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State guide

Planting zones in Illinois

Illinois spans USDA zones 5a to 7a across its 1,382 ZIP codes, so there is no single zone for the state and anyone who gives you one is rounding. 40% of its ZIP codes are zone 6a; the rest are not.

USDA zones 5a–7a 5 zones across the state
ZIP codes 1,382 1,382 have a NOAA station within range
Weather stations 170 In Illinois, NOAA 1991–2020 normals

Your ZIP code

Get the exact answer for your address

Everything above describes Illinois as a whole. Hardiness zones and freeze dates are published per ZIP code, so yours is exact — enter it and this page will tell you your zone, which NOAA station it comes from and how far away that station is.

Works for all 40,502 US ZIP codes. Freeze dates need a NOAA station within 100 km; where there is none, the page says so rather than estimating one.

Which zone you are in depends where you are

Illinois covers 5 hardiness zones. A guide that gives the state one zone has picked whichever is largest and rounded everyone else into it — which is fine for the 40% in zone 6a and wrong for the other 60%. Here is the actual split, by ZIP code.

Zone ZIP codes Share  
6a 558 40%
5b 407 29%
6b 232 17%
7a 157 11%
5a 28 2%

Zones are published per ZIP code, so yours is exact even though the state's is not. The hardiness tool will tell you which one you are in.

Your freeze dates

Last spring freeze April 2 – May 2
First fall freeze October 7 – November 5

Those are the earliest and latest medians among the 170 stations in Illinois with an ordinary freeze window — not an average, and not one station standing in for the rest. Half of years freeze later than a station's own median.

Your growing season

NOAA publishes a growing-season length for each station, and across the 170 stations in Illinois it runs 154–216 days . That figure is published, not computed from the two freeze dates — subtracting one from the other gives the wrong answer wherever a season crosses New Year. Mean summer high (June–August) runs 79–89 °F , below the 90 °F point where cool-season crops reliably bolt.

The ends of each range, named

A range with no station behind it cannot be checked, and Illinois has too many stations to table them all. So every figure above is reported here with the station standing at each end of it, by name and NOAA ID. No station on this page represents Illinois — these are its edges, which is a different claim.

Measure Earliest / lowest Station Latest / highest Station
Last spring freeze April 2 Mt Carmel, IL USC00115888 May 2 Mt Carroll, IL USC00115901
First fall freeze October 7 Mt Carroll, IL USC00115901 November 5 Grand Chain Dam 53, IL USC00113580
Growing season 154 days Mt Carroll, IL USC00115901 216 days Grand Chain Dam 53, IL USC00113580
Mean summer high 79 °F Chicago Northerly Is, IL USC00111550 89 °F Belleville Siu Rsch, IL USW00013802

These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.

When to start seeds in Illinois

Every spring job for 63 crop dates, counted from this state's own last spring freeze. Each is a range across all 170 stations — the earliest and latest that job falls anywhere in Illinois — because no one station speaks for a whole state. The ranges are wide on purpose: that width is the state.

