What USDA hardiness zone is Iowa?

Iowa spans USDA hardiness zones 4b to 6a, from the USDA 2023 Plant Hardiness Zone Map. 57% of its 962 ZIP codes are zone 5a, so there is no single zone for the state.

When is the last spring frost in Iowa?

The median last spring freeze runs April 10 – May 8 across the 150 NOAA stations in Iowa with ordinary freeze windows, from NOAA 1991-2020 Climate Normals. Half of years freeze later than the median.

State guide

Planting zones in Iowa

Iowa spans USDA zones 4b to 6a across its 962 ZIP codes, so there is no single zone for the state and anyone who gives you one is rounding. 57% of its ZIP codes are zone 5a; the rest are not.

USDA zones 4b–6a 4 zones across the state

ZIP codes 962 962 have a NOAA station within range

Weather stations 150 In Iowa, NOAA 1991–2020 normals

Your ZIP code

Get the exact answer for your address

Everything above describes Iowa 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.

Which zone you are in depends where you are

Iowa covers 4 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 57% in zone 5a and wrong for the other 43%. Here is the actual split, by ZIP code.

Zone	ZIP codes	Share
5a	547	57%
5b	371	39%
6a	27	3%
4b	17	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 10 – May 8

First fall freeze September 28 – October 27

Those are the earliest and latest medians among the 150 stations in Iowa 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 150 stations in Iowa it runs 145–198 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 77–85 °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 Iowa 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 Iowa — these are its edges, which is a different claim.

Measure	Earliest / lowest	Station	Latest / highest	Station
Last spring freeze	April 10	Keokuk Lock Dam 19, IA USC00134381	May 8	Elkader 6 Ssw, IA USC00132603
First fall freeze	September 28	Sheldon, IA USC00137594	October 27	Keokuk Lock Dam 19, IA USC00134381
Growing season	145 days	Sheldon, IA USC00137594	198 days	Keokuk Lock Dam 19, IA USC00134381
Mean summer high	77 °F	Northwood, IA USC00136103	85 °F	Lamoni, IA USC00134585

