Hardiness is most commonly understood as the ability of a plant to endure low temperatures. More appropriately, it should be considered as the ability of a plant to thrive in a variety of physical conditions. The U. S. Department of Agriculture's Plant Hardiness Zone Map provides a recommended range in which a plant will grow well. The map identifies eleven zones according to climate: the colder the winter temperature, the lower the zone number. Zone ratings are designed to indicate that a plant will not merely survive in a zone, but thrive. The zones are approximate, however, so some gardeners experiment with growing plants rated hardy for one zone north or one zone south of their location. Other factors - such as high temperatures, rainfall, altitude, soil and drainage, available light and air quality - should also be considered when choosing plants for your area.

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