USDA zone 6a in Illinois
USDA plant hardiness zone 6a covers 66 locations across Illinois (average annual extreme minimum −10 to −5 °F): Arlington Heights, IL, Arlington Heights, IL, Assumption, IL, Auburn, IL, Barry, IL, Beardstown, IL, and 60 more. Average last spring frost across this group ranges April 4 (Kinderhook) to April 30 (Waukegan), and growing seasons run 170–212 days (Farmer to Kinderhook) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Illinois location's own frost dates; the printable planting calendar uses Charleston, this group's median-season location.
- USDA zone
- 6a−10 to −5 °F
- Last frost range
- Apr 4–Apr 30avg, 32°F
- First frost range
- Oct 12–Nov 5avg, 32°F
- Growing season range
- 170–212days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Arlington Heights | Glenview, Northbrook, Mount Prospect, Buffalo Grove, Wheeling, Lincolnshire, +2 more | Chicago Palwaukee Ap | Apr 19 | Oct 26 | 190 |
| Arlington Heights | Des Plaines, Elk Grove, Elmhurst, Addison, Park Ridge, Niles, +17 more | Chicago Ohare Intl Ap | Apr 16 | Oct 28 | 193 |
| Assumption | Owaneco | Pana | Apr 17 | Oct 23 | 188 |
| Auburn | Waverly, Divernon, Thayer | Virden | Apr 7 | Oct 29 | 205 |
| Barry | Mount Sterling, Griggsville, New Salem, Versailles, Meredosia, Mound Station, +2 more | Perry 6 Nw | Apr 18 | Oct 15 | 179 |
| Beardstown | Rushville, Vermont, Littleton, Camden, Astoria, Industry, +5 more | Rushville | Apr 16 | Oct 23 | 189 |
| Bloomington | Normal, Twin Grove, Heyworth, Downs, Le Roy, Hudson, +6 more | Normal 4ne | Apr 25 | Oct 16 | 172 |
| Burr Ridge | Hinsdale, Western Springs | Little Red School Hse | Apr 19 | Oct 22 | 183 |
| Bushnell | Prairie, Bardolph, Smithfield, Marietta, Ellisville | Prairie City 2s | Apr 17 | Oct 22 | 185 |
| Camp Point | Clayton, Mendon, Liberty, Paloma, Plainville, Fowler, +1 more | Quincy Rgnl Ap | Apr 14 | Oct 23 | 191 |
| Carthage | Ferris, Loraine, Augusta, Plymouth, Bowen, Tennessee, +2 more | Bentley | Apr 13 | Oct 22 | 191 |
| Champaign | Urbana, St. Joseph, Lake of the Woods | Champaign 3s | Apr 15 | Oct 24 | 190 |
| Charleston * | Westfield, Ashmore, Oakland | Charleston | Apr 15 | Oct 23 | 187 |
| Chatsworth | Piper, Strawn, Thawville | Piper City | Apr 25 | Oct 20 | 175 |
| Chicago | Orland Park, Oak Lawn, Alsip, Palos Park, Palos Hills, Willow Springs, +16 more | Chicago Midway Ap 3sw | Apr 10 | Nov 1 | 203 |
| Chicago | Westchester, Maywood, La Grange Park, Whiting, Broadview | Chicago Midway Ap | Apr 11 | Oct 31 | 201 |
| Chicago | Lincolnwood | Chicago Northerly Is | Apr 10 | Nov 5 | 208 |
| Chillicothe | Metamora, Rome | Lacon | Apr 20 | Oct 17 | 178 |
| Danville | Tilton, Westville, Oakwood, Catlin, Alvan (Alvin), Bismarck, +4 more | Danville | Apr 21 | Oct 20 | 181 |
| Decatur | Mount Zion, Forsyth, Moweaqua, Harristown, Maroa, Macon, +17 more | Decatur Wtp | Apr 14 | Oct 24 | 192 |
| Farmer | Mansfield, De Land, White Heath | Champaign 9 Sw | Apr 23 | Oct 13 | 170 |
| Fidelity | — | Jerseyville 2 Sw | Apr 14 | Oct 19 | 187 |
| Gibson | Saybrook, Sibley, Bellflower, Anchor, Foosland | Gibson City | Apr 21 | Oct 17 | 178 |
| Golden | La Prairie | Golden | Apr 18 | Oct 21 | 187 |
| Havana | Lewistown, Goofy Ridge, Kilbourne, Cuba, Bryant, Easton, +1 more | Havana | Apr 17 | Oct 19 | 185 |
| Hettick | — | Carlinville | Apr 14 | Oct 21 | 188 |
| Homer | Sidell, Allerton, Indianola, Broadlands, Fairmount | Sidell 4n | Apr 19 | Oct 19 | 181 |