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 Iowa

Every spring job for 63 crop dates, counted from this state's own last spring freeze. Each is a range across all 150 stations — the earliest and latest that job falls anywhere in Iowa — 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 13 – March 13	8 weeks before
Peppers	Start indoors	February 13 – March 13	8 weeks before
Broccoli	Start indoors	February 27 – March 27	6 weeks before
Cabbage	Start indoors	February 27 – March 27	6 weeks before
Collards	Start indoors	February 27 – March 27	6 weeks before
Kale	Start indoors	February 27 – March 27	6 weeks before
Leaf Lettuce	Start indoors	February 27 – March 27	6 weeks before
Peas	Direct sow	February 27 – March 27	6 weeks before
Spinach	Direct sow	February 27 – March 27	6 weeks before
Sweet Potato	Start indoors	February 27 – March 27	6 weeks before
Tomatoes	Start indoors	February 27 – March 27	6 weeks before
Bok Choy	Start indoors	March 6 – April 3	5 weeks before
Kohlrabi	Start indoors	March 6 – April 3	5 weeks before
Swiss Chard	Start indoors	March 6 – April 3	5 weeks before
Arugula	Direct sow	March 13 – April 10	4 weeks before
Baby Salad Greens	Direct sow	March 13 – April 10	4 weeks before
Beets	Direct sow	March 13 – April 10	4 weeks before
Green Onions	Direct sow	March 13 – April 10	4 weeks before
Mustard Greens	Direct sow	March 13 – April 10	4 weeks before
Okra	Start indoors	March 13 – April 10	4 weeks before
Radishes	Direct sow	March 13 – April 10	4 weeks before
Turnips	Direct sow	March 13 – April 10	4 weeks before
Cabbage	Set out	March 20 – April 17	3 weeks before
Carrots	Direct sow	March 20 – April 17	3 weeks before
Collards	Direct sow	March 20 – April 17	3 weeks before
Collards	Set out	March 20 – April 17	3 weeks before
Cucumbers	Start indoors	March 20 – April 17	3 weeks before
Green Onions	Set out	March 20 – April 17	3 weeks before
Kale	Direct sow	March 20 – April 17	3 weeks before
Kale	Set out	March 20 – April 17	3 weeks before
Kohlrabi	Direct sow	March 20 – April 17	3 weeks before
Kohlrabi	Set out	March 20 – April 17	3 weeks before
Leaf Lettuce	Direct sow	March 20 – April 17	3 weeks before
Pumpkins	Start indoors	March 20 – April 17	3 weeks before
Summer Squash	Start indoors	March 20 – April 17	3 weeks before
Winter Squash	Start indoors	March 20 – April 17	3 weeks before
Zucchini	Start indoors	March 20 – April 17	3 weeks before
Bok Choy	Direct sow	March 27 – April 24	2 weeks before
Bok Choy	Set out	March 27 – April 24	2 weeks before
Broccoli	Set out	March 27 – April 24	2 weeks before
Cilantro	Direct sow	March 27 – April 24	2 weeks before
Leaf Lettuce	Set out	March 27 – April 24	2 weeks before
Swiss Chard	Direct sow	March 27 – April 24	2 weeks before
Swiss Chard	Set out	March 27 – April 24	2 weeks before
Dill	Direct sow	April 3 – May 1	1 week before
Bush Beans	Direct sow	April 17 – May 15	1 week after
Cucumbers	Set out	April 17 – May 15	1 week after
Pumpkins	Direct sow	April 17 – May 15	1 week after
Pumpkins	Set out	April 17 – May 15	1 week after
Summer Squash	Direct sow	April 17 – May 15	1 week after
Summer Squash	Set out	April 17 – May 15	1 week after
Sweet Corn	Direct sow	April 17 – May 15	1 week after
Tomatoes	Set out	April 17 – May 15	1 week after
Winter Squash	Direct sow	April 17 – May 15	1 week after
Winter Squash	Set out	April 17 – May 15	1 week after
Zucchini	Direct sow	April 17 – May 15	1 week after
Zucchini	Set out	April 17 – May 15	1 week after
Cucumbers	Direct sow	April 24 – May 22	2 weeks after
Okra	Direct sow	April 24 – May 22	2 weeks after
Okra	Set out	April 24 – May 22	2 weeks after
Peppers	Set out	April 24 – May 22	2 weeks after
Southern Peas	Direct sow	April 24 – May 22	2 weeks after
Sweet Potato	Set out	April 24 – May 22	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 Iowa

Of 74 perennial fruits, nuts, berries, vegetables and herbs, 51 come through the winter in zone 6a and only 34 in zone 4b. Winter hardiness runs on the zone alone, so each row below is exact for the ZIP codes in it.

Zone	ZIPs	Survive
4b	17	34 of 74
5a	547	48 of 74
5b	371	48 of 74
6a	27	51 of 74

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.

What survives my winter?
Runs on the hardiness zone, so it answers exactly for your ZIP code rather than for Iowa as a whole — 74 perennial fruits, berries, vegetables and herbs.
When do I start my seeds?
Dates every spring job from your own last freeze — sow indoors, set out, direct sow.
When do I sow the next round?
How often each crop is worth re-sowing, and when the next sowing is due.
What can I still plant?
Counts the growing days left before your first fall freeze, crop by crop.

Metro areas in Iowa

9 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.

Omaha, NE-IA Zones 5a–6a
Des Moines-West Des Moines, IA Zones 5a–5b
Davenport-Moline-Rock Island, IA-IL Zone 5b
Cedar Rapids, IA Zones 5a–5b
Sioux City, IA-NE-SD Zone 5a
Waterloo-Cedar Falls, IA Zone 5a
Ames, IA Zones 5a–5b
Iowa City, IA Zones 5a–5b
Dubuque, IA Zone 5a

Counties in Iowa

19 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 Iowa'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.

Trunk wrapZone 4b 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 4b, 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

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 Iowa. Which ZIP codes are in Iowa 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 Iowa 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.

All states · All metro areas