 | Most gardeners are familiar with the U.S. Department of Agriculture's Cold Hardiness Zone Map. First published in 1960 and updated in 1990, this map is based on average annual minimum temperatures recorded throughout North America. By using the map to find the zone in which you live, you can determine which plants will "winter over" in your garden because they can withstand these average minimum temperatures.
Although these zones are useful as an indictor of a plant's likelihood for survival in a given area, many factors, including soil type and fertility, soil moisture and drainage, humidity, and exposure to sun and wind determine a plant's growth and success or failure in its environment. Today, nearly all American reference books, nursery catalogs, and gardening magazines describe plants using USDA hardiness zones. | |