The term, 'perennial plant', means simply that the plant returns following severe freezes, to grow again the next year. Trees are cold hardy tested perennials by nature, some trees that are evergreens and do not go dormant, but merely slow down during various seasons, and other shade trees enter dormancy and shed the leaves. Tree growth of shade trees may stop altogether in extremely cold climates, but in the spring, will surge with buds that open to flower and leaf out.Great difficulties arise in assigning a plant, 'perennial', mainly because the primary determining factor, temperature range varies from year to year; and every century extreme cold temperatures may erase certain plant populations that have survived in areas before for decades or sometimes even centuries. A perennial plant may be a survivor, thus a "perennial" for a given growing area, then suddenly may become extinct in that growing area. The USDA has constructed a zone map that reveals averages of temperatures reached by the location in your State. This map is a nursery tool used to predict whether a perennial will live (cold hardy) in your area.Agaves are a diverse genus of over 200 species of rosette, spear-like, leafed evergreen perennials.
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