Mason City, IA 50401 Frost Dates
Frost dates for Mason City, IA, ZIP 50401
Typically, the last spring freeze lands around 05/03, roughly 248 days out. The first fall frost typically arrives around 10/01, about 150 frost-free days later.
Zone 5a (-20 to -15°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 Mason City, not a forecast for this year.
What to do before the first frost
Zone 5a around Mason City 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 Mason City's last frost
05/03 is the middle of 30 years of NOAA records, not a promise. Plant by 04/19 and you're betting against frost in roughly 9 years out of 10. 05/15 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Mason City compares
Mason City's growing season runs about 150 days, ranking 35,247 of 40,283 US ZIP codes measured here, longest to shortest. Within IA, it ranks 995 of 1,042.
Learn more
local microclimates explains what one yard in Mason City can differ from the 50401 normal, and zone vs. frost date explains why Zone 5a and Mason City's frost date answer different questions.