| Hoopeston | Henning, Rossville, Cissna Park, Milford, Rankin, Potomac, +2 more | Hoopeston | Apr 22 | Oct 19 | 180 |
| Jacksonville | Virginia, Chapin, Alexander, Franklin, Chandlerville, Arenzville, +3 more | Jacksonville 2e | Apr 19 | Oct 17 | 179 |
| Joliet | New Lenox, Elwood, Manhattan, Ingalls Park, Ridgewood | Joliet Brandon Rd Dam | Apr 19 | Oct 25 | 188 |
| Joliet | Bolingbrook, Homer Glen, Orland Park, Romeoville, Lockport, Mokena, +1 more | Romeoville Wfo | Apr 20 | Oct 22 | 184 |
| Kampsville | Hamburg | Elsberry 1 S | Apr 20 | Oct 20 | 181 |
| Kinderhook | New London, Frankford | Saverton L&d 22 | Apr 4 | Nov 4 | 212 |
| Lake Forest | Glenview, Highland Park, Skokie, Evanston, Wilmette, Morton Grove, +3 more | Chicago Botanic Garden | Apr 26 | Oct 21 | 176 |
| Lexington | Fairbury, Colfax, Anchor | Chenoa | Apr 23 | Oct 15 | 174 |
| Libertyville | Vernon Hills | Mundelein 4 Wsw | Apr 29 | Oct 20 | 172 |
| Lincoln | Clinton, Elkhart, Delavan, Atlanta, McLean, Mount Pulaski, +12 more | Lincoln | Apr 20 | Oct 16 | 179 |
| Lomax | Carman | Burlington 2s | Apr 18 | Oct 20 | 185 |
| Macomb | Dallas, La Harpe, Colchester, Blandinsville, Stronghurst | La Harpe | Apr 21 | Oct 19 | 180 |
| Mason | — | Mason City 4se | Apr 17 | Oct 18 | 182 |
| Mattoon | Humboldt, Janesville | Mattoon Coles Co Ap | Apr 15 | Oct 24 | 189 |
| Monticello | Savoy, Tolono, Sadorus, Philo, Ivesdale, Seymour | Champaign Willard Ap | Apr 19 | Oct 17 | 180 |
| Naperville | Downers Grove, Lombard, Woodridge, Oak Brook, Darien, Westmont, +1 more | Wheaton 3 Se | Apr 27 | Oct 17 | 173 |
| Nebo | — | Clarksville L&d 24 | Apr 4 | Nov 1 | 208 |
| Paris | Marshall, St. Bernice, Kansas, Chrisman, Metcalf, Brocton, +8 more | Paris Stp | Apr 21 | Oct 20 | 179 |
| Paxton | Loda, Elliott, Roberts, Melvin, Buckley | Paxton 2 Wsw | Apr 23 | Oct 12 | 170 |
| Peoria | East Peoria, Pekin, Morton, Canton, Bartonville, Creve Coeur, +13 more | Peoria Gtr Peoria Ap | Apr 16 | Oct 23 | 189 |
| Petersburg | Oakford | Petersburg 1e | Apr 13 | Oct 21 | 189 |
| Pittsfield | Milton | Pittsfield #2 | Apr 14 | Oct 21 | 189 |
| Pontiac | Odell, Forrest | Pontiac | Apr 16 | Oct 24 | 191 |
| Quincy | Palmyra, Ewing | Quincy Dam 21 | Apr 8 | Oct 30 | 204 |
| Rantoul | Fisher, Thomasboro, Gifford, Ludlow, Penfield, Royal, +1 more | Rantoul | Apr 21 | Oct 18 | 179 |
| Ridge Farm | Veedersburg, Georgetown, Covington, Cayuga, Kingman, Perrysville | Perrysville 4 Wnw | Apr 23 | Oct 14 | 171 |
| Shelbyville | Findlay | Shelbyville Dam | Apr 10 | Oct 24 | 195 |
| Sidney | Ogden | Ogden | Apr 20 | Oct 21 | 182 |
| Springfield | Chatham, Sherman, Rochester, Athens, Williamsville, Pleasant Plains, +11 more | Springfield Capital Ap | Apr 14 | Oct 20 | 187 |
| Sullivan | Bethany | Sullivan 3s | Apr 15 | Oct 22 | 187 |
| Taylorville | Pawnee, Nokomis, Morrisonville, Palmer, Kincaid, Harvel, +5 more | Morrisonville | Apr 12 | Oct 20 | 190 |
| Tuscola | Arcola, Villa Grove, Arthur, Camargo, Bement, Atwood, +4 more | Tuscola | Apr 15 | Oct 20 | 188 |
| Wapella | De Witt | Bloomington 5w | Apr 21 | Oct 20 | 181 |
| Warsaw | Mooar, Kahoka, Elvaston, Wayland, Argyle, Revere | Keokuk Lock Dam 19 | Apr 10 | Oct 27 | 198 |
| Washington | Mackinaw, Minier | Congerville 2nw | Apr 21 | Oct 17 | 178 |
| Waukegan | Gurnee, Zion, North Chicago, Winthrop Harbor, Lake Bluff | Chicago Waukegan Rgnl Ap | Apr 30 | Oct 21 | 173 |
| White Hall | Carrollton, Greenfield, Pearl, Roodhouse, Manchester, Wilmington, +2 more | White Hall 1 E | Apr 13 | Oct 22 | 190 |
