Ottosen, IA 50570 Frost Dates
50570, near Ottosen, IA: the frost window
Typically, the last spring freeze lands around 04/26, roughly 241 days out. Fall's first freeze usually shows up around 10/12, roughly 169 days after the last spring frost.
Zone 5a (-20 to -15°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 Ottosen, not a forecast for this year.
Stretching the season past the first frost
Ottosen'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 04/26 isn't a guarantee
04/26 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/11 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/07 and only about 1 year in 10 sees frost after that.
Ottosen against the rest of the dataset
At roughly 169 frost-free days, Ottosen places 29,639 of 40,283 ZIP codes in this dataset. Within IA, it ranks 365 of 1,042.
Learn more
Two guides worth reading on 50570: local microclimates, on what one yard in Ottosen can differ from the 50570 normal, and zone vs. frost date, on why Zone 5a and Ottosen's frost date answer different questions.