’s own zone and frost dates rather than its county’s.
Illinois Cooperative Extension
For Illinois-specific cultivar recommendations, planting calendars, and pest pressure for autumn fern, the canonical source is University of Illinois Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Common Questions About Growing Autumn Fern in Illinois
When can I plant Autumn Fern in Illinois?
Illinois's last spring hard freeze (28°F) clears between Mar 29 and Apr 8, and the first fall hard freeze lands between Oct 28 and Nov 5 (NOAA Regional Climate Centers ACIS, 1991-2020). Time outdoor planting to after the last hard freeze for your specific site — a further two to three weeks for anything tender — and count back from those dates for transplant scheduling.
What hardiness zone is Autumn Fern grown in across Illinois?
Illinois spans USDA hardiness zones 5a-7b (USDA ARS PHZM 2023). Autumn Fern carries a range of zones 6-8, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Illinois site have?
A typical Illinois site sees ~212 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Autumn Fern should be matched against that window, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Will Autumn Fern actually grow on my specific land in Illinois?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores autumn fern against your address's exact soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in Illinois
State-level data is a sketch. Your Growable Ground report scores autumn fern against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Illinois autumn fern averages can't show:
We read public map data around Illinois — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Illinois autumn fern average
Explore More
Growing guides for autumn fern
Explore Illinois county by county
Illinois carries 102 counties with their own USDA zone — a sample of the growing pages for autumn fern there:
Where else autumn fern grows
Autumn Fern's zone band crosses state lines — these are the states closest to Illinois in winter climate where it also has a page, plus the far ends of its range. Each one re-answers the question with that state's own record.
More to grow in Illinois
Illinois has a growing page for 893 plants — a rotating sample of the rest of the shelf.
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