Mason City, IA 50402 Frost Dates
Mason City, IA: when does the frost end?
Typically, the last spring freeze lands around 05/03, roughly 248 days out. Fall's first freeze usually shows up around 10/01, roughly 150 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Mason City in Zone 5a (-20 to -15°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
With roughly 5 weeks until Mason City's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/03 isn't a guarantee
05/03 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/19 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/15 and only about 1 year in 10 sees frost after that.
Mason City against the rest of the dataset
Mason City's growing season runs about 150 days, ranking 35,248 of 40,283 US ZIP codes measured here, longest to shortest. Within IA, it ranks 996 of 1,042.
Learn more
Before leaning on 50402's figures: the frost range explains how to read the range around Mason City's dates instead of trusting one, while local microclimates explains what one yard in Mason City can differ from the 50402 normal.