USDA zone 6b in Illinois
USDA plant hardiness zone 6b covers 43 locations across Illinois (average annual extreme minimum −5 to 0 °F): Albion, IL, Bethalto, IL, Bone Gap, IL, Carlinville, IL, Casey, IL, Centralia, IL, and 37 more. Average last spring frost across this group ranges April 2 (Bone Gap) to April 20 (Hardin), and growing seasons run 181–214 days (Hardin to Bethalto) — 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 Sumner, this group's median-season location.
- USDA zone
- 6b−5 to 0 °F
- Last frost range
- Apr 2–Apr 20avg, 32°F
- First frost range
- Oct 19–Nov 5avg, 32°F
- Growing season range
- 181–214days
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) |
|---|---|---|---|---|---|
| Albion | Browns | Albion | Apr 4 | Oct 28 | 206 |
| Bethalto | Bunker Hill, Hamel, Worden, Moro, Prairietown | Alton - Melvin Price L&d | Apr 4 | Nov 5 | 214 |
| Bone Gap | Bellmont, Keensburg | Mt Carmel | Apr 2 | Oct 31 | 209 |
| Carlinville | Gillespie, Palmyra, Chesterfield, Royal Lakes | Carlinville | Apr 14 | Oct 21 | 188 |
| Casey | Martinsville | Casey | Apr 14 | Oct 20 | 187 |
| Centralia | Dix, Irvington, Kell, Woodlawn, Walnut Hill | Iuka 12 Sw | Apr 9 | Oct 24 | 196 |
| Chicago | — | Chicago Northerly Is | Apr 10 | Nov 5 | 208 |
| Chicago | — | Chicago Midway Ap | Apr 11 | Oct 31 | 201 |
| Coulterville | — | Sparta 1 W | Apr 12 | Oct 22 | 191 |
| Effingham | Teutopolis, Altamont, Mason, Watson, Edgewood, Beecher, +4 more | Effingham 3sw | Apr 13 | Oct 24 | 191 |
| Enfield | — | Carmi 3 | Apr 15 | Oct 19 | 183 |
| Ewing | Hanaford, Macedonia | Benton 2 N | Apr 4 | Oct 28 | 206 |
| Fairfield | Wayne, Sims, Jeffersonville, Mill Shoals, Cisne, Mount Erie, +2 more | Fairfield Radio Wfiw | Apr 7 | Oct 26 | 201 |
| Flora | Clay, Louisville, Xenia, Sailor Springs, Johnsonville | Flora | Apr 9 | Oct 24 | 198 |
| Godfrey | Grafton, Elsah, Brussels | St Charles Co Ap | Apr 5 | Oct 27 | 203 |
| Greenup | — | Charleston | Apr 15 | Oct 23 | 187 |
| Hardin | Batchtown, Elsberry, Winfield, Old Monroe, Foley, Eldred, +2 more | Elsberry 1 S | Apr 20 | Oct 20 | 181 |
| Highland | Carlyle, Breese, Aviston, Albers, Pocahontas, Pierron, +4 more | Carlyle Rsvr | Apr 6 | Oct 29 | 204 |
| Hillview | — | White Hall 1 E | Apr 13 | Oct 22 | 190 |
| Hull | Saverton, New Canton, Ashburn | Saverton L&d 22 | Apr 4 | Nov 4 | 212 |
| Jerseyville | Brighton, Elsah, Rockbridge, Kane, Medora, Fieldon, +1 more | Jerseyville 2 Sw | Apr 14 | Oct 19 | 187 |
| Lawrenceville | Flat Rock | Lawrenceville Intl Ap | Apr 8 | Oct 26 | 200 |
| Litchfield | Staunton, Witt, Coffeen, Benld, Taylor Springs, New Douglas, +12 more | Hillsboro | Apr 13 | Oct 24 | 192 |
| Mascoutah | Scott AFB, Lebanon, Trenton, New Baden, Lenzburg, St. Libory, +3 more | Belleville Siu Rsch | Apr 12 | Oct 20 | 189 |
| McLeansboro | Broughton | Mcleansboro | Apr 11 | Oct 21 | 190 |
| Mount Vernon | Ina, Bluford, Bonnie, Waltonville, Belle Rive, Ewing, +4 more | Mt Vernon 3 Ne | Apr 11 | Oct 22 | 193 |
| Nashville | Okawville, Oakdale, Richview, Ashley, Du Bois, Radom, +2 more | Nashville 1 E | Apr 7 | Oct 26 | 201 |
| Neoga | Strasburg | Windsor | Apr 16 | Oct 22 | 187 |
| Newton | Dieterich, Ste. Marie, Oblong, Willow Hill, Jewett, Montrose, +5 more | Newton | Apr 13 | Oct 22 | 190 |
| Olney | West Salem, Noble, Calhoun, Parkersburg, Claremont, Dundas | Olney 2s | Apr 15 | Oct 23 | 189 |
| Pana | Tower Hill, Oconee, Ohlman | Pana | Apr 17 | Oct 23 | 188 |
| Ramsey | Fillmore, Cowden, Herrick, Bingham | Ramsey | Apr 15 | Oct 19 | 185 |
| Raymond | — | Morrisonville | Apr 12 | Oct 20 | 190 |
| Robinson | Stoy | Robinson | Apr 13 | Oct 22 | 190 |
| Salem | Kinmundy, Alma, Patoka, Odin, Sandoval, Iuka | Salem | Apr 9 | Oct 26 | 197 |
