USDA zone 5b in Illinois
USDA plant hardiness zone 5b covers 57 locations across Illinois (average annual extreme minimum −15 to −10 °F): Aurora, IL, Avon, IL, Barrington Hills, IL, Bloomingdale, IL, Bondville, IL, Buffalo Prairie, IL, and 51 more. Average last spring frost across this group ranges April 8 (Oquawka) to May 1 (Crystal Lake), and growing seasons run 161–202 days (Oregon to Oquawka) — 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 LaSalle, this group's median-season location.
- USDA zone
- 5b−15 to −10 °F
- Last frost range
- Apr 8–May 1avg, 32°F
- First frost range
- Oct 7–Oct 29avg, 32°F
- Growing season range
- 161–202days
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) |
|---|---|---|---|---|---|
| Aurora | Naperville, Oswego, Batavia, Montgomery, North Aurora, Warrenville, +1 more | Aurora | Apr 19 | Oct 23 | 185 |
| Avon | — | Avon | Apr 22 | Oct 19 | 177 |
| Barrington Hills | Hoffman Estates, Schaumburg, Palatine, Fox River Grove | Barrington 3sw | Apr 25 | Oct 19 | 177 |
| Bloomingdale | Roselle | Streamwood | Apr 30 | Oct 13 | 163 |
| Bondville | — | Champaign Willard Ap | Apr 19 | Oct 17 | 180 |
| Buffalo Prairie | Aledo, Seaton, Viola, Hamlet, Windsor, Joy, +1 more | Aledo | Apr 22 | Oct 19 | 181 |
| Campton Hills | Bartlett, West Chicago, St. Charles, Wheaton, Geneva, Carol Stream, +2 more | West Chicago Dupage Ap | Apr 25 | Oct 19 | 174 |
| Carlock | — | Normal 4ne | Apr 25 | Oct 16 | 172 |
| Chenoa | Gridley | Chenoa | Apr 23 | Oct 15 | 174 |
| Crystal Lake | McHenry, Spring Grove, Cary, Prairie Grove, Lakemoor, Richmond, +6 more | Mc Henry -wg Stratton L&d | May 1 | Oct 11 | 162 |
| Cullom | Kempton | Piper City | Apr 25 | Oct 20 | 175 |
| DeKalb | Sycamore, Cortland, Maple Park, Waterman, Kirkland, Kingston, +1 more | De Kalb | Apr 24 | Oct 18 | 177 |
| Dixon | Amboy, Sterling, Rock Falls, Polo, Lee Center, Nachusa, +1 more | Dixon 1w | Apr 21 | Oct 19 | 180 |
| Dunlap | Princeville, Williamsfield, Wyoming, Bradford | Princeville | Apr 22 | Oct 14 | 174 |
| Dwight | Braceville, Gardner, Essex, Ransom, South Wilmington, Cabery, +7 more | Dwight | Apr 27 | Oct 15 | 170 |
| Elgin | Algonquin, Hampshire, Carpentersville, Streamwood, South Elgin, Burlington, +1 more | Elgin | Apr 26 | Oct 18 | 174 |
| Eureka | Goodfield, Congerville, Danvers, Deer Creek, Secor | Congerville 2nw | Apr 21 | Oct 17 | 178 |
| Galesburg | Oak Run, Fairview, Knoxville, Abingdon, East Galesburg, Oneida, +7 more | Galesburg | Apr 20 | Oct 19 | 180 |
| Galva | Cambridge, Williamsfield, Toulon, Altona, Woodhull, Bishop Hill, +2 more | Galva | Apr 26 | Oct 12 | 166 |
| Geneseo | Atkinson, Andover, Hooppole, Osco | Geneseo | Apr 20 | Oct 20 | 180 |
| Hennepin | Henry, Bureau Junction, Mark, McNabb | Hennepin Wtr Trmt Plt | Apr 24 | Oct 17 | 174 |
| Henry | Lacon, Washburn, Sparland, Lowpoint | Lacon | Apr 20 | Oct 17 | 178 |
| Hillcrest | Monroe Center, Creston, Ashton, Kings, Steward | Rochelle | Apr 26 | Oct 13 | 168 |
| Huntley | Woodstock, Belvidere, Marengo, Harvard, Genoa, Walworth, +3 more | Marengo | Apr 28 | Oct 12 | 166 |
