Will your plant flourish? Climate growing zone maps were created as a tool to help gardeners grow and propagate a successful garden. Climate zones are used as a guideline to determine the hardiness and survivability of various plants and trees in a geographic area. Making your plant selection will be easier by knowing the growing zone for your location. When I mention hardiness I mean winter hardiness zone; determined by the plant’s ability to survive over the winter which is critical to the plants adaption to its environment.
For example, you would not want to put something in your garden that cannot handle hotter temperatures if you are located in one of the warmer climate zones. Conversely, if you live in a very cold zone, it would not make sense to try to plant something in your garden that is suited for a hotter climate. If you want a shrub, perennial, or tree to survive and grow year after year, the plant must tolerate year-round conditions in your area, such as the lowest and highest temperatures and the amount and distribution of rainfall.
Today, the USDA map is the standard measure of plant hardiness throughout most of the U.S. The climate zones are based on the average annual minimum winter temperature, divided into 10-degree F zones. Plants differ in their ability to survive frost, and their responses vary from immediate death to sustained performance. A plant’s placement within the landscape, how they are planted and their overall size and health greatly influences a plant’s satisfactory adaptability. Every gardening zone has temperature differences, differing amounts of daily sunlight and rainfall. pH is the measure of acidity or alkalinity of the soil. The ability of a plant’s roots to take up water and nutrients is dependent up the pH of the soil. All plants require a medium pH in the range of 10 to 14 to keep essential nutrients in balance. All of these components affect a plant’s ability to thrive in its environment.
The USDA divides North America into 11 hardiness zones, each of which represents an area of winter plant hardiness. Zone 1 is the coldest, found in Canada and the far northern U.S.; zone 11 is the warmest, a tropical area that is essentially frost-free and found only in Hawaii and southernmost Florida. The temperatures listed indicate the average annual minimum temperatures — the lowest temperatures that can be expected each year.
USDA Hardiness Planting Climate Gardening Growing Zones and average annual minimum temperature
- Climate Hardiness Growing Zone 1
- Below -50 F (-45.6 C) , example city – Fairbanks, Alaska
- Climate Hardiness Growing Zone 2
- -50 to -40 F (-45.6 to -40 C) , example city – Prudhoe Bay, Alaska
- Climate Hardiness Growing Zone 3
- -40 to -30 F (-40 to -34.5 C) , example city – Tomahawk, Wisconsin
- Climate Hardiness Growing Zone 4
- -30 to -20 F (-43.5 to -28.9 C) , example city – Northwood, Iowa
- Climate Hardiness Growing Zone 5
- -20 to -10 F (-28.9 to -23.3 C) , example city – Mansfield, Pennsylvania
- Climate Hardiness Growing Zone 6
- -10 to 0 F (-23.3 to -17.8 C) , example city – St. Louis, Missouri
- Climate Hardiness Growing Zone 7
- 0 to 10 F (-17.8 to -12.3 C) , example city – Griffin, Georgia
- Climate Hardiness Growing Zone 8
- 10 to 20 F (-12.3 to -6.6 C) , example city – Austin, Texas
- Climate Hardiness Growing Zone 9
- 20 to 30 F (-6.6 to -1.1 C) , example city – Phoenix and Tucson, Arizona
- Climate Hardiness Growing Zone 10
- 30 to 40 F (-1.1 to 4.4 C) , example city – Miami, Florida
- Climate Hardiness Growing Zone 11
- 40 F and above (4 C and above) , example city – Honolulu, Hawaii – Mazatlan, Mexico
Growing Zones USDA Hardiness Zone Map has its flaws.
Some flaws of the climate zones in the West are the many factors beside winter lows, such as elevation and precipitation. In the West, weather comes in from the Pacific Ocean and gradually becomes less humid and drier as it moves over and around the mountain ranges. For example, the weather and plants in low elevation, coastal Seattle are much different than in high elevation, inland Tucson, Arizona, even though they are in the same growing zone 8.
TIDBIT: The USDA Hardiness Zone map was developed under the direction of Henry T. Skinner, the second director of the U.S. National Arboretum. Mr. Skinner worked in cooperation with the American Horticultural Society and horticultural scientist throughout the United States to incorporate pertinent horticultural and meteorological information into the map.