Alton, IA 51003 Frost Dates
Alton, IA: when does the frost end?
Typically, the last spring freeze lands around 04/30, roughly 245 days out. Fall's first freeze usually shows up around 10/03, roughly 154 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Alton 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 Alton's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 04/30 isn't a guarantee
04/30 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/17 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/12 and only about 1 year in 10 sees frost after that.
Alton against the rest of the dataset
At roughly 154 frost-free days, Alton places 34,363 of 40,283 ZIP codes in this dataset. Within IA, it ranks 898 of 1,042.
Learn more
Before leaning on 51003's figures: local microclimates explains what one yard in Alton can differ from the 51003 normal, while zone vs. frost date explains why Zone 5a and Alton's frost date answer different questions.