Yes — Strong Match
purple basil is grown as an annual, so season length decides it here, not a winter zone — and Illinois's typical season runs ~212 frost-free days against the ~80 purple basil needs.
Sow by about Aug 23
Purple Basil is grown as an annual, so what decides it here is season length, not a winter zone. It needs about 80 frost-free days and a typical Illinois season runs ~212 frost-free days, leaving 132 days of slack. That is room to sow as late as about Aug 23 and still finish before the usual first freeze (Nov 1).
Want more weeks at either end of that window? How to buy the weeks →
80 frost-free days required against Illinois’s ~212-day season. NOAA Regional Climate Centers ACIS 1991-2020 (28°F killing freeze), state median across counties, via stateClimateData.ts.
Purple Basil in Illinois — the short answer
Purple Basil in Illinois: hardy in zones 10–11, full sun, against a state median of ~212 frost-free days.
- Plant zones
- 10-11
- Not verified
- 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
- Days to maturity
- 70 days
- Growable Ground Plant Database
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 sits in exactly one — and slope, tree cover, and cold-air pockets nudge it further. Enter your address and we'll score purple basil against your parcel's actual hardiness, soil, and sun.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
No card required · your parcel report in seconds — read in full free for your first 14 days
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 purple basil 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.
Zone Comparison
Purple Basil Needs
- USDA Zones: 10-11
- Frost-Free Days: 80+
- Sun: Full Sun
- Mature size: 1.5 ft tall
- Picking window: ~90 days of harvest
- 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 10-11)
Preferred Soil pH
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 Purple Basil 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.
When to start the seed
Those dates are when purple basil goes out, not when it starts. It is sown under cover about 6 weeks ahead, so counting back from Illinois's late-side last freeze of Apr 8 is what fixes your sowing date — and a yard that clears frost earlier than the state's late date starts earlier still.
Winter standing
Illinois runs as cold as USDA zone 5, and no sourced winter-hardiness floor is on record for purple basil, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether purple basil is a permanent planting or a replant-every-spring crop for you turns on your own zone within Illinois; check its hardiness range against that before treating it as long-lived ground.
Timing tuned to sub-state frost dates — Jo Daviess County, not the statewide average.
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.
Growing Season Fit
Frost-free days
Purple Basil wants 80+ frost-free days; a typical Illinois site sees ~212 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Purple Basil needs ~1500 GDD (base 50°F) to ripen. The state median runs ~3352 GDD (from PRISM 1991-2020 climate normals), so Illinois's typical season clears that easily.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
Purple Basil tolerates a wide pH range (pH 4.3-8.2) — 3.9 units, acid ground through alkaline — so soil acidity is rarely what limits it in Illinois. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 6 and 7 — worth knowing before you decide whether a Illinois soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Illinois site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
SSURGO maps about 52.0% of Illinois as poorly or somewhat-poorly drained, and the class flips parcel to parcel. Purple Basil has low drought tolerance, so it is the fast-draining end that will cost you — your soil map unit, not the state average, is the real answer.
Check your parcel → Source: USDA NRCS SSURGO.
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.
Before you plant purple basil for food
Anything you grow to eat takes up what is in the ground it grows in, so what is on record near you is worth knowing before purple basil goes in. What follows is Illinois’s documented federal record at state scale — a screening signal, not a soil test, and not a statement about any one lot.
Safe to Grow Here?
What the federal record shows across Illinois — and how to grow with it.
We checked the federal record across Illinois — 52,971 documented sites across 8 of the 8 source types we track.
The most significant on record: 622 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Illinois carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources Checked
across Illinois
Severity Distribution
across Illinois
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Illinois, two things run higher than the national average across Illinois — PFAS (482 sites) and Toxics Release Inventory (3,504 sites). That's not a problem with your land — it's information about it.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Toxics Release Inventory: TRI facilities report annual chemical releases to air, water, and land.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Check prevailing wind direction — downwind parcels face higher exposure than upwind or crosswind locations.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 8 federal source types.
