Alton, IN 47551 Frost Dates
47551, near Alton, IN: the frost window
The last spring frost here typically falls around 04/11, about 226 days from today. Fall's first freeze usually shows up around 10/26, roughly 197 days after the last spring frost.
Zone 6b (-5 to 0°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 Alton, not a forecast for this year.
Stretching the season past the first frost
Alton's growing season runs out in roughly 8 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
How much risk comes with planting early here
04/11 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 03/27 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 04/30 and only about 1 year in 10 sees frost after that.
Alton against the rest of the dataset
Alton's growing season runs about 197 days, ranking 18,861 of 40,283 US ZIP codes measured here, longest to shortest. Within IN, it ranks 161 of 927.
Learn more
Two guides worth reading on 47551: zone vs. frost date, on why Zone 6b and Alton's frost date answer different questions, and the frost range, on how to read the range around Alton's dates instead of trusting one.