Iowa frost dates

Across Iowa, the average last spring frost is around April 25 and the average first fall frost around October 8 — roughly 166 frost-free days. USDA zones 4b, 5a, 5b.

Risk you accept	Last spring frost by	First fall frost by
Cautious (~10%)	May 9	September 24
Average (~50%)	April 25	October 8
Gambler (~90%)	April 11	October 22

→ Turn these into sowing dates with the Iowa 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.