| Winchester | Exeter | Winchester | Apr 18 | Oct 20 | 183 |
| Windsor | Gays | Windsor | Apr 16 | Oct 22 | 187 |
* Charleston is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Charleston, representative)
Computed from Charleston's average frost dates — the median-season location in this Illinoiszone 6a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Feb 18 – Mar 4 | Apr 22 – Apr 29 | Jun 21 – Jul 11 | — | matures comfortably |
| Pepper | Very tender | Feb 4 – Feb 18 | Apr 29 – May 6 | Jun 28 – Jul 28 | — | matures comfortably |
| Cucumber | Tender | Mar 18 – Mar 25 | Apr 22 – Apr 29 | Jun 11 – Jul 1 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | Apr 22 – Apr 29 | Jun 6 – Jun 21 | — | matures comfortably |
| Bush bean | Tender | — | Apr 22 – Apr 29 | Jun 11 – Jun 21 | Aug 24 – Sep 3 | matures comfortably |
| Sweet corn | Tender | — | Apr 15 – Apr 29 | Jun 14 – Jul 14 | — | matures comfortably |
| Basil | Very tender | Mar 4 – Mar 18 | Apr 22 – Apr 29 | May 22 – Jun 6 | — | matures comfortably |
| Lettuce | Half-hardy | Mar 4 – Mar 18 | Mar 18 – Apr 1 | May 2 – May 17 | Aug 10 – Aug 25 | matures comfortably |
| Pea | Hardy | — | Mar 4 – Mar 18 | Apr 28 – May 13 | Jul 31 – Aug 15 | matures comfortably |
| Spinach | Hardy | — | Mar 4 – Mar 18 | Apr 13 – Apr 23 | Aug 20 – Aug 30 | matures comfortably |
| Carrot | Half-hardy | — | Mar 25 – Apr 1 | May 24 – Jun 13 | Jul 21 – Aug 10 | matures comfortably |
| Broccoli | Half-hardy | Feb 18 – Mar 4 | Mar 18 – Apr 1 | May 12 – Jun 1 | Jul 26 – Aug 15 | matures comfortably |
Which crops fit this growing season
Using Charleston's own 187-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Charleston)
From NOAA's 1991–2020 Climate Normals at station USC00111436. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | Apr 27 | May 15 | Oct 12 | Oct 25 | 165 |
| 32°F (freeze) | Apr 15 | May 3 | Oct 23 | Nov 4 | 187 |
| 28°F | Apr 3 | Apr 20 | Nov 2 | Nov 16 | 213 |
| 24°F | Mar 25 | Apr 10 | Nov 13 | Dec 2 | 236 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 66 locations is 3,558; Charleston's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 4,056 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 6,513 | cool-season crops (brassicas, greens) |
Hardiness zone 6a in Illinois
Zone 6a means an average annual extreme minimum winter temperature of about −10 to −5 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Illinois spans 5 hardiness zones in this dataset — see all Illinois locations for the full range, including zones5a, 5b, 6b, 7a.
Explore zone 6a in other states at zone 6a, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 6a mean in Illinois?
- Zone 6a means an average annual extreme minimum winter temperature of −10 to −5 °F — the standard USDA measure of which perennials survive winter. 66 locations in Illinois fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Illinois's zone 6a is the growing season longest?
- Kinderhook runs the longest season on this page at about 212 days; Farmer is shortest at about 170 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Illinois's zone 6a?
- Using Charleston's frost dates (this page's median-season location): start seeds indoors about Feb 18 – Mar 4, then transplant outside about Apr 22 – Apr 29. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Illinois's zone 6a have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 66 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.