| Stewardson | Lakewood | Shelbyville Dam | Apr 10 | Oct 24 | 195 |
| Sumner * | Bridgeport, St. Francisville, Allendale | Lawrenceville 2wsw | Apr 12 | Oct 25 | 193 |
| Thompsonville | — | Harrisburg | Apr 7 | Oct 26 | 202 |
| Toledo | Trilla | Mattoon Coles Co Ap | Apr 15 | Oct 24 | 189 |
| Vandalia | Greenville, St. Elmo, Mulberry Grove, Smithboro, Vernon, Brownstown, +1 more | Vandalia | Apr 10 | Oct 24 | 196 |
| Virden | Girard, Modesto, Nilwood | Virden | Apr 7 | Oct 29 | 205 |
| Waltonville | Sesser, Tamaroa | Du Quoin 4 Se | Apr 6 | Oct 22 | 199 |
| West Union | Palestine, Hutsonville, Merom, Annapolis, West York | Palestine | Apr 12 | Oct 22 | 193 |
* Sumner 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 (Sumner, representative)
Computed from Sumner's average frost dates — the median-season location in this Illinoiszone 6b 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 15 – Mar 1 | Apr 19 – Apr 26 | Jun 18 – Jul 8 | — | matures comfortably |
| Pepper | Very tender | Feb 1 – Feb 15 | Apr 26 – May 3 | Jun 25 – Jul 25 | — | matures comfortably |
| Cucumber | Tender | Mar 15 – Mar 22 | Apr 19 – Apr 26 | Jun 8 – Jun 28 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | Apr 19 – Apr 26 | Jun 3 – Jun 18 | — | matures comfortably |
| Bush bean | Tender | — | Apr 19 – Apr 26 | Jun 8 – Jun 18 | Aug 26 – Sep 5 | matures comfortably |
| Sweet corn | Tender | — | Apr 12 – Apr 26 | Jun 11 – Jul 11 | — | matures comfortably |
| Basil | Very tender | Mar 1 – Mar 15 | Apr 19 – Apr 26 | May 19 – Jun 3 | — | matures comfortably |
| Lettuce | Half-hardy | Mar 1 – Mar 15 | Mar 15 – Mar 29 | Apr 29 – May 14 | Aug 12 – Aug 27 | matures comfortably |
| Pea | Hardy | — | Mar 1 – Mar 15 | Apr 25 – May 10 | Aug 2 – Aug 17 | matures comfortably |
| Spinach | Hardy | — | Mar 1 – Mar 15 | Apr 10 – Apr 20 | Aug 22 – Sep 1 | matures comfortably |
| Carrot | Half-hardy | — | Mar 22 – Mar 29 | May 21 – Jun 10 | Jul 23 – Aug 12 | matures comfortably |
| Broccoli | Half-hardy | Feb 15 – Mar 1 | Mar 15 – Mar 29 | May 9 – May 29 | Jul 28 – Aug 17 | matures comfortably |
Which crops fit this growing season
Using Sumner's own 193-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 (Sumner)
From NOAA's 1991–2020 Climate Normals at station USC00114957. 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 24 | May 10 | Oct 16 | Oct 27 | 171 |
| 32°F (freeze) | Apr 12 | Apr 30 | Oct 25 | Nov 5 | 193 |
| 28°F | Apr 1 | Apr 17 | Nov 3 | Nov 20 | 214 |
| 24°F | Mar 22 | Apr 5 | Nov 14 | Dec 3 | 239 |
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 43 locations is 3,944; Sumner's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 3,971 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 6,430 | cool-season crops (brassicas, greens) |
Hardiness zone 6b in Illinois
Zone 6b means an average annual extreme minimum winter temperature of about −5 to 0 °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, 6a, 7a.
Explore zone 6b in other states at zone 6b, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 6b mean in Illinois?
- Zone 6b means an average annual extreme minimum winter temperature of −5 to 0 °F — the standard USDA measure of which perennials survive winter. 43 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 6b is the growing season longest?
- Bethalto runs the longest season on this page at about 214 days; Hardin is shortest at about 181 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 6b?
- Using Sumner's frost dates (this page's median-season location): start seeds indoors about Feb 15 – Mar 1, then transplant outside about Apr 19 – Apr 26. 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 6b 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 43 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.