Connecticut climate

Connecticut Plant Hardiness Zones

Connecticut’s towns run from zone 6a to zone 7b: the average coldest winter night is 5.7°F at Old Greenwich and -9.4°F at Canaan.

Hardiness zones in Connecticut

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 Connecticut, from zone 6a to zone 7b, with the state’s border drawn.
  • 6a
  • 6b
  • 7a
  • 7b

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.

7b Zone 7b, 5 to 10°F 6 towns

7a Zone 7a, 0 to 5°F 55 towns

6b Zone 6b, -5 to 0°F 110 towns

6a Zone 6a, -10 to -5°F 27 towns

Counties

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

CountyZone at the centerAverage coldest night
Capitol Planning Region6b-0.7°F
Greater Bridgeport Planning Region7a0.9°F
Lower Connecticut River Valley Planning Region6b-1.1°F
Naugatuck Valley Planning Region6b-2.3°F
Northeastern Connecticut Planning Region6b-3.4°F
Northwest Hills Planning Region6a-7.5°F
South Central Connecticut Planning Region7a0.7°F
Southeastern Connecticut Planning Region6b-0.3°F
Western Connecticut Planning Region6b-2.5°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
6a-10 to -5°F-23.3 to -20.6°C
6b-5 to 0°F-20.6 to -17.8°C
7a0 to 5°F-17.8 to -15.0°C
7b5 to 10°F-15.0 to -12.2°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.