Wisconsin frost dates

Across Wisconsin, the average last spring frost is around May 10 and the average first fall frost around September 30 — roughly 143 frost-free days. USDA zones 3b, 4a, 4b, 5a, 5b.

Risk you accept	Last spring frost by	First fall frost by
Cautious (~10%)	May 24	September 16
Average (~50%)	May 10	September 30
Gambler (~90%)	April 26	October 14

→ Turn these into sowing dates with the Wisconsin 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.