Portland, ME 04078 Frost Dates
04078, near Portland, ME: the frost window
Typically, the last spring freeze lands around 04/28, roughly 243 days out. Fall's first freeze usually shows up around 10/19, roughly 172 days after the last spring frost.
Zone 6a (-10 to -5°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 Portland, not a forecast for this year.
Stretching the season past the first frost
Portland'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.
The actual range around Portland's last frost
04/28 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/15 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/10 and only about 1 year in 10 sees frost after that.
Portland against the rest of the dataset
At roughly 172 frost-free days, Portland places 28,140 of 40,283 ZIP codes in this dataset. Within ME, it ranks 75 of 456.
Learn more
Two guides worth reading on 04078: the frost range, on how to read the range around Portland's dates instead of trusting one, and local microclimates, on what one yard in Portland can differ from the 04078 normal.