What USDA hardiness zone is Marshall County, Iowa?

Marshall County, Iowa spans USDA hardiness zones 5a to 5b. 77% of its ZIP codes are zone 5a, so there is no single zone for the county.

When is the last spring frost in Marshall County, Iowa?

The median last spring freeze runs April 22 – May 3 across the 5 NOAA weather stations serving Marshall County, Iowa, from NOAA 1991-2020 Climate Normals. Half of years freeze later than the median.

Iowa

Planting zones in Marshall County, Iowa

This county spans USDA zones 5a to 5b, so there is no single zone for Marshall County and anyone who gives you one is rounding. 77% of its ZIP codes are zone 5a; the rest are not.

USDA zones 5a–5b 2 zones across 13 ZIP codes

ZIP codes 13 13 have a NOAA station within range

Weather stations 5 NOAA 1991–2020 normals, across 573 sq mi

Your ZIP code

Get the exact answer for your address

Everything above describes Marshall County, 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.

The growing season in Marshall County is closing

Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives October 6 – October 17 across the 5 NOAA stations serving this county .

Your next season already has a date

The first job of it is 🧅 Green Onions, start indoors, around February 25 – March 8 — counted back from a last spring freeze of April 22 – May 3 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 5 stations agreeAt least one station

Every one of the 5 NOAA stations serving this county counts May 3 – October 6 as growing season (156 days). Widening to any single station gives April 22 – October 17 (178 days).

That is a 22-day difference inside one county — which is why this page gives ranges rather than a single planting date. The ZIP lookup above resolves it to one station.

Which zone you are in depends where you are

Marshall County covers 2 hardiness zones. A guide that gives the county one zone has picked whichever is largest and rounded everyone else into it — fine for the 77% in zone 5a and wrong for the other 23%. Here is the actual split.

Zone	ZIP codes	Share
5a	10	77%
5b	3	23%

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

Your freeze dates

Last spring freeze April 22 – May 3

First fall freeze October 6 – October 17

Across the 5 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 155–174 days depending which station you are nearest, as published by NOAA rather than computed from the dates above. Summer highs average 81.3–82.8 °F in June–August. Summer rain over the same months runs 12.9–14.9" across those 5 stations, against the rough inch a week — about 13 inches over the same 92 days — that a vegetable garden is usually reckoned to want. At the middle station that is covered, so watering in Marshall County is for the gaps between storms rather than the whole season. 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 Marshall 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
50005	5a	Marshalltown Muni AP, IA	9.9 km
50051	5a	Marshalltown Muni AP, IA	18.6 km
50078	5a	Marshalltown, IA	14.9 km
50106	5a	Grinnell 3 SW, IA	18.5 km
50120	5a	Marshalltown, IA	15.3 km
50141	5b	Newton, IA	18.6 km
50142	5a	Marshalltown, IA	13.9 km
50148	5a	Marshalltown Muni AP, IA	10.0 km
50158	5a	Marshalltown, IA	2.6 km
50162	5b	Marshalltown, IA	19.0 km
50234	5b	Colo, IA	18.3 km
50239	5a	Colo, IA	17.0 km
50247	5a	Colo, IA	12.6 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 Marshall County

Every date below is anchored on the last spring freeze at each station and reported as a range across all 5 of them, because no one station speaks for the county.

Crop	Job	When	Offset
🧅 Green Onions	Start indoors	February 25 – March 8	8 wk before
🌶️ Peppers	Start indoors	February 25 – March 8	8 wk before
🥦 Broccoli	Start indoors	March 11 – March 22	6 wk before
🥬 Cabbage	Start indoors	March 11 – March 22	6 wk before
🥬 Collards	Start indoors	March 11 – March 22	6 wk before
🥬 Kale	Start indoors	March 11 – March 22	6 wk before
🥬 Leaf Lettuce	Start indoors	March 11 – March 22	6 wk before
🫛 Peas	Direct sow	March 11 – March 22	6 wk before
🥬 Spinach	Direct sow	March 11 – March 22	6 wk before
🍠 Sweet Potato	Start indoors	March 11 – March 22	6 wk before
🍅 Tomatoes	Start indoors	March 11 – March 22	6 wk before
🥬 Bok Choy	Start indoors	March 18 – March 29	5 wk before
🥬 Kohlrabi	Start indoors	March 18 – March 29	5 wk before
🥬 Swiss Chard	Start indoors	March 18 – March 29	5 wk before
🥬 Arugula	Direct sow	March 25 – April 5	4 wk before
🥬 Baby Salad Greens	Direct sow	March 25 – April 5	4 wk before
🥕 Beets	Direct sow	March 25 – April 5	4 wk before
🧅 Green Onions	Direct sow	March 25 – April 5	4 wk before
🥬 Mustard Greens	Direct sow	March 25 – April 5	4 wk before
🌶️ Okra	Start indoors	March 25 – April 5	4 wk before
🌱 Radishes	Direct sow	March 25 – April 5	4 wk before
🥔 Turnips	Direct sow	March 25 – April 5	4 wk before
🥬 Cabbage	Set out	April 1 – April 12	3 wk before
🥕 Carrots	Direct sow	April 1 – April 12	3 wk before
🥬 Collards	Direct sow	April 1 – April 12	3 wk before
🥬 Collards	Set out	April 1 – April 12	3 wk before
🥒 Cucumbers	Start indoors	April 1 – April 12	3 wk before
🧅 Green Onions	Set out	April 1 – April 12	3 wk before
🥬 Kale	Direct sow	April 1 – April 12	3 wk before
🥬 Kale	Set out	April 1 – April 12	3 wk before
🥬 Kohlrabi	Direct sow	April 1 – April 12	3 wk before
🥬 Kohlrabi	Set out	April 1 – April 12	3 wk before
🥬 Leaf Lettuce	Direct sow	April 1 – April 12	3 wk before
🎃 Pumpkins	Start indoors	April 1 – April 12	3 wk before
🎃 Summer Squash	Start indoors	April 1 – April 12	3 wk before
🎃 Winter Squash	Start indoors	April 1 – April 12	3 wk before
🥒 Zucchini	Start indoors	April 1 – April 12	3 wk before
🥬 Bok Choy	Direct sow	April 8 – April 19	2 wk before
🥬 Bok Choy	Set out	April 8 – April 19	2 wk before
🥦 Broccoli	Set out	April 8 – April 19	2 wk before
🌿 Cilantro	Direct sow	April 8 – April 19	2 wk before
🥬 Leaf Lettuce	Set out	April 8 – April 19	2 wk before
🥬 Swiss Chard	Direct sow	April 8 – April 19	2 wk before
🥬 Swiss Chard	Set out	April 8 – April 19	2 wk before
🌿 Dill	Direct sow	April 15 – April 26	1 wk before
🫘 Bush Beans	Direct sow	April 29 – May 10	1 wk after
🥒 Cucumbers	Set out	April 29 – May 10	1 wk after
🎃 Pumpkins	Direct sow	April 29 – May 10	1 wk after
🎃 Pumpkins	Set out	April 29 – May 10	1 wk after
🎃 Summer Squash	Direct sow	April 29 – May 10	1 wk after
🎃 Summer Squash	Set out	April 29 – May 10	1 wk after
🌽 Sweet Corn	Direct sow	April 29 – May 10	1 wk after
🍅 Tomatoes	Set out	April 29 – May 10	1 wk after
🎃 Winter Squash	Direct sow	April 29 – May 10	1 wk after
🎃 Winter Squash	Set out	April 29 – May 10	1 wk after
🥒 Zucchini	Direct sow	April 29 – May 10	1 wk after
🥒 Zucchini	Set out	April 29 – May 10	1 wk after
🥒 Cucumbers	Direct sow	May 6 – May 17	2 wk after
🌶️ Okra	Direct sow	May 6 – May 17	2 wk after
🌶️ Okra	Set out	May 6 – May 17	2 wk after
🌶️ Peppers	Set out	May 6 – May 17	2 wk after
🫘 Southern Peas	Direct sow	May 6 – May 17	2 wk after
🍠 Sweet Potato	Set out	May 6 – May 17	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 survives the winter changes across Marshall County

Zone 5a carries 48 of 74 perennial edibles; zone 5a carries 48.

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 17 to be careful. Median April 22 – May 3 across 5 stations; April 8 is the optimistic end.
First fall freeze: Plan to September 22 to be careful. Median October 6 – October 17 across 5 stations; October 28 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 5 stations behind these numbers

All 5 NOAA stations whose normals this page quotes, spanning about 45 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
Colo, IA	USC00131710	April 24	October 12	170 days
Grinnell 3 SW, IA	USC00133473	May 3	October 6	155 days
Marshalltown Muni AP, IA	USW00094988	April 30	October 6	159 days
Marshalltown, IA	USC00135198	April 28	October 7	162 days
Newton, IA	USC00135992	April 22	October 17	174 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

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

More of Iowa

Counties with the same zones — 5a–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 5a 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 5a, 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.