Portsmouth, NH 03903 Frost Dates
When can you plant in Portsmouth, NH?
Around 05/03 is the usual last spring frost, about 248 days away. The first fall frost typically arrives around 10/10, about 158 frost-free days later.
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.
What to do before the first frost
About 6 weeks of growing season left in Portsmouth before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
How much risk comes with planting early here
05/03 is the middle of 30 years of NOAA records, not a promise. Plant by 04/23 and you're betting against frost in roughly 9 years out of 10. 05/16 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Portsmouth compares
At roughly 158 frost-free days, Portsmouth places 32,920 of 40,283 ZIP codes in this dataset. Within NH, it ranks 79 of 260.
Learn more
the frost range covers how to read the range around Portsmouth's dates instead of trusting one. local microclimates covers what one yard in Portsmouth can differ from the 03903 normal.