| Joliet | Channahon, Lakewood Shores | Joliet Brandon Rd Dam | Apr 19 | Oct 25 | 188 |
| Kankakee | Bourbonnais, Bradley, Manteno, Hopkins Park, Aroma Park, Herscher, +4 more | Kankakee Metro Wastewater | Apr 19 | Oct 24 | 188 |
| Keithsburg | Wapello, Morning Sun, Oakville, Grandview, Eliza | New Boston Dam 17 | Apr 14 | Oct 24 | 190 |
| Kewanee | Annawan, Buda, Neponset, Bradford, Mineral | Kewanee 1 E | Apr 24 | Oct 17 | 175 |
| La Moille | Walnut, Ohio, Deer Grove, Tampico, Manlius, Harmon, +1 more | Walnut | Apr 24 | Oct 14 | 172 |
| Lane | — | Decatur Ap | Apr 16 | Oct 22 | 187 |
| LaSalle * | Peru, Oglesby, North Utica, Tonica, Granville, Ladd, +7 more | Peru | Apr 24 | Oct 18 | 176 |
| Long Grove | Grayslake, Mundelein, Round Lake, Wauconda | Mundelein 4 Wsw | Apr 29 | Oct 20 | 172 |
| Marseilles | Seneca, Sheridan, Wedron, Grand Ridge, Serena | Marseilles Lock | Apr 27 | Oct 17 | 171 |
| Mendota | Earlville, Paw Paw, Leland, Sublette, Lee, Compton, +1 more | Paw Paw 2s | Apr 27 | Oct 15 | 171 |
| Milford | — | Hoopeston | Apr 22 | Oct 19 | 180 |
| Minonk | El Paso, Toluca, Roanoke, Wenona, Rutland, Flanagan, +6 more | Minonk | Apr 26 | Oct 17 | 173 |
| Monmouth | Media, Kirkwood, Roseville, Alexis, Little York | Monmouth | Apr 22 | Oct 15 | 174 |
| Morris | Minooka, Coal, Braidwood, Newark, Millington, Mazon | Morris 1 Nw | Apr 20 | Oct 23 | 184 |
| Morrison | Erie, Prophetstown, Lyndon, Galt | Morrison | Apr 26 | Oct 13 | 167 |
| Naperville | Wheaton, Lisle, Glen Ellyn, Darien, Warrenville, Glendale Heights | Wheaton 3 Se | Apr 27 | Oct 17 | 173 |
| Oquawka | Mediapolis, Biggsville | Gladstone Dam 18 | Apr 8 | Oct 29 | 202 |
| Oregon | Mount Morris, Polo, Forreston, Leaf River | Polo 5nw | Apr 29 | Oct 7 | 161 |
| Ottawa | Streator, Leonore | Ottawa 5sw | Apr 20 | Oct 22 | 183 |
| Palatine | — | Chicago Palwaukee Ap | Apr 19 | Oct 26 | 190 |
| Pecatonica | German Valley, Ridott | Freeport Waste Wtp | Apr 26 | Oct 13 | 169 |
| Peoria | Trivoli, Farmington, Elmwood, Brimfield, Cuba, Norwood, +1 more | Peoria Gtr Peoria Ap | Apr 16 | Oct 23 | 189 |
| Plainfield | — | Romeoville Wfo | Apr 20 | Oct 22 | 184 |
| Princeton | De Pue, La Moille, Wyanet, Tiskilwa, Arlington, Dover | Princeton | Apr 22 | Oct 17 | 177 |
| Ransom | Cornell, Flanagan, Saunemin | Pontiac | Apr 16 | Oct 24 | 191 |
| Rock Island | Moline, Coal Valley, Ophiem, Preemption, Edgington, Orion, +3 more | Moline Quad City Intl Ap | Apr 24 | Oct 18 | 176 |
| Rockford | Loves Park, Machesney Park, Cherry Valley, Byron, Davis Junction, New Milford, +5 more | Rockford Gtr Rockford Ap | Apr 24 | Oct 17 | 174 |
| Roselle | — | Chicago Ohare Intl Ap | Apr 16 | Oct 28 | 193 |
| Sciota | Good Hope, Raritan | La Harpe | Apr 21 | Oct 19 | 180 |
| Shabbona | — | Shabbona 5 Nne | Apr 28 | Oct 10 | 163 |
| Watseka | Gilman, Onarga, Ashkum, Sheldon, Iroquois, Woodland, +6 more | Watseka 2 Nw | Apr 24 | Oct 16 | 174 |
| Yates | Gilson, Maquon | Knoxville | Apr 21 | Oct 20 | 181 |
| Yorkville | Sugar Grove, Plano, Sandwich, Big Rock, Elburn, Somonauk, +3 more | Chicago Aurora Muni Ap | Apr 28 | Oct 13 | 166 |
