When to Plant Cucumbers in Illinois: Spring and Fall Dates by Region
Planting dates for cucumbers from University of Illinois Extension in Illinois, with 50% frost dates from NOAA for Chicago O'Hare International Airport, Peoria Greater Peoria Airport, and Springfield Capital Airport and one worked case.
Updated
Figures checked against their sources on ; next check .
For cucumbers, University of Illinois Extension prints 3 regions under the heading “Cucumber from Seed”; the table below copies each entry as printed. How far apart are the rows? 27 days, from April 27 in Southern Illinois to May 24 in Northern Illinois.
The cucumber windows by region
The page adds this line for the row: “Sow 12" apart, 1" deep.”
| Region | First planting | Second planting |
|---|---|---|
| Northern Illinois | May 24 to June 30 | — |
| Central Illinois | May 10 to June 15 | — |
| Southern Illinois | April 27 to June 1 | — |
What to know about this source
Growing season length, it adds, runs from 215 days in far southern Illinois to 180 days in far northern Illinois. Where a crop lists two ranges, the page says it can be planted and harvested twice, for a summer and a fall crop.
Starting cucumbers indoors
If you raise your own transplants, count backward from the set-out date. UNH’s fact sheet allows 3 to 4 weeks for that stage, and the table lists what the others say.
Of the saved sources, one gives weeks for cucumbers (UNH) and one gives a handling tip (Minnesota).
In the garden itself, UNH sows cucumbers once the soil reaches 70 °F, which a soil thermometer answers better than any calendar.
| Source | What it says |
|---|---|
| University of New Hampshire | 3 to 4 weeks from seed to transplant; 1 to 2 weeks after the last frost is safe to set out |
| University of Minnesota | Cucumbers and squash transplant poorly, so raise them in fiber or paper pots that break down in the soil |
Where the frost dates fall in Illinois
NOAA’s 1991-2020 normals give nine probability levels for each station; the table keeps only the middle one, the even-odds date, and the links open the rest.
The last column maps a station to a region only where University of Illinois Extension or its county list settles it.
| Station | Last spring 32°F | First fall 32°F | Region in Illinois’s calendar |
|---|---|---|---|
| Chicago O'Hare International Airport, Illinois | April 16 | October 28 | Northern Illinois |
| Peoria Greater Peoria Airport, Illinois | April 16 | October 23 | Not stated by the source |
| Springfield Capital Airport, Illinois | April 14 | October 20 | Not stated by the source |
| Carbondale Southern Il Airport, Illinois | April 9 | October 22 | Not stated by the source |
| Rockford Greater Rockford Airport, Illinois | April 24 | October 17 | Not stated by the source |
Worked example
For a gardener near Chicago O'Hare International Airport, NOAA’s even-odds frost dates are April 16 in spring and October 28 in fall.
Here the window starts May 24 (38 days after the median last freeze) and ends June 30 (75 days after it), under the Northern Illinois heading.
Treat the result as a way to see how far the printed dates sit from a real frost record. Your yard may run weeks off the station, so repeat the sum with the station closest to you.
Before you rely on these dates
The page tells readers to always confirm dates with the seed packet or plant tag.
Treat the table as a starting range and look at the ten-day forecast before setting out anything tender.
Sources (4)
- University of Illinois Extension (Kelly Allsup), When to Plant, Home Vegetable Gardening, updated August 2025 extension.illinois.edu
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991-2020, annual and seasonal normals (frost/freeze probabilities by station) ncei.noaa.gov
- University of New Hampshire Cooperative Extension, Growing Vegetables: When to Plant Your Vegetable Garden (fact sheet) extension.unh.edu
- University of Minnesota Extension, Starting seeds indoors (page reviewed 2026) extension.umn.edu