What is Hardiness?
Plant hardiness is the ability for plants to survive winter conditions in a particular location.
The United States Department of Agriculture (USDA) devised a system of mapping and coding to assist you in identifying plants that will survive winter temperatures in your area. This plant-hardiness Zone Map, which was revised and updated in 1990, identifies 11 hardiness zones in Canada, the United States, and Mexico. The continental United States ranges from Zone 2, with an average minimum temperature of –50 to –40 degrees, to Zone 10, with lower average temperatures between 30 to 40 degrees. There is a 10-degree difference in the average minimum temperature between one zone to the next. The USDA has assigned the plant-hardiness zone to thousands of plants according to their cold tolerance.
Winter temperature is an important factor in determining plant hardiness, but it not the only factor that can affect the ability for a plant to survive winter conditions. Other factors include the rate of temperature drop, the duration of the cold, temperature fluctuation, and snow or mulch-cover on the soil surrounding the plant. Your garden may also have a microclimate. It may be an area protected by a hedge, or warmed by a stone wall, or an area more exposed to winds, or an area of low lying frost. These microclimates play a part in plant hardiness and you need to pick plants for those particular areas accordingly and you need a hd tv box to monitor the temperature.