Williamsburg, IA 52220 Frost Dates
52220, near Williamsburg, IA: the frost window
The last spring frost here typically falls around 04/28, about 243 days from today. Fall's first freeze usually shows up around 10/09, roughly 164 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Williamsburg in Zone 5a (-20 to -15°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
Williamsburg's growing season runs out in roughly 6 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 04/28 isn't a guarantee
04/28 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/14 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/12 and only about 1 year in 10 sees frost after that.
Williamsburg against the rest of the dataset
Williamsburg's growing season runs about 164 days, ranking 30,937 of 40,283 US ZIP codes measured here, longest to shortest. Within IA, it ranks 587 of 1,042.
Learn more
Two guides worth reading on 52220: local microclimates, on what one yard in Williamsburg can differ from the 52220 normal, and zone vs. frost date, on why Zone 5a and Williamsburg's frost date answer different questions.