Plant hardiness is a measure of its tolerance to cold. Plants that can withstand greater cold during winter without being damaged are said to have greater hardiness. For example, paper birch and white spruce trees that survive the very cold winters of Alaska are much hardier than palm trees that can’t tolerate freezing temperatures.
Plant Hardiness Zones divide the United States and Canada into 11 areas based on 10°F differences in the average annual minimum temperature (the United States falls within Zones 2 through 10). For example, the lowest average temperature for Zone 2 is -50 to -40°F, while the lowest average temperature for zone 10 is +30 to +40°F. Each Hardiness Zone is further subdivided into zone a and b based on increments of 5°F. For example, Zones 2a and 2b range from -50 to -45°F and -45 to -40°F, respectively.Plant Hardiness Zones divide the United States and Canada into 11 areas based on 10°F differences in the average annual minimum temperature (the United States falls within Zones 2 through 10). For example, the lowest average temperature for Zone 2 is -50 to -40°F, while the lowest average temperature for zone 10 is +30 to +40°F. Each Hardiness Zone is further subdivided into zone a and b based on increments of 5°F. For example, Zones 2a and 2b range from -50 to -45°F and -45 to -40°F, respectively.
Most trees, shrubs, and perennials have been evaluated for their winter hardiness. If a range of zones, for example, zones 4-9, is indicated, the plant is known to be hardy in zones 4, 5, 6, 7, 8, and 9. Suitable hardiness means a plant can be expected to grow in the zone’s temperature extremes, as determined by the lowest average annual temperature. Maps of Plant Hardiness Zones are useful guides to aid in the selection of trees for planting in your community
(see more).
Keep in mind that local variation in precipitation, soil, wind, and other conditions also affect the viability of individual plants. You may want to ask a
local professional arborist
or nursery about which trees to plant in your locality.