What Else to Consider for Purple Basil 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
Growing purple basil here specifically
Purple Basil roots run shallow and prefer pH 4.3–8.2, but drainage comes first here: SSURGO maps about 52.0% of Illinois as poorly or somewhat-poorly drained, and wet ground rots its crown before pH ever matters.
Plant purple basil on a raised, gravel-amended berm so water drains fast and the crown stays dry. How to handle it →
What to actually do about these — and the constraints that apply to every Illinois grower, not just purple basil — is covered on the Illinois growing guide.
Timing shifts within Illinois
Illinois isn't one climate. In Jo Daviess County, the last hard freeze (28°F) holds until about Apr 22 — roughly 20 days later than the recorded state median — so plant purple basil to your county's window, not the statewide date.
Purple Basil needs about 80 days of frost-free season to complete its cycle. Even Jo Daviess County — Illinois’s shortest season at 177 frost-free days — clears that by 97 days, so season length isn’t the constraint anywhere in Illinois. What varies is your own parcel.
Across Illinois’s 102 counties the frost-free season runs from 177 days in Jo Daviess County to 244 days in Alexander County — a spread of 67 days, which is why a single statewide planting date misleads. The median Illinois county sees 212 frost-free days, leaving purple basil about 132 days of slack on a typical parcel — room for a second sowing where the season runs long.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). Purple Basil's 80-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
Purple Basil draws honeybees and native bees (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, purple basil can only work that bloom inside Illinois's frost window — roughly 212 days, opening after the last 28°F freeze (Mar 29 - Apr 8) and closing at the first (Oct 28 - Nov 5), per NOAA Regional Climate Centers ACIS, 1991-2020.
Recommended Purple Basil Varieties for Illinois
Illinois publishes no state variety trial for purple basil, so we won't invent a "best for Illinois" list. Choose types rated to your USDA hardiness zone (5a-7b), and confirm winter survival and drainage against your own parcel.
Illinois Cooperative Extension
For Illinois-specific cultivar recommendations, planting calendars, and pest pressure for purple basil, the canonical source is University of Illinois Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Purple Basil native to Illinois?
No — the USDA PLANTS Database lists Purple Basil as introduced rather than native in the Lower 48, so it is not part of Illinois's native flora. It grows here as a garden plant; pairing it with a few Illinois natives keeps local pollinators fed too.
Looking for plants that belong here? The Illinois growing guide lists USDA-documented natives for the state.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Purple Basil in Illinois
When can I plant Purple Basil 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). No sourced winter-hardiness floor is on record for Purple Basil, so this page does not state whether it overwinters in Illinois and publishes no fall establishment date for it — check its hardiness range against your own zone before treating it as a permanent planting.
What hardiness zone is Purple Basil grown in across Illinois?
Illinois spans USDA hardiness zones 5a-7b (USDA ARS PHZM 2023). Purple Basil carries a range of zones 10-11, 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). Purple Basil needs 80+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date. In cooler counties like Jo Daviess, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Purple Basil native to Illinois?
No — the USDA PLANTS Database lists Purple Basil as introduced rather than native in the Lower 48, so it is not part of Illinois's native flora. It grows here as a garden plant; pairing it with a few Illinois natives keeps local pollinators fed too.
How should I amend the soil for Purple Basil in Illinois?
Purple Basil tolerates pH 4.3-8.2 and well (dry spells) drainage (FAO ECOCROP). That is a 3.9-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Illinois site — amend for drainage and organic matter first.
Will Purple Basil actually grow on my specific land in Illinois?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores purple basil 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 purple basil against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Illinois purple basil 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 purple basil average
Explore More
Growing guides for purple basil
Explore Illinois county by county
Illinois carries 102 counties with their own USDA zone — a sample of the growing pages for purple basil there:
Where else purple basil grows
Purple Basil'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 889 plants — a rotating sample of the rest of the shelf.
Analysis by the Growable Ground research team, grounded in USDA PLANTS, USDA NRCS SSURGO, NOAA Climate Normals (1991-2020), and named Cooperative Extension sources. How we know →
Cite this dataset
Kirchick, M. (2026). Growable Ground Plant Database [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21435643
Licensed CC BY-NC 4.0. DOI 10.5281/zenodo.21435643
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