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Frost Dates in Iowa
First and last frost dates across Iowa, computed from 103 NOAA weather stations (1991–2020 climate normals). Your exact date depends on your city and microclimate — use the ZIP lookup on the main tool for a station-specific answer.
Last spring frost
Apr 28
statewide median · range Apr 10–May 8
First fall frost
Oct 10
statewide median · range Sep 28–Oct 27
Growing season
164 days
median · range 145–198
Stations used
103
NOAA 1991–2020 normals
Frost dates by city
Median dates from the nearest NOAA station to each city. The "cautious" date is the 10% spring value — planting after it means only a ~10% chance of a later frost.
| City | Nearest station | Last spring frost | First fall frost | Growing season | Safe transplant |
|---|---|---|---|---|---|
| Des Moines | Des Moines Intl Ap · 4 mi | Apr 18 (cautious: May 2) | Oct 20 | 184 days | May 2 |
| Cedar Rapids | Cedar Rapids #1 · 6 mi | Apr 28 (cautious: May 13) | Oct 12 | 166 days | May 12 |
| Davenport | Rock Is L&D 15 (IL) · 1 mi | Apr 19 (cautious: May 4) | Oct 22 | 184 days | May 3 |
How frost varies across Iowa
Spring frost timing spans about 28 days across the state. Keokuk 19 in southeastern Iowa typically sees its last spring frost around April 10, while Cresco in northeastern Iowa doesn't clear frost until about May 8. Within any city, low spots and valleys run colder than the station average; areas near buildings and pavement run warmer.
When to plant in Iowa
As a rule of thumb, cool-season crops (lettuce, peas, spinach) can go in 2–4 weeks before your last spring frost; warm-season transplants (tomatoes, peppers) should wait about 2 weeks after it — around May 12 for the statewide median. Check your city's row above rather than the statewide median: a 28-day statewide spread makes the city-level date the one that matters.
These are climate normals (what's typical), not forecasts. For the current year, watch the 10-day forecast around your planting date.
How this is computed
Statewide medians are the median of the 103 NOAA stations' median frost dates — half the stations run earlier, half later. City rows use the nearest station with 30-year freeze records. Dates are 32°F freeze probabilities from NOAA NCEI 1991–2020 U.S. Climate Normals; nothing is estimated or interpolated.
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Frequently asked questions
When is the last frost date in Iowa?
The statewide median last spring frost is April 28, but it ranges from April 10 to May 8 depending on where in the state you are. Use your city's row in the table above, or the ZIP lookup on the main tool, for a station-specific date.
When can I plant tomatoes outside in Iowa?
Warm-season transplants like tomatoes should wait about two weeks after your last spring frost — around May 12 for the statewide median. Your city may differ by weeks; check the "safe transplant" column in the city table.
How long is the growing season in Iowa?
The median growing season across 103 NOAA stations is 164 days, ranging from 145 to 198 days by location.
Why do frost dates vary so much within Iowa?
Frost timing follows latitude, elevation, and local terrain. Across Iowa, last spring frost dates span about 28 days — from around April 10 near Keokuk 19 to May 8 near Cresco. Microclimates (low spots, valleys, urban heat) shift dates further at the garden level.
Where does this data come from?
All frost dates are computed from the NOAA National Centers for Environmental Information 1991–2020 U.S. Climate Normals freeze data (public domain), using each station's 32°F freeze probability statistics. No dates are estimated or interpolated.