* LaSalle 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 (LaSalle, representative)
Computed from LaSalle's average frost dates — the median-season location in this Illinoiszone 5b 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 27 – Mar 13 | May 1 – May 8 | Jun 30 – Jul 20 | — | matures comfortably |
| Pepper | Very tender | Feb 13 – Feb 27 | May 8 – May 15 | Jul 7 – Aug 6 | — | matures comfortably |
| Cucumber | Tender | Mar 27 – Apr 3 | May 1 – May 8 | Jun 20 – Jul 10 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 1 – May 8 | Jun 15 – Jun 30 | — | matures comfortably |
| Bush bean | Tender | — | May 1 – May 8 | Jun 20 – Jun 30 | Aug 19 – Aug 29 | matures comfortably |
| Sweet corn | Tender | — | Apr 24 – May 8 | Jun 23 – Jul 23 | — | matures comfortably |
| Basil | Very tender | Mar 13 – Mar 27 | May 1 – May 8 | May 31 – Jun 15 | — | matures comfortably |
| Lettuce | Half-hardy | Mar 13 – Mar 27 | Mar 27 – Apr 10 | May 11 – May 26 | Aug 5 – Aug 20 | matures comfortably |
| Pea | Hardy | — | Mar 13 – Mar 27 | May 7 – May 22 | Jul 26 – Aug 10 | matures comfortably |
| Spinach | Hardy | — | Mar 13 – Mar 27 | Apr 22 – May 2 | Aug 15 – Aug 25 | matures comfortably |
| Carrot | Half-hardy | — | Apr 3 – Apr 10 | Jun 2 – Jun 22 | Jul 16 – Aug 5 | matures comfortably |
| Broccoli | Half-hardy | Feb 27 – Mar 13 | Mar 27 – Apr 10 | May 21 – Jun 10 | Jul 21 – Aug 10 | matures comfortably |
Which crops fit this growing season
Using LaSalle's own 176-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 (LaSalle)
From NOAA's 1991–2020 Climate Normals at station USC00116753. 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 | May 4 | May 19 | Oct 6 | Oct 20 | 155 |
| 32°F (freeze) | Apr 24 | May 8 | Oct 18 | Oct 28 | 176 |
| 28°F | Apr 13 | Apr 27 | Oct 28 | Nov 8 | 197 |
| 24°F | Apr 2 | Apr 17 | Nov 7 | Nov 21 | 220 |
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 57 locations is 3,204; LaSalle's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 3,121 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 5,262 | cool-season crops (brassicas, greens) |
Hardiness zone 5b in Illinois
Zone 5b means an average annual extreme minimum winter temperature of about −15 to −10 °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, 6a, 6b, 7a.
Explore zone 5b in other states at zone 5b, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 5b mean in Illinois?
- Zone 5b means an average annual extreme minimum winter temperature of −15 to −10 °F — the standard USDA measure of which perennials survive winter. 57 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 5b is the growing season longest?
- Oquawka runs the longest season on this page at about 202 days; Oregon is shortest at about 161 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 5b?
- Using LaSalle's frost dates (this page's median-season location): start seeds indoors about Feb 27 – Mar 13, then transplant outside about May 1 – May 8. 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 5b 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 57 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.