Place guide
Planting zones in Iowa City, IA
This metro spans USDA zones 5a to 5b, so there is no single zone for Iowa City, IA and anyone who gives you one is rounding. 95% of its ZIP codes are zone 5b; the rest are not.
Your ZIP code
Get the exact answer for your address
Everything above describes Iowa City, IA 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 Iowa City, IA is closing
Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives October 9 – October 18 across the 5 NOAA stations serving this metro area .
Your next season already has a date
The first job of it is 🧅 Green Onions, start indoors, around February 24 – March 4 — counted back from a last spring freeze of April 21 – April 29 here.
These are ranges across the whole metro area. 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 metro area counts April 29 – October 9 as growing season (163 days). Widening to any single station gives April 21 – October 18 (180 days).
Which zone you are in depends where you are
Iowa City, IA covers 2 hardiness zones. A guide that gives the metro one zone has picked whichever is largest and rounded everyone else into it — which is fine for the 95% in zone 5b and wrong for the other 5%. Here is the actual split.
| Zone | ZIP codes | Share | |
|---|---|---|---|
| 5b | 19 | 95% | |
| 5a | 1 | 5% |
Zones are published per ZIP code, so yours is exact even though the metro's is not. The hardiness tool will tell you which one you are in.
Your freeze dates
Those are the earliest and latest medians among the 5 stations serving this metro — not an average, and not one station standing in for the rest. Half of years freeze later than a station's own median.
The spread is the point. Even in a metro that is one hardiness zone throughout, its stations disagree about the last spring freeze. Hardiness zone and frost date measure different things — a zone is the average annual coldest night, a freeze date is when the season turns — and a place can be uniform in one and varied in the other. Use the tools below with your own ZIP rather than the ends of this range.
Your growing season
NOAA publishes a growing-season length for each station, and across the 5 stations serving Iowa City, IA it runs 162–180 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 81–84 °F , below the 90 °F point where cool-season crops reliably bolt. Summer rain over the same months runs 13.1–14.4" 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 Iowa City, IA 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 83 °F summer afternoon drying the soil faster than a cool one.
When to start seeds in Iowa City, IA
Every spring job for 63 crop dates, counted from this metro's own last spring freeze. Each is a range across all 5 stations — the earliest and latest that job falls anywhere in the metro — because no one station speaks for the whole area.
| Crop | Job | When | Offset |
|---|---|---|---|
| Green Onions | Start indoors | February 24 – March 4 | 8 weeks before |
| Peppers | Start indoors | February 24 – March 4 | 8 weeks before |
| Broccoli | Start indoors | March 10 – March 18 | 6 weeks before |
| Cabbage | Start indoors | March 10 – March 18 | 6 weeks before |
| Collards | Start indoors | March 10 – March 18 | 6 weeks before |
| Kale | Start indoors | March 10 – March 18 | 6 weeks before |
| Leaf Lettuce | Start indoors | March 10 – March 18 | 6 weeks before |
| Peas | Direct sow | March 10 – March 18 | 6 weeks before |
| Spinach | Direct sow | March 10 – March 18 | 6 weeks before |
| Sweet Potato | Start indoors | March 10 – March 18 | 6 weeks before |
| Tomatoes | Start indoors | March 10 – March 18 | 6 weeks before |
| Bok Choy | Start indoors | March 17 – March 25 | 5 weeks before |
| Kohlrabi | Start indoors | March 17 – March 25 | 5 weeks before |
