Portsmouth, NH 03911 Frost Dates
Portsmouth, NH: when does the frost end?
The last spring frost here typically falls around 05/04, about 249 days from today. Fall's first freeze usually shows up around 10/08, roughly 157 days after the last spring frost.
Portsmouth sits in USDA Zone 6a (-10 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 6 weeks until Portsmouth's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/04 isn't a guarantee
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
Portsmouth's growing season runs about 157 days, ranking 33,240 of 40,283 US ZIP codes measured here, longest to shortest. Within NH, it ranks 96 of 260.
Learn more
Before leaning on 03911's figures: the frost range explains how to read the range around Portsmouth's dates instead of trusting one, while local microclimates explains what one yard in Portsmouth can differ from the 03911 normal.