Hecla, SD 57446 Frost Dates
Frost dates for Hecla, SD, ZIP 57446
Typically, the last spring freeze lands around 05/09, roughly 254 days out. The first fall frost typically arrives around 09/28, about 141 frost-free days later.
Hecla sits in USDA Zone 4a (-30 to -25°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
What to do before the first frost
Zone 4a around Hecla has about 4 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.
Why 05/09 isn't a guarantee
05/09 is the middle of 30 years of NOAA records, not a promise. Plant by 04/27 and you're betting against frost in roughly 9 years out of 10. 05/23 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Hecla compares
At roughly 141 frost-free days, Hecla places 36,998 of 40,283 ZIP codes in this dataset. Within SD, it ranks 304 of 378.
Learn more
the frost range explains how to read the range around Hecla's dates instead of trusting one, and local microclimates explains what one yard in Hecla can differ from the 57446 normal.