When to Plant Tomatoes in Illinois: Spring and Fall Dates by Region
University of Illinois Extension’s own tomatoes dates for Illinois, row by row and never averaged, beside NOAA frost dates for Chicago O'Hare International Airport, Peoria Greater Peoria Airport, and Springfield Capital Airport.
Updated
Figures checked against their sources on ; next check .
Open University of Illinois Extension’s calendar to the tomato line under the heading “Tomato from Transplant” and you find 3 regions, each with its own spring and fall entries. Northern Illinois starts latest, on May 24, while Southern Illinois starts on April 28: 26 days between the two.
Illinois’s dates, row by row
The page adds this line for the row: “Sow 24-36" apart. Bury the transplant up to the bottom two leaves.”
| Region | First planting | Second planting |
|---|---|---|
| Northern Illinois | May 24 to June 15 | — |
| Central Illinois | May 10 to June 1 | — |
| Southern Illinois | April 28 to May 15 | — |
How the Illinois calendar is built
Southern gardeners can generally start two weeks earlier than central Illinois and harvest for about two weeks longer; northern Illinois can plant about two weeks later than central, the page says. Growing season length, it adds, runs from 215 days in far southern Illinois to 180 days in far northern Illinois.
Starting tomatoes indoors
How early to sow indoors depends on the crop more than the state, and the saved sources agree on the shape if not the numbers; UNH’s figure is 6 to 8 weeks.
For tomatoes the saved record holds six sources. Three of them (UNH, NDSU and Montana State) count from the last frost; the University of Minnesota, NC State and the University of Georgia describe their own climates. The shortest figure is 5 weeks and the longest 10, so no single number is right for every garden.
Once the seedlings are ready, UNH says tomatoes are safe to set out 1 to 2 weeks after the last frost, after hardening off.
| Source | What it says |
|---|---|
| University of New Hampshire | 6 to 8 weeks from seed to transplant; 1 to 2 weeks after the last frost is safe to set out |
| North Dakota State University | Sow 6 weeks before the last frost, transplant 2 weeks after it |
| Montana State University | 6 to 10 weeks to transplant size; the planting window opens 1 week before the last frost |
| University of Minnesota | Early April in Minnesota, 5 to 6 weeks indoors |
| NC State | Any transplant: seed 6 to 8 weeks before setting out (central North Carolina calendar) |
| University of Georgia | 6 weeks from seed to transplant size (middle Georgia calendar) |
Typical frost dates at Illinois stations
The 50% date is the even-odds one: in half of the years the last spring 32°F night comes on or after it, and the first fall one on or before it. Each station below links to the frost dates tool.
A station is tied to a region of the calendar only where the source’s own wording makes that call; the rest are left blank on purpose.
| 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
Start from Chicago O'Hare International Airport: the station’s median last spring freeze is April 16, and its median first fall freeze is October 28.
Set the frost date against Northern Illinois: the window opens May 24, 38 days after it, and shuts June 15, 60 days after it.
The offsets will shift by a few days with every revision of the normals, so use them as a rough guide to which row to trust and not as a deadline.
Before you rely on these dates
The page tells readers to always confirm dates with the seed packet or plant tag.
A late cold snap after a mild March is the usual way these windows go wrong; keep a sheet or row cover on hand.
Sources (8)
- 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
- NDSU Extension Service (North Dakota State University), Time and Temperature Chart, from How to Succeed at Seed Starting, publication h1139, print code 2M-2-99 library.nd.gov
- Montana State University Extension (Amy Grandpre), Can I Grow That Here? Vegetable Seed and Transplant Schedules for Garden or Container, MontGuide MT199308AG, revised November 2018 extension-store.montana.edu
- University of Minnesota Extension, Starting seeds indoors (page reviewed 2026) extension.umn.edu
- NC State Extension (Bradley, Gunter, Sherk and Driscoll), Central North Carolina Planting Calendar for Annual Vegetables, Fruits, and Herbs, AG-756-01, published July 8, 2016 content.ces.ncsu.edu
- University of Georgia Cooperative Extension (Bob Westerfield), Vegetable Garden Calendar, Circular 943, published with full review March 10, 2026 extension.uga.edu