What USDA hardiness zone is Knox County, Illinois?

Every ZIP code in Knox County, Illinois is USDA hardiness zone 5b, from the USDA 2023 Plant Hardiness Zone Map.

When is the last spring frost in Knox County, Illinois?

The median last spring freeze runs April 20 – April 28 across the 4 NOAA weather stations serving Knox County, Illinois, from NOAA 1991-2020 Climate Normals. Half of years freeze later than the median.

Illinois

Planting zones in Knox County, Illinois

Every ZIP code in this county is USDA zone 5b — so unlike most of the places people look up, there is one right answer here and it holds wherever you are in the county.

USDA zone 5b The same in all 17 ZIP codes

ZIP codes 17 17 have a NOAA station within range

Weather stations 4 NOAA 1991–2020 normals, across 716 sq mi

Your ZIP code

Get the exact answer for your address

Everything above describes Knox County, 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.

The growing season in Knox County is closing

Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives October 12 – October 20 across the 4 NOAA stations serving this county .

Your next season already has a date

The first job of it is 🧅 Green Onions, start indoors, around February 23 – March 3 — counted back from a last spring freeze of April 20 – April 28 here.

Every spring date for your ZIP →

These are ranges across the whole county. The ZIP lookup above gives the dates from your own nearest station instead.

All 4 stations agreeAt least one station

Every one of the 4 NOAA stations serving this county counts April 28 – October 12 as growing season (167 days). Widening to any single station gives April 20 – October 20 (183 days).

Your freeze dates

Last spring freeze April 20 – April 28

First fall freeze October 12 – October 20

Across the 4 NOAA stations serving this county. These are medians — half of years freeze later than the date shown — so treat the later end of each range as the cautious one.

The growing season runs 165–181 days depending which station you are nearest, as published by NOAA rather than computed from the dates above. Summer highs average 81.9–82.5 °F in June–August. Summer rain over the same months runs 12.3–12.5" across those 4 stations, against the rough inch a week — about 13 inches over the same 92 days — that a vegetable garden is usually reckoned to want. The middle station covers about 95% of it, so expect to make up the rest. The inches are NOAA's published normals; the inch a week is a rule of thumb, and it takes no account of a 82 °F summer afternoon drying the soil faster than a cool one.

Every ZIP code in Knox County

Zones are published per ZIP code, not per county, so this is the exact answer rather than the county's average. The station column is the nearest one to that ZIP code's centroid and how far away it is — the same figure the tools use, shown here so you can see which ZIP codes are well covered and which are reaching.

ZIP code	USDA zone	Nearest NOAA station	Distance
61401	5b	Galesburg, IL	0.2 km
61402	5b	Galesburg, IL	1.9 km
61410	5b	Avon, IL	14.8 km
61414	5b	Altona, IL	1.0 km
61428	5b	Knoxville, IL	15.2 km
61430	5b	Knoxville, IL	5.0 km
61436	5b	Knoxville, IL	7.3 km
61439	5b	Galesburg, IL	9.7 km
61448	5b	Knoxville, IL	5.2 km
61458	5b	Knoxville, IL	16.1 km
61467	5b	Altona, IL	8.7 km
61472	5b	Galesburg, IL	17.4 km
61474	5b	Avon, IL	9.7 km
61485	5b	Altona, IL	13.4 km
61488	5b	Galesburg, IL	10.8 km
61489	5b	Knoxville, IL	21.8 km
61572	5b	Knoxville, IL	24.1 km

ZIP-code positions are area centroids, so a large rural ZIP code's listed distance is measured from the middle of its area rather than from any particular address in it.

When to start seeds in Knox County

Every date below is anchored on the last spring freeze at each station and reported as a range across all 4 of them, because no one station speaks for the county.

