Seed Starting Calendar for Illinois

Q: When is the last frost in Illinois?

It depends on the station. The earliest median last spring freeze in Illinois is April 2 at Mount Carmel; the latest is May 2 at Mount Carroll. A median is a coin flip: at Chicago the last 32°F freeze comes after April 10 in half of years, and has passed by April 25 in 9 of 10 years (NOAA 1991 to 2020 normals).

Q: When can I plant tomatoes outside in Illinois?

UNH Extension sets tomatoes out 1 to 2 weeks after the last frost, which at Chicago is Apr 17 to Apr 24 in 2027. Tomatoes are frost tender, so the date to watch is April 25, when 9 of 10 springs at Chicago have had their last 32°F night. Hardening off starts two weeks before setting out (Apr 3 to Apr 17).

Q: What months do I plant vegetables in Illinois?

University of Illinois Extension publishes planting months by region (Northern Illinois, Central Illinois, Southern Illinois). For Northern Illinois, tomatoes go in during May and June. Seeds for transplants go in 4 to 10 weeks ahead of those months, depending on the crop.

Q: What does University of Illinois Extension say about planting dates in Illinois?

University of Illinois Extension's When to Plant (Illinois Fruit and Vegetable Planting Dates) puts it this way: "The following chart covers suggested date ranges to plant vegetable seeds or transplants outside in northern, central, and southern Illinois." The guide is linked below with the date it was read (September 21, 2026).

Q: How many weeks before the last frost do I start peppers and eggplant?

UNH Extension gives 8 to 10 weeks from seed to transplant for both, and sets peppers out 2 weeks after the last frost and eggplant 2 to 3 weeks after, so the sowing date is 6 to 8 weeks before the median last frost. At Chicago that is Feb 13 to Feb 27 for peppers.

Q: How long do seedlings need to harden off?

About two weeks. University of Missouri Extension: "Hardening should be started about two weeks before planting in the garden." University of Minnesota Extension adds that seedlings should go out on a cloudy day or in the late afternoon.

Median last frost from Apr 4 to Apr 28 across Illinois

NOAA stations

168

Median last frost, Chicago

Apr 10

Passed in 9 of 10 years

Apr 25

Last frost

Last spring frost dates in Illinois

Carbondale in southern Illinois and Chicago on the lakefront share a median last frost around Apr 9 to Apr 10, while Moline in the Quad Cities waits until about Apr 24.

Three dates per station from the NOAA 1991 to 2020 normals. The median is the date half of springs run past. The last column is the date the last 32°F night has passed by in 9 years out of 10, the one to hold tender transplants for.

Station	Elevation	Early (1 in 10 years later than this)	Median last frost	Passed in 9 of 10 years	Median first fall frost
Lawrenceville Intl AirportLawrenceville Intl Airport, USW00013809	429 ft	Mar 26	Apr 8	Apr 22	Oct 26
CarbondaleCarbondale Southern Il Airport, USW00093810	406 ft	Mar 24	Apr 9	Apr 25	Oct 22
ChicagoChicago Northerly Is, USC00111550	583 ft	Mar 29	Apr 10	Apr 25	Nov 5
SpringfieldSpringfield Capital Airport, USW00093822	594 ft	Apr 1	Apr 14	Apr 29	Oct 20
Moline Quad City Intl AirportMoline Quad City Intl Airport, USW00014923	592 ft	Apr 9	Apr 24	May 9	Oct 18

Crop chart

When to start seeds in Illinois, spring 2027

Counted back from the median last frost at Chicago, April 10. Pick another station to redraw the chart for it.

Start indoorsHarden offSet outSow outdoorsMedian last frostLast freeze passed in 9 of 10 years

Every crop, counted from a median last frost of April 10
Crop	Start indoors	Set out	Sow outdoors	Frost class
Tomato	Feb 20 to Mar 6	Apr 17 to Apr 24		Tender, very tender
Pepper	Feb 13 to Feb 27	Apr 24 to May 1		Tender, very tender
Eggplant	Feb 13 to Feb 27	Apr 24 to May 1		Tender, very tender
Basil	Feb 27 to Mar 13	Apr 24 to May 1		Tender
Celery	Jan 16 to Jan 30	Apr 10 to Apr 17		Tender
Cucumber	Mar 20 to Mar 27	Apr 17 to Apr 24	Apr 10 to Apr 17	Tender
Summer squash	Mar 27 to Apr 3	Apr 24 to May 1	Apr 10 to Apr 17	Tender
Winter squash	Mar 27 to Apr 3	Apr 24 to May 1	Apr 24 to May 1	Tender, very tender
Pumpkin	Mar 27 to Apr 3	Apr 24 to May 1	Apr 24 to May 1	Tender, very tender
Melon (cantaloupe)	Mar 27 to Apr 3	Apr 24 to May 1		Tender, very tender
Watermelon	Mar 20 to Apr 3	Apr 24 to May 1		Tender, very tender
Onion (from seed)	Jan 2 to Jan 16	Mar 13 to Mar 20		Hardy
Leek	Jan 2 to Jan 16	Mar 13 to Mar 20		Hardy
Parsley	Jan 9 to Jan 16	Mar 20 to Mar 27		Half-hardy
Broccoli	Jan 30 to Feb 13	Mar 13 to Mar 27		Hardy
Brussels sprouts	Jan 30 to Feb 13	Mar 13 to Mar 27		Hardy
Cabbage	Jan 30 to Feb 13	Mar 13 to Mar 20		Hardy
Cauliflower	Feb 13 to Feb 27	Mar 27 to Apr 3		Half-hardy
Kale	Jan 30 to Feb 13	Mar 13 to Mar 20		Hardy
Lettuce	Feb 6 to Feb 13	Mar 13 to Mar 20		Hardy
Swiss chard	Feb 13 to Feb 27	Mar 27 to Apr 3	Mar 13 to Mar 20	Half-hardy
Spinach	Jan 16 to Jan 30	Feb 27 to Mar 20	Mar 13 to Mar 27	Hardy
Peas			Mar 13 to Mar 27	Hardy
Radish			Mar 13 to Mar 27	Hardy
Carrot			Mar 27 to Apr 10	Half-hardy
Beet			Mar 27 to Apr 10	Half-hardy
Beans			Apr 10 to Apr 17	Tender
Sweet corn			Apr 10 to Apr 17	Tender