Crop Job When Offset
Green Onions Start indoors February 5 – March 7 8 weeks before
Peppers Start indoors February 5 – March 7 8 weeks before
Broccoli Start indoors February 19 – March 21 6 weeks before
Cabbage Start indoors February 19 – March 21 6 weeks before
Collards Start indoors February 19 – March 21 6 weeks before
Kale Start indoors February 19 – March 21 6 weeks before
Leaf Lettuce Start indoors February 19 – March 21 6 weeks before
Peas Direct sow February 19 – March 21 6 weeks before
Spinach Direct sow February 19 – March 21 6 weeks before
Sweet Potato Start indoors February 19 – March 21 6 weeks before
Tomatoes Start indoors February 19 – March 21 6 weeks before
Bok Choy Start indoors February 26 – March 28 5 weeks before
Kohlrabi Start indoors February 26 – March 28 5 weeks before
Swiss Chard Start indoors February 26 – March 28 5 weeks before
Arugula Direct sow March 5 – April 4 4 weeks before
Baby Salad Greens Direct sow March 5 – April 4 4 weeks before
Beets Direct sow March 5 – April 4 4 weeks before
Green Onions Direct sow March 5 – April 4 4 weeks before
Mustard Greens Direct sow March 5 – April 4 4 weeks before
Okra Start indoors March 5 – April 4 4 weeks before
Radishes Direct sow March 5 – April 4 4 weeks before
Turnips Direct sow March 5 – April 4 4 weeks before
Cabbage Set out March 12 – April 11 3 weeks before
Carrots Direct sow March 12 – April 11 3 weeks before
Collards Direct sow March 12 – April 11 3 weeks before
Collards Set out March 12 – April 11 3 weeks before
Cucumbers Start indoors March 12 – April 11 3 weeks before
Green Onions Set out March 12 – April 11 3 weeks before
Kale Direct sow March 12 – April 11 3 weeks before
Kale Set out March 12 – April 11 3 weeks before
Kohlrabi Direct sow March 12 – April 11 3 weeks before
Kohlrabi Set out March 12 – April 11 3 weeks before
Leaf Lettuce Direct sow March 12 – April 11 3 weeks before
Pumpkins Start indoors March 12 – April 11 3 weeks before
Summer Squash Start indoors March 12 – April 11 3 weeks before
Winter Squash Start indoors March 12 – April 11 3 weeks before
Zucchini Start indoors March 12 – April 11 3 weeks before
Bok Choy Direct sow March 19 – April 18 2 weeks before
Bok Choy Set out March 19 – April 18 2 weeks before
Broccoli Set out March 19 – April 18 2 weeks before
Cilantro Direct sow March 19 – April 18 2 weeks before
Leaf Lettuce Set out March 19 – April 18 2 weeks before
Swiss Chard Direct sow March 19 – April 18 2 weeks before
Swiss Chard Set out March 19 – April 18 2 weeks before
Dill Direct sow March 26 – April 25 1 week before
Bush Beans Direct sow April 9 – May 9 1 week after
Cucumbers Set out April 9 – May 9 1 week after
Pumpkins Direct sow April 9 – May 9 1 week after
Pumpkins Set out April 9 – May 9 1 week after
Summer Squash Direct sow April 9 – May 9 1 week after
Summer Squash Set out April 9 – May 9 1 week after
Sweet Corn Direct sow April 9 – May 9 1 week after
Tomatoes Set out April 9 – May 9 1 week after
Winter Squash Direct sow April 9 – May 9 1 week after
Winter Squash Set out April 9 – May 9 1 week after
Zucchini Direct sow April 9 – May 9 1 week after
Zucchini Set out April 9 – May 9 1 week after
Cucumbers Direct sow April 16 – May 16 2 weeks after
Okra Direct sow April 16 – May 16 2 weeks after
Okra Set out April 16 – May 16 2 weeks after
Peppers Set out April 16 – May 16 2 weeks after
Southern Peas Direct sow April 16 – May 16 2 weeks after
Sweet Potato Set out April 16 – May 16 2 weeks after

The week offsets are conventional extension guidance and vary by variety; the freeze dates they are counted from are measured. For a single date rather than a range, run when do I start my seeds? with your own ZIP code.

What survives the winter changes across Illinois

Of 74 perennial fruits, nuts, berries, vegetables and herbs, 58 come through the winter in zone 7a and only 48 in zone 5a. Winter hardiness runs on the zone alone, so each row below is exact for the ZIP codes in it.

Zone ZIPs Survive Fail for being too warm
5a 28 48 of 74 0
5b 407 48 of 74 0
6a 558 51 of 74 0
6b 232 51 of 74 0
7a 157 58 of 74 1

The last column is the counterintuitive one. Most temperate fruit needs a documented number of hours below about 45 °F to break dormancy and set a crop, so an apple fails in a winter that is too warm; currants and rhubarb cook in the summer heat that comes with it. See the full list with reasons.

Your own ZIP

Work out your own dates

Each of these takes a ZIP code and answers for that ZIP alone, citing the station it used and how far away it is. There is a ZIP box in the header of every page.

Metro areas in Illinois

12 metro areas here have its own page, with the freeze dates from every station serving it, a spring calendar built from those stations, and every ZIP code in it listed with that ZIP code's exact zone and nearest station.

Counties in Illinois

30 countys here have its own page, listing every ZIP code in it with that ZIP code's exact zone and nearest station. These are the smaller places outside the metro areas above — where most of Illinois's ZIP codes actually are.

Other states to compare

All 52 states · All 388 metro areas · All county pages

Gear

If you want to act on this

Each link opens an Amazon search rather than a product we picked. We have not tested these and do not rank them — the search is the honest version, and you choose.

As an Amazon Associate we earn from qualifying purchases. That costs you nothing extra, and it buys no influence over anything on this site: the dates come from NOAA normals and the zones from the USDA, and no product affects either.

Sources

Where these numbers come from

The hardiness zone is the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. The freeze dates, growing seasons and summer highs are NOAA's 1991–2020 Climate Normals, read from every station in Illinois. Which ZIP codes are in Illinois comes from the Census ZIP-to-county relation, since a county's federal code begins with its state's. Nothing here is estimated.

This page names no single station for Illinois on purpose. Picking one to represent a state sounds reasonable and is not — the same reason the metro pages refuse it, only more so at this size. Instead every range names the station at each end, so you can check both without either one being made to speak for the state.

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