Yes — Strong Match
viola 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 ~70 viola needs.
Sow by about Aug 23
Viola is grown as an annual, so what decides it here is season length, not a winter zone. It needs about 70 days from sowing to finish and a typical Illinois season runs ~212 frost-free days, leaving 142 days of slack. That is room to sow as late as about Aug 23 and still finish before the usual first freeze (Nov 1), or to run a second succession.
Want more weeks at either end of that window? How to buy the weeks →
70 days to maturity against Illinois’s ~212-day season. NOAA Regional Climate Centers ACIS 1991-2020 (28°F killing freeze), state median across counties, via stateClimateData.ts.
Your yard isn't the whole zone.
Viola is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical Illinois site runs ~212 frost-free days, but that is a state median, not your yard: slope, trees, and low spots move the last-frost date across a single parcel. Enter your address and we'll score viola against your land's actual frost dates, sun, and soil.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Zone Comparison
Viola Needs
- USDA Zones: Data pending
- Sun: Part Sun
- Mature size: 9 in 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
Preferred Soil pH
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Viola 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 viola goes out, not when it starts. It is sown under cover about 10 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.
Days to maturity vs. the window
At 70 days to maturity (USDA PLANTS Database), counting from the last hard freeze it ripens with 133 days to spare even in Illinois's tightest freeze scenario — room for a later start or a second sowing.
Timing tuned to sub-state frost dates — Jo Daviess County, not the statewide average.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: USDA PLANTS Database. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
Days to maturity
Viola matures in ~70 days (Growable Ground Plant Database). A typical Illinois site has ~212 frost-free days, so plenty of room for a second succession.
Growing degree days
Viola needs ~600 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
Viola likes near-neutral soil (pH 5.4-6.5). That's the common-ground band across Illinois's prairie loam and silt loam — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 5.4 and 5.8 — 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
Illinois's soils run mostly silt loam, but SSURGO maps the series, texture, and drainage under your exact parcel. What matters for viola is the horizon its roots actually work, not the surface. That map unit, not the state average, decides how viola performs.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Illinois soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Viola in Illinois — Quick Answer
- Verdict: Yes — Strong Match
- Plant Zones: Data pending (USDA PLANTS Database)
- State Zones: 5a-7b (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 29 - Apr 8 to Oct 28 - Nov 5 (NOAA Regional Climate Centers ACIS, 1991-2020)
- Days to Maturity: 70 days
What Else to Consider for Viola 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 viola here specifically
Illinois's soils run mostly silt loam (Alfisols), and whether that suits viola's pH 5.4–6.5 preference comes down to your exact parcel, not the statewide picture.
Pull your parcel's SSURGO map unit, test pH, and amend toward viola's 5.4–6.5 target before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Illinois grower, not just viola — 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 viola to your county's window, not the statewide date.
Viola needs about 70 days of frost-free season from planting to harvest. Even Jo Daviess County — Illinois’s shortest season at 177 frost-free days — clears that by 107 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 viola about 142 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"). Viola's 70-day requirement: USDA PLANTS / Growable Ground plant database (days to maturity). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
Viola draws honeybees and native bees (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, viola 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 Viola Varieties for Illinois
Illinois publishes no state variety trial for viola, 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 viola, the canonical source is University of Illinois Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Viola native to Illinois?
No — the USDA PLANTS Database lists Viola 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 Viola in Illinois
When can I plant Viola 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.
Can Viola mature before first frost in Illinois?
Yes — Viola matures in 70 days (USDA PLANTS Database), and Illinois's dependable hard-freeze-free window runs 203 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 133 days of margin. Plant once the last hard freeze has passed — two to three weeks later for anything tender — and it ripens ahead of the first fall freeze.
What hardiness zone is Viola grown in across Illinois?
Illinois spans USDA hardiness zones 5a-7b (USDA ARS PHZM 2023). Viola carries a range of zones Data pending, 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). Viola 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. In cooler counties like Jo Daviess, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Viola native to Illinois?
No — the USDA PLANTS Database lists Viola 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 Viola in Illinois?
Viola prefers pH 5.4-6.5 and well (dry spells) drainage (Growable Ground Plant Database). That sits in the common-ground band across Illinois soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Viola actually grow on my specific land in Illinois?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores viola 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 viola against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Illinois viola 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 viola average
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
Last updated: