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. Agave typically grows as low shrub-like plants in dry or well-drained soils of the Southern part of the U.S. from New Jersey down to Florida, and then West to California. Many Agave species, such as Agave americana or Agave tequilana, have sharp recurved, protective teeth running along both sides of the blade of its semi-curved, lance-shaped leaves, with a sharp needle-tip lance at the end. There are Agave species, like Agave attenuata, and Agave stricta, that do not have sharp-teeth at all, but are smooth. The color variations of Agave plants range from shades of green, to silvery-grey, bluish-green, top yellow or white stripes, such is the case with Agave americana 'media-picta'. The bloom of mother Agave plants are a beautiful array of pendulent bell-shaