St. Marys, PA 15857 Frost Dates
15857, near St. Marys, PA: the frost window
Typically, the last spring freeze lands around 05/06, roughly 251 days out. Fall's first freeze usually shows up around 10/14, roughly 160 days after the last spring frost.
Zone 5b (-15 to -10°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 St. Marys, not a forecast for this year.
Stretching the season past the first frost
St. Marys's growing season runs out in roughly 7 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/06 isn't a guarantee
05/06 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 05/23 and only about 1 year in 10 sees frost after that.
St. Marys against the rest of the dataset
At roughly 160 frost-free days, St. Marys places 32,259 of 40,283 ZIP codes in this dataset. Within PA, it ranks 1,690 of 2,088.
Learn more
Two guides worth reading on 15857: local microclimates, on what one yard in St. Marys can differ from the 15857 normal, and zone vs. frost date, on why Zone 5b and St. Marys's frost date answer different questions.