Portsmouth, NH 03854 Frost Dates
Portsmouth, NH: when does the frost end?
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.
The USDA Plant Hardiness Zone Map puts Portsmouth in Zone 6a (-10 to -5°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's 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.
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 33,232 of 40,283 ZIP codes in this dataset. Within NH, it ranks 88 of 260.
Learn more
Before leaning on 03854's figures: zone vs. frost date explains why Zone 6a and Portsmouth's frost date answer different questions, while the frost range explains how to read the range around Portsmouth's dates instead of trusting one.