Six square pots of dark compost seen from above, each holding a single seedling with two narrow seed leaves — Tomato seedlings at the seed leaf stage, one to a pot. The University of Minnesota Extension holds off on fertilizer until a seedling has several sets of true leaves, then feeds at quarter strength once a week. “Tomato Seedlings (49768696597)” by Amanda Slater from Coventry, West Midlands, UK, CC BY-SA 2.0

Extension guide

What University of Illinois Extension advises

University of Illinois Extension publishes the planting guide Illinois gardeners work from, When to Plant (Illinois Fruit and Vegetable Planting Dates).

“The following chart covers suggested date ranges to plant vegetable seeds or transplants outside in northern, central, and southern Illinois.”

University of Illinois Extension, When to Plant (Illinois Fruit and Vegetable Planting Dates), quoted exactly.

“It will tell you when the seeds should be sown or planted. Example: X numbers of weeks before the last frost.”

University of Illinois Extension, Starting a Garden: Seed Starting (Good Growing blog), quoted exactly.

“Warm season plants that are considered very tender are the plants that most people associate with vegetable gardens, such as cucumber, pepper, pumpkin, squash, tomatoes, and watermelons.”

University of Illinois Extension, on cucumber, quoted exactly.

Planting months

University of Illinois Extension planting months for Illinois

The extension also publishes planting months by region. Each filled cell is a month the guide gives for planting that crop.

Northern Illinois (median last 32F freeze April 8 to 29)

Crop	Apr	May	Jun	Jul	Aug	Sep
beans		May	Jun	Jul	Aug
beets	Apr	May	Jun	Jul
broccoli	Apr	May		Jul
cabbage	Apr	May	Jun	Jul
carrot	Apr	May	Jun	Jul
cauliflower				Jul	Aug
sweet corn		May	Jun	Jul
cucumber		May	Jun
eggplant		May	Jun
kale	Apr	May			Aug
lettuce	Apr	May		Jul	Aug	Sep
melon			Jun
onion	Apr	May
peas	Apr	May
pepper			Jun	Jul
pumpkin			Jun
radish	Apr	May	Jun		Aug	Sep
spinach	Apr				Aug	Sep
summer squash		May	Jun
winter squash			Jun
tomato		May	Jun
watermelon		May	Jun	Jul

Planting months from University of Illinois Extension, When to Plant (Illinois Fruit and Vegetable Planting Dates), read 2026-09-21. Tomatoes in Northern Illinois: May and June.

A gardener kneeling beside a raised bed setting a young tomato plant into dark soil, an empty nursery pot beside her — Setting out a tomato in June at a community garden. Tender crops go out after the last frost, and after a week or two of hardening off outdoors. “Volunteer planting heirloom tomato (4704185147)”, Pacific Southwest Region 5, Public domain

Seed starting questions for Illinois

When should I start seeds indoors in Illinois?

Count back from the median last frost where you garden. At Chicago (Chicago Northerly Is) that date is April 10, so for spring 2027 onions start indoors Jan 2 to Jan 16, peppers Feb 13 to Feb 27 and tomatoes Feb 20 to Mar 6. Across Illinois's 168 NOAA stations the median last frost runs from Apr 4 to Apr 28 for the middle 90 percent, so a garden near Mount Carroll starts later than one near Mount Carmel.

When is the last frost in Illinois?

When can I plant tomatoes outside in Illinois?

What months do I plant vegetables in Illinois?

What does University of Illinois Extension say about planting dates in Illinois?

How many weeks before the last frost do I start peppers and eggplant?

How long do seedlings need to harden off?

Why do seed starting dates differ across Illinois?

Frost dates from NOAA NCEI U.S. Climate Normals 1991-2020, annual/seasonal, by station (v1.0.1). Planting guidance from University of Illinois Extension, quoted exactly. Seed starting weeks from UNH Cooperative Extension. Compiled 2026-09-21.

First frost in IllinoisThe other end of the season: when fall frost ends the tender crops.Soil temperatureBeans, corn and squash sown direct wait on warm soil as well as the last frost.Illinois lawn care calendarSpring seeding, feeding and mowing dates on the same climate.Fall planting calendarGarlic, cool season crops and a second sowing window in the fall.Frost dates by ZIPFirst and last frost odds for any address.