Alpena, SD 57312 Frost Dates
Frost dates for Alpena, SD, ZIP 57312
Typically, the last spring freeze lands around 05/06, roughly 251 days out. The first fall frost typically arrives around 10/02, about 146 frost-free days later.
Zone 4b (-25 to -20°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 Alpena, not a forecast for this year.
What to do before the first frost
Zone 4b around Alpena has about 5 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
The actual range around Alpena's last frost
05/06 is the middle of 30 years of NOAA records, not a promise. Plant by 04/23 and you're betting against frost in roughly 9 years out of 10. 05/20 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Alpena compares
About 146 days separate Alpena's last and first frost, putting it 36,135 of 40,283 ZIP codes nationally. Within SD, it ranks 221 of 378.
Learn more
the frost range explains how to read the range around Alpena's dates instead of trusting one, and local microclimates explains what one yard in Alpena can differ from the 57312 normal.