New Hampshire climate

New Hampshire Plant Hardiness Zones

New Hampshire’s towns run from zone 4a to zone 6b: the average coldest winter night is -3.7°F at Seabrook Beach and -27.6°F at Columbia.

Hardiness zones in New Hampshire

In USDA’s colors, neighboring states washed out. Zones follow elevation, coasts and cities down to half a mile. Drawn by WeatherOverTime from the USDA-ARS and Oregon State University PRISM Climate Group 2023 GIS data; this is not the official USDA Plant Hardiness Zone Map.

Map of the 2023 plant hardiness zones across New Hampshire, from zone 3b to zone 6b, with the state’s border drawn.
  • 3b
  • 4a
  • 4b
  • 5a
  • 5b
  • 6a
  • 6b

Open the live map with plant hardiness zones

Towns by zone

Each town’s 1991-2020 average annual extreme minimum at its center, read from the map’s 800 m grid. Warmest zone first.

6b Zone 6b, -5 to 0°F 4 towns

6a Zone 6a, -10 to -5°F 92 towns

5b Zone 5b, -15 to -10°F 69 towns

5a Zone 5a, -20 to -15°F 39 towns

4b Zone 4b, -25 to -20°F 10 towns

4a Zone 4a, -30 to -25°F 7 towns

Counties

At the county’s center; a county with hills or a coast spans several zones.

CountyZone at the centerAverage coldest night
Belknap County5b-12.4°F
Carroll County5a-15.6°F
Cheshire County5b-11.7°F
Coos County4b-23.4°F
Grafton County5b-14.7°F
Hillsborough County6a-8.8°F
Merrimack County5b-12°F
Rockingham County6a-7.6°F
Strafford County6a-8.9°F
Sullivan County5a-16.9°F

The zones

A plant hardiness zone is set by the average of each winter’s single coldest temperature, 1991 to 2020: zones are 10°F apart and each half zone, a and b, 5°F. It says how cold a winter night usually gets, not the coldest it has ever been, and nothing about summer heat, rain or soil. Plant labels give the coldest zone a perennial survives in.

ZoneAverage coldest nightIn Celsius
4a-30 to -25°F-34.4 to -31.7°C
4b-25 to -20°F-31.7 to -28.9°C
5a-20 to -15°F-28.9 to -26.1°C
5b-15 to -10°F-26.1 to -23.3°C
6a-10 to -5°F-23.3 to -20.6°C
6b-5 to 0°F-20.6 to -17.8°C

Sources

Hardiness zones: USDA Plant Hardiness Zone Map, 2023, Agricultural Research Service, U.S. Department of Agriculture, from the GIS data of the PRISM Climate Group, Oregon State University, which may be freely reproduced and redistributed. Drawn by WeatherOverTime from the USDA-ARS and Oregon State University PRISM Climate Group 2023 GIS data; this is not the official USDA Plant Hardiness Zone Map.