Williamson, IA 50272 Frost Dates
50272, near Williamson, IA: the frost window
Around 05/05 is the usual last spring frost, about 250 days away. Fall's first freeze usually shows up around 10/05, roughly 151 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 Williamson, not a forecast for this year.
Stretching the season past the first frost
Williamson's growing season runs out in roughly 5 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
How much risk comes with planting early here
05/05 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/21 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/19 and only about 1 year in 10 sees frost after that.
Williamson against the rest of the dataset
At roughly 151 frost-free days, Williamson places 35,190 of 40,283 ZIP codes in this dataset. Within IA, it ranks 988 of 1,042.
Learn more
Two guides worth reading on 50272: the frost range, on how to read the range around Williamson's dates instead of trusting one, and local microclimates, on what one yard in Williamson can differ from the 50272 normal.