Iroquois, SD 57353 Frost Dates
57353, near Iroquois, SD: the frost window
Typically, the last spring freeze lands around 05/05, roughly 250 days out. Fall's first freeze usually shows up around 10/04, roughly 151 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Iroquois in Zone 4b (-25 to -20°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
Iroquois'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.
Why 05/05 isn't a guarantee
05/05 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/22 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/20 and only about 1 year in 10 sees frost after that.
Iroquois against the rest of the dataset
At roughly 151 frost-free days, Iroquois places 35,162 of 40,283 ZIP codes in this dataset. Within SD, it ranks 159 of 378.
Learn more
Two guides worth reading on 57353: local microclimates, on what one yard in Iroquois can differ from the 57353 normal, and zone vs. frost date, on why Zone 4b and Iroquois's frost date answer different questions.