Alton, IL 62002 Frost Dates
Alton, IL: when does the frost end?
Typically, the last spring freeze lands around 04/04, roughly 219 days out. Fall's first freeze usually shows up around 11/05, roughly 214 days after the last spring frost.
Alton sits in USDA Zone 7a (0 to 5°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
Stretching the season past the first frost
With roughly 10 weeks until Alton's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 04/04 isn't a guarantee
04/04 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 03/18 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 04/19 and only about 1 year in 10 sees frost after that.
Alton against the rest of the dataset
At roughly 214 frost-free days, Alton places 14,229 of 40,283 ZIP codes in this dataset. Within IL, it ranks 9 of 1,548.
Learn more
Before leaning on 62002's figures: zone vs. frost date explains why Zone 7a and Alton's frost date answer different questions, while the frost range explains how to read the range around Alton's dates instead of trusting one.