| Swiss Chard | Start indoors | March 17 – March 25 | 5 weeks before |
| Arugula | Direct sow | March 24 – April 1 | 4 weeks before |
| Baby Salad Greens | Direct sow | March 24 – April 1 | 4 weeks before |
| Beets | Direct sow | March 24 – April 1 | 4 weeks before |
| Green Onions | Direct sow | March 24 – April 1 | 4 weeks before |
| Mustard Greens | Direct sow | March 24 – April 1 | 4 weeks before |
| Okra | Start indoors | March 24 – April 1 | 4 weeks before |
| Radishes | Direct sow | March 24 – April 1 | 4 weeks before |
| Turnips | Direct sow | March 24 – April 1 | 4 weeks before |
| Cabbage | Set out | March 31 – April 8 | 3 weeks before |
| Carrots | Direct sow | March 31 – April 8 | 3 weeks before |
| Collards | Direct sow | March 31 – April 8 | 3 weeks before |
| Collards | Set out | March 31 – April 8 | 3 weeks before |
| Cucumbers | Start indoors | March 31 – April 8 | 3 weeks before |
| Green Onions | Set out | March 31 – April 8 | 3 weeks before |
| Kale | Direct sow | March 31 – April 8 | 3 weeks before |
| Kale | Set out | March 31 – April 8 | 3 weeks before |
| Kohlrabi | Direct sow | March 31 – April 8 | 3 weeks before |
| Kohlrabi | Set out | March 31 – April 8 | 3 weeks before |
| Leaf Lettuce | Direct sow | March 31 – April 8 | 3 weeks before |
| Pumpkins | Start indoors | March 31 – April 8 | 3 weeks before |
| Summer Squash | Start indoors | March 31 – April 8 | 3 weeks before |
| Winter Squash | Start indoors | March 31 – April 8 | 3 weeks before |
| Zucchini | Start indoors | March 31 – April 8 | 3 weeks before |
| Bok Choy | Direct sow | April 7 – April 15 | 2 weeks before |
| Bok Choy | Set out | April 7 – April 15 | 2 weeks before |
| Broccoli | Set out | April 7 – April 15 | 2 weeks before |
| Cilantro | Direct sow | April 7 – April 15 | 2 weeks before |
| Leaf Lettuce | Set out | April 7 – April 15 | 2 weeks before |
| Swiss Chard | Direct sow | April 7 – April 15 | 2 weeks before |
| Swiss Chard | Set out | April 7 – April 15 | 2 weeks before |
| Dill | Direct sow | April 14 – April 22 | 1 week before |
| Bush Beans | Direct sow | April 28 – May 6 | 1 week after |
| Cucumbers | Set out | April 28 – May 6 | 1 week after |
| Pumpkins | Direct sow | April 28 – May 6 | 1 week after |
| Pumpkins | Set out | April 28 – May 6 | 1 week after |
| Summer Squash | Direct sow | April 28 – May 6 | 1 week after |
| Summer Squash | Set out | April 28 – May 6 | 1 week after |
| Sweet Corn | Direct sow | April 28 – May 6 | 1 week after |
| Tomatoes | Set out | April 28 – May 6 | 1 week after |
| Winter Squash | Direct sow | April 28 – May 6 | 1 week after |
| Winter Squash | Set out | April 28 – May 6 | 1 week after |
| Zucchini | Direct sow | April 28 – May 6 | 1 week after |
| Zucchini | Set out | April 28 – May 6 | 1 week after |
| Cucumbers | Direct sow | May 5 – May 13 | 2 weeks after |
| Okra | Direct sow | May 5 – May 13 | 2 weeks after |
| Okra | Set out | May 5 – May 13 | 2 weeks after |
| Peppers | Set out | May 5 – May 13 | 2 weeks after |
| Southern Peas | Direct sow | May 5 – May 13 | 2 weeks after |
| Sweet Potato | Set out | May 5 – May 13 | 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 City, IA
Of 74 perennial fruits, nuts, berries, vegetables and herbs, 48 come through the winter in every zone this metro covers.
| Zone | ZIPs | Survive | Fail for being too warm |
|---|---|---|---|
| 5a | 1 | 48 of 74 | 0 |
| 5b | 19 | 48 of 74 | 0 |
The last column is the counterintuitive one, and it is why the totals do not simply rise as the winters get milder. 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.
Cautious — shortens the seasonMedian across stationsOptimistic
- Last spring freeze
- Plan to May 14 to be careful. Median April 21 – April 29 across 5 stations; April 5 is the optimistic end.
- First fall freeze
- Plan to September 23 to be careful. Median October 9 – October 18 across 5 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 5 stations behind these numbers
All 5 NOAA stations whose normals this page quotes, spanning about 67 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 metro area.
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.
Every figure above comes from these, and each is named so you can check it. Which station serves a given ZIP code, and how far away it is, varies across the metro — the table below gives it per ZIP code rather than this page averaging it.
| Station | NOAA ID | Last spring freeze | First fall freeze | Season |
|---|---|---|---|---|
| Cedar Rapids Muni AP, IA | USW00014990 | April 27 | October 11 | 165 days |
| Columbus Junction, IA | USC00131731 | April 26 | October 10 | 167 days |
| Iowa City Muni AP, IA | USW00014937 | April 21 | October 18 | 180 days |
| Iowa City, IA | USC00134101 | April 29 | October 9 | 162 days |
| Washington, IA | USC00138688 | April 28 | October 11 | 165 days |
These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.
Every ZIP code in Iowa City, IA
Zones are published per ZIP code, not per metro area, so this is the exact answer rather than the metro area'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 |
|---|---|---|---|
| 52201 | 5b | Washington, IA | 14.4 km |
| 52235 | 5b | Iowa City, IA | 4.1 km |
| 52240 | 5b | Iowa City, IA | 2.5 km |
| 52241 | 5b | Iowa City Muni AP, IA | 8.5 km |
| 52242 | 5b | Iowa City Muni AP, IA | 3.4 km |
| 52245 | 5b | Iowa City Muni AP, IA | 5.1 km |
| 52246 | 5b | Iowa City Muni AP, IA | 4.8 km |
| 52247 | 5b | Iowa City Muni AP, IA | 19.6 km |
| 52248 | 5b | Washington, IA | 20.3 km |
| 52317 | 5b | Cedar Rapids Muni AP, IA | 14.6 km |
| 52322 | 5b | Iowa City Muni AP, IA | 19.4 km |
| 52327 | 5b | Iowa City, IA | 16.1 km |
| 52333 | 5b | Iowa City Muni AP, IA | 19.6 km |
| 52338 | 5a | Cedar Rapids Muni AP, IA | 7.3 km |
| 52340 | 5b | Iowa City Muni AP, IA | 13.7 km |
| 52353 | 5b | Washington, IA | 1.9 km |
| 52356 | 5b | Washington, IA | 24.4 km |
| 52359 | 5b | Washington, IA | 11.7 km |
| 52621 | 5b | Columbus Junction, IA | 16.5 km |
| 52755 | 5b | Iowa City, IA | 15.6 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.
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.
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What survives my winter?
Runs on the hardiness zone, so it answers for all of Iowa City, IA at once — zone across 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.
Other places to compare
These metros span exactly the same zones — 5a–5b — so the same plants are in and out of range across them. The freeze dates and the spring calendar are their own.
- Fort Collins-Loveland, CO — zones 5a–5b
- Fond du Lac, WI — zones 5a–5b
- Cheyenne, WY — zones 5a–5b
- Janesville-Beloit, WI — zones 5a–5b
- Oshkosh-Neenah, WI — zones 5a–5b
- Des Moines-West Des Moines, IA — zones 5a–5b
- Madison, WI — zones 5a–5b
- Cedar Rapids, IA — zones 5a–5b
Gardening in Iowa — zones 4b– 6a covers the whole state: how its 962 ZIP codes divide between 4 hardiness zones, and the freeze dates across every NOAA station in it.
Other metro areas in IA:
- Dubuque, IA Zone 5a
- 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
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
The hardiness zone is the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. The freeze dates are NOAA's 1991–2020 Climate Normals, read from every station whose normals cover a ZIP code in this metro. Nothing here is estimated, and no station stands in for another.
This page names no single station on purpose. Picking one to represent a metro sounds reasonable and is not: the station serving the most ZIP codes is an artifact of where ZIP centroids happen to fall, and it selects a lock on the Monongahela for Pittsburgh and a far southern suburb for Chicago. A range across every station is true; a single cited date for a whole metro is not.