Portsmouth, NH 03801 Frost Dates
03801, near Portsmouth, NH: the frost window
Around 05/04 is the usual last spring frost, about 249 days away. Fall's first freeze usually shows up around 10/08, roughly 157 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 Portsmouth, not a forecast for this year.
Stretching the season past the first frost
Portsmouth's growing season runs out in roughly 6 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
05/04 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/23 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/18 and only about 1 year in 10 sees frost after that.
Portsmouth against the rest of the dataset
At roughly 157 frost-free days, Portsmouth places 33,230 of 40,283 ZIP codes in this dataset. Within NH, it ranks 86 of 260.
Learn more
Two guides worth reading on 03801: the frost range, on how to read the range around Portsmouth's dates instead of trusting one, and local microclimates, on what one yard in Portsmouth can differ from the 03801 normal.