Some areas are considered too high in elevation for plant cultivation and so are not assigned to any zone. Many large urban areas are in a warmer zone than the surrounding land.
Plants grow best within an optimum range of temperatures.
The range may be wide for some species, narrow for others. Plants also differ in their ability to survive frost and their sun or shade requirements. The zone ratings indicate conditions where designated plants will grow well, and not merely survive. Refer to the map to find out which zone you are in. In the herbals shown on the Nutritional Focus web page you will find recommendations for the plants that grow best in your zone.