Iowa City, IA 52240 Frost Dates
52240, near Iowa City, IA: the frost window
The last spring frost here typically falls around 04/21, about 236 days from today. Fall's first freeze usually shows up around 10/18, roughly 180 days after the last spring frost.
Zone 5b (-15 to -10°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Iowa City, not a forecast for this year.
Stretching the season past the first frost
Iowa City's growing season runs out in roughly 7 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 04/21 isn't a guarantee
04/21 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/05 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/06 and only about 1 year in 10 sees frost after that.
Iowa City against the rest of the dataset
About 180 days separate Iowa City's last and first frost, putting it 24,762 of 40,283 ZIP codes nationally. Within IA, it ranks 86 of 1,042.
Learn more
Two guides worth reading on 52240: local microclimates, on what one yard in Iowa City can differ from the 52240 normal, and zone vs. frost date, on why Zone 5b and Iowa City's frost date answer different questions.