History

• Flowering cherries are hardy to Zone 5, and can survive to minus 20 degrees.sakura flowering image by Petro Feketa from Fotolia.com
  
  The United States Department of Agriculture in conjunction with The U.S. National Arboretum and The American Horticultural Society collected the coldest annual temperatures from more than 14,500 stations across the United States, Canada and Mexico over a period of 10 years. The average lowest temperature was recorded by latitude and longitude, and the Plant Hardiness Zone Map was created.
  
  

What the Numbers Represent

• Bottle brush shrubs are hardy to Zone 8.bottle brush image by Wendy Hotalling from Fotolia.com
  
  The numbers 1 to 11 represent a temperature range of 10 degrees Fahrenheit. The number 1 represents the coldest places in North America with an annual lowest temperature colder than 50 degrees below zero, and the number 11 representing the warmest regions with an annual coldest temperature above 40 F.
  
  Each number between 1 and 11 represents 10 degrees. Zone 2 is minus 50 F to minus 40 F and so forth. The map is further broken down into "a" and "b" sections which symbolize 5 degree changes. Zone 2a is minus 50 F to minus 45 F and Zone 2b is minus 45 F to minus 40 F.
  
  

Choosing Your Plants by the Map

• Every plant is assigned a zone number that correlates with the USDA Plant Hardiness Zone Map. When choosing a plant for your garden, make sure to pick plants that are hardy in your zone or lower. For example, if you buy a Japanese maple that is marked as a Zone 5, if you live in a Zone 5 that plant will survive the winter. If your live in Zones 1 to 4, that plant will most likely have winter damage or die. If you live in Zone 6 to 11, you will not need to worry about it surviving the winter. Always choose plants that are at or below your plant zone.
  
  

Other Factors

• Using the USDA Plant Hardiness Zone Map should only be a guideline for choosing your plants. There are many other climatic factors that can increase or decrease a plant's ability to survive in a certain environment. Every yard contains micro climates, small areas that have different climates from the areas surrounding it. These differences can be warmer or cooler, wetter or drier, humid or windy.
  
  Many artificial environments (such as container planting) take a plant's roots away from the warming influence of soil, thereby influencing the effectiveness of choosing a plant only by its zone number. Remember these other factors when you choose your plants.