Crop	Job	When	Offset
🧅 Green Onions	Start indoors	February 23 – March 3	8 wk before
🌶️ Peppers	Start indoors	February 23 – March 3	8 wk before
🥦 Broccoli	Start indoors	March 9 – March 17	6 wk before
🥬 Cabbage	Start indoors	March 9 – March 17	6 wk before
🥬 Collards	Start indoors	March 9 – March 17	6 wk before
🥬 Kale	Start indoors	March 9 – March 17	6 wk before
🥬 Leaf Lettuce	Start indoors	March 9 – March 17	6 wk before
🫛 Peas	Direct sow	March 9 – March 17	6 wk before
🥬 Spinach	Direct sow	March 9 – March 17	6 wk before
🍠 Sweet Potato	Start indoors	March 9 – March 17	6 wk before
🍅 Tomatoes	Start indoors	March 9 – March 17	6 wk before
🥬 Bok Choy	Start indoors	March 16 – March 24	5 wk before
🥬 Kohlrabi	Start indoors	March 16 – March 24	5 wk before
🥬 Swiss Chard	Start indoors	March 16 – March 24	5 wk before
🥬 Arugula	Direct sow	March 23 – March 31	4 wk before
🥬 Baby Salad Greens	Direct sow	March 23 – March 31	4 wk before
🥕 Beets	Direct sow	March 23 – March 31	4 wk before
🧅 Green Onions	Direct sow	March 23 – March 31	4 wk before
🥬 Mustard Greens	Direct sow	March 23 – March 31	4 wk before
🌶️ Okra	Start indoors	March 23 – March 31	4 wk before
🌱 Radishes	Direct sow	March 23 – March 31	4 wk before
🥔 Turnips	Direct sow	March 23 – March 31	4 wk before
🥬 Cabbage	Set out	March 30 – April 7	3 wk before
🥕 Carrots	Direct sow	March 30 – April 7	3 wk before
🥬 Collards	Direct sow	March 30 – April 7	3 wk before
🥬 Collards	Set out	March 30 – April 7	3 wk before
🥒 Cucumbers	Start indoors	March 30 – April 7	3 wk before
🧅 Green Onions	Set out	March 30 – April 7	3 wk before
🥬 Kale	Direct sow	March 30 – April 7	3 wk before
🥬 Kale	Set out	March 30 – April 7	3 wk before
🥬 Kohlrabi	Direct sow	March 30 – April 7	3 wk before
🥬 Kohlrabi	Set out	March 30 – April 7	3 wk before
🥬 Leaf Lettuce	Direct sow	March 30 – April 7	3 wk before
🎃 Pumpkins	Start indoors	March 30 – April 7	3 wk before
🎃 Summer Squash	Start indoors	March 30 – April 7	3 wk before
🎃 Winter Squash	Start indoors	March 30 – April 7	3 wk before
🥒 Zucchini	Start indoors	March 30 – April 7	3 wk before
🥬 Bok Choy	Direct sow	April 6 – April 14	2 wk before
🥬 Bok Choy	Set out	April 6 – April 14	2 wk before
🥦 Broccoli	Set out	April 6 – April 14	2 wk before
🌿 Cilantro	Direct sow	April 6 – April 14	2 wk before
🥬 Leaf Lettuce	Set out	April 6 – April 14	2 wk before
🥬 Swiss Chard	Direct sow	April 6 – April 14	2 wk before
🥬 Swiss Chard	Set out	April 6 – April 14	2 wk before
🌿 Dill	Direct sow	April 13 – April 21	1 wk before
🫘 Bush Beans	Direct sow	April 27 – May 5	1 wk after
🥒 Cucumbers	Set out	April 27 – May 5	1 wk after
🎃 Pumpkins	Direct sow	April 27 – May 5	1 wk after
🎃 Pumpkins	Set out	April 27 – May 5	1 wk after
🎃 Summer Squash	Direct sow	April 27 – May 5	1 wk after
🎃 Summer Squash	Set out	April 27 – May 5	1 wk after
🌽 Sweet Corn	Direct sow	April 27 – May 5	1 wk after
🍅 Tomatoes	Set out	April 27 – May 5	1 wk after
🎃 Winter Squash	Direct sow	April 27 – May 5	1 wk after
🎃 Winter Squash	Set out	April 27 – May 5	1 wk after
🥒 Zucchini	Direct sow	April 27 – May 5	1 wk after
🥒 Zucchini	Set out	April 27 – May 5	1 wk after
🥒 Cucumbers	Direct sow	May 4 – May 12	2 wk after
🌶️ Okra	Direct sow	May 4 – May 12	2 wk after
🌶️ Okra	Set out	May 4 – May 12	2 wk after
🌶️ Peppers	Set out	May 4 – May 12	2 wk after
🫘 Southern Peas	Direct sow	May 4 – May 12	2 wk after
🍠 Sweet Potato	Set out	May 4 – May 12	2 wk after

Offsets are published guidance; the dates they land on are computed from measured NOAA normals. The seed-starting tool does this for your own ZIP code and counts the days.

What lives through a zone 5b winter

Of 74 perennial edibles, 48 come through a zone 5b winter — and 0 fail here for being too warm rather than too cold, needing more winter chill than this county gets or more heat than they tolerate. Among the ones that work: Cranberry, Honeyberry, Lingonberry, Apple, Aronia, Black Currant, Elderberry, Gooseberry.

Hardiness ranges are a judgement, published by growers rather than measured; the zone they are compared against is measured. On a warm-end verdict, check with your local extension service — a coastal zone 8 and an inland zone 8 are not the same summer.

Cautious — shortens the seasonMedian across stationsOptimistic

Last spring freeze: Plan to May 12 to be careful. Median April 20 – April 28 across 4 stations; April 6 is the optimistic end.
First fall freeze: Plan to September 28 to be careful. Median October 12 – October 20 across 4 stations; October 31 is the optimistic end.

NOAA publishes these as probabilities, not averages — the middle figure is a median, so half of years fall either side of it. The cautious end is the 10% tail: in roughly nine years in ten the freeze falls on the safe side of it.

The 4 stations behind these numbers

All 4 NOAA stations whose normals this page quotes, spanning about 51 km north to south. Every one is named with its identifier in the station list below — this page does not single one out, because no one station speaks for a whole county.

A relative sketch, not a map with a projection: longitude is adjusted for latitude so the shape is not stretched, and there is no basemap. For the one station nearest a specific address, with its real distance, use the ZIP lookup above.

These are the stations this county's ZIP codes actually cite as nearest — not a claim that each one sits inside its boundary, since a rural ZIP legitimately reaches over it. Every figure above comes from them, and each is named so you can check it.

Station	NOAA ID	Last spring freeze	First fall freeze	Season
Altona, IL	USC00110140	April 28	October 12	165 days
Avon, IL	USC00110356	April 22	October 19	177 days
Galesburg, IL	USC00113320	April 20	October 19	180 days
Knoxville, IL	USC00114780	April 21	October 20	181 days

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

Your own ZIP

Work out your own dates

This page describes a whole county. Every tool below answers for one ZIP code, which is the grain the underlying data is published at.

Other places to compare

Knox County sits in Illinois. That page carries the whole state's zone spread, its metro areas, and every other county in it with a page here.

More of Illinois

Counties with the same zones — 5b

Matched on the exact zone set, not a dominant zone, so the winter answer on these pages really is the same one as here.

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.

Trunk wrapZone 5b is cold enough that winter sun on a young trunk does more damage than the cold does.
Row cover and frost clothThe season here closes at the first fall freeze dated above — a cover buys back some of those days at the end.
MulchFor the perennials nearest their cold limit in zone 5b, where an insulated crown is what decides whether they come back.

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

Hardiness zones are the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. Freeze dates and growing-season lengths are NOAA 1991–2020 Climate Normals, taken per station and cited above by name and NOAA ID.

County boundaries come from the Census ZCTA-to-county relation, which is what places each ZIP code — and which treats parishes, boroughs and census areas as county equivalents. No station is chosen to represent this county: every range above is taken across all of them and the count is stated, because picking one would be a judgement dressed as a measurement.