Groton, SD 57445 Frost Dates
Groton, SD: when does the frost end?
Typically, the last spring freeze lands around 05/06, roughly 251 days out. Fall's first freeze usually shows up around 10/04, roughly 150 days after the last spring frost.
Zone 4a (-30 to -25°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 Groton, not a forecast for this year.
Stretching the season past the first frost
With roughly 5 weeks until Groton's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/06 isn't a guarantee
05/06 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 05/21 and only about 1 year in 10 sees frost after that.
Groton against the rest of the dataset
About 150 days separate Groton's last and first frost, putting it 35,333 of 40,283 ZIP codes nationally. Within SD, it ranks 171 of 378.
Learn more
Before leaning on 57445's figures: zone vs. frost date explains why Zone 4a and Groton's frost date answer different questions, while the frost range explains how to read the range around Groton's dates instead of trusting one.