Williamsburg, IA 52361 Frost Dates
52361, near Williamsburg, IA: the frost window
Around 04/28 is the usual last spring frost, about 243 days away. Fall's first freeze usually shows up around 10/09, roughly 164 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 Williamsburg, not a forecast for this year.
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
At roughly 164 frost-free days, Williamsburg places 30,939 of 40,283 ZIP codes in this dataset. Within IA, it ranks 589 of 1,042.
Learn more
Two guides worth reading on 52361: local microclimates, on what one yard in Williamsburg can differ from the 52361 normal, and zone vs. frost date, on why Zone 5b and Williamsburg's frost date answer different questions.