Plant Hardiness Zones are the planting zones that indicate the difference in temperature. The USDA map gives Zones 1 through 11 with 11 being the warmest and 1 the coldest. The United States is broken down into Zones 2 through 10. These zones give useful information that tell you what trees can be expected to survive in your area.
Zone 1, the coldest area on the hardiness map, contains the area of extreme Northern Canada, Saskatchewan, portions of Alaska and the Yukon Territory. Trees that can survive in these regions must tolerate temperatures that reach as low as minus 50 degrees F. Tree choices for Zone 1 include the dwarf birch and the cedar tree.
The Zone 2 hardiness zones contain portions of northern Canada, portions of Alaska and the very highest elevations of Wyoming and Montana. Temperatures can reach as low as minus 50 degrees F. The growing season is short, but they experience warmer temperatures around the large bodies of water, such as the Bering Sea. Trees for Zone 2 include Colorado spruce, jack pine and the balsam poplar.
Zone 3 contains Southern Canada and parts of Alaska. It also contains extreme upper areas of the United States including portions of Maine, Upstate New York, Vermont and Montana. Temperatures reach a low of minus 30 to minus 40 degrees in the winter. Nighttimes bring frost throughout the year and growing times are very short. Typical trees include balsam fir, Eastern hemlock, Eastern white pine and the Siberian crabapple.
Zone 4 contains many large bodies of water, such as the Great Lakes. The zone extends throughout the Northcentral United States, Wisconsin and Michigan. Successful trees include the sugar maple, green ash and Chinese juniper. Average winter temperatures reach minus 20 to minus 30 degrees.
The average low winter temperature in Zone 5 is minus 20 to minus 10 degrees F. It contains many ocean towns of New York and extends to Massachusetts, Northern Pennsylvania and Ohio, all the way to Newfoundland and Nova Scotia. Successful trees include the flowering dogwood, American elm, Eastern hemlock and the white poplar.
Zone 6 has a longer growing period. It contains the coastal towns of Massachusetts and moves through the middle portion of the United States and into parts of Arizona, New Mexico, Nevada and Washington. Successful trees include the Japanese maple, American chestnut and black walnut. Winter temperatures usually do not drop below minus 10 degrees.
The low winter temperatures in Zone 7 are zero to 10 degrees F. It covers an area that begins in Delaware and extends to the Southern United States into parts of Georgia, the southern tip of New Mexico and into California. Trees include crabapple, peach, pear and the big leaf maple.
Zone 8 contains the Western and Southern borders of the United States including North Carolina and across to the coast of Washington. There are four distinct seasons including a long growing season. Trees that thrive in this zone include the Arizona cypress, ginkgo and the Mexican orange. Low temperatures average around 10 to 20 degrees.
Zone 9 includes the extreme southern tip of the United States including portions of Florida, Louisiana and Texas. Temperatures rarely drop below 20 degrees. Summers are hot and tropical, while winters are mild. Successful trees include the California pepper tree, American elm and the flowering dogwood.
Zone 10 includes the Florida Keys, the central part of the island of Hawaii and portions of the California coast. This zone has little to no winter and rarely gets below 30 degrees. Popular trees in this area are the live oak, weeping willow and Catalina cherry.
Zone 11 includes the rest of Hawaii and the lowermost portion of the Florida Keys. Temperatures are 40 degrees and above throughout the year. The growing season is year-round and popular trees include the mango.