Gardeners are keenly aware of the seasonal effects of temperature, particularly freezing temperatures, on the growth of landscape plants. Terms such as cold hardy, frost hardy, and winter hardy describe plants that can survive varying degrees of freezing temperatures without injury during winter dormancy. Some very large and substantial plants curl their toes and turn mushy if exposed long enough to low temperatures. Imagine a banana tree thriving all summer in Duluth, Minnesota, and then imagine what happens to it in September. On the other hand, some plants can survive freezing — even frigid — temperatures. Some escape the cold by hiding underground or under snow until spring. These plants include the bulbs and many perennials. Others, such as hardy trees and shrubs, undergo metabolic changes between summer and winter.

A plant’s genetic capacity to acclimate determines cold hardiness. When plants acclimate, they transform themselves from a non hardy to hardy condition that allows them to withstand freezing temperatures. But temperature alone isn’t the only criterion of hardiness. Many plants aren’t injured by winter’s minimum temperatures, but in spring and fall as they adjust to changing weather. At those times, while not growing at full tilt, plants aren’t fully hardy, either. Consequently, determining where and when a plant is hardy can be complicated. Temperatures are crucial, but so are a region’s climate patterns and how the plant responds.

Winter injury is easy to diagnose when you see lots of brown leaves on an evergreen plant, injury or death of flower buds, or splitting bark. But, sometimes, damage from winter temperatures is difficult to see, manifested only in delayed bud development or slightly reduced growth.

The safest course to ensure plant adaptability is to grow plants native to your particular region. Such plants most likely have the constitution to survive in your garden. And for the most part, local nurseries stock only plants that are known to survive in their region. Playing it safe isn’t always fun, though. If you want to experiment a little, you need some way to compare the nursery gardens’ climates with the climate where the plant grows well. Zone maps play a critical role here. Most often, when people refer to their growing zone they’re talking about which USDA zone they live in.