A map of plant zones is available at the U.S. Department of Agriculture's Agricultural Research Service site. The zones also are known as USDA hardiness zones. The site offers a color-coded map showing all U.S. zones, and it allows users to input their zip codes to find their specific zones.
The United States is broken down into 13 large zones that are divided according to the average annual coldest temperatures for each area, as of 2015. There is a 10-degree Fahrenheit difference between each zone. Learning the zone number for a particular area provides gardeners with valuable information about when and what to plant.