What does Zone mean?
A zone is a region used to classify plant hardiness by various climates. An appropriate climate for specific plants is essential for optimum plant growth and yield. The zones depicted on a zone map help provide accurate information to determine a plant’s suitability for a given location.
The United States Department of Agriculture (USDA) plant hardiness zone map is the de facto standard that gardeners rely on to determine the hardiness of plants within their growing zone.
More Info On Zone
Gardeners need to know which plants will grow best in their climate; the USDA Zone Map provides that information. When a gardener is selecting seeds or plants for their garden, most often they are labeled for plant hardiness according to the USDA Zone Map.
The zone map separates the US into 11 distinct growing zones with each zone being 10 degrees warmer (or colder) than the previous. In some cases the zone is broken down even further with an “a” or “b” region within it.
The modern 2012 zone map is based upon average temperatures during the 30-year period of 1976-2005 and is more accurate than the 1990 version which was based upon data from only a 13 year period.
The algorithms of the map consider such factors as terrain, elevation, nearness to large bodies of water, and position of the terrain. Valley bottoms, for example, are much cooler than the ridge tops that receive much more sunlight.
This definition was written in the context of Horticulture