South Dakota frost dates

Across South Dakota, the average last spring frost is around May 10 and the average first fall frost around September 25 — roughly 138 frost-free days. USDA zones 3b, 4a, 4b, 5a.

Risk you accept	Last spring frost by	First fall frost by
Cautious (~10%)	May 24	September 11
Average (~50%)	May 10	September 25
Gambler (~90%)	April 26	October 9

→ Turn these into sowing dates with the South Dakota planting calendar, or look up an exact ZIP code.

Statewide average from NOAA/NCEI freeze normals. Cautious/gambler dates are about two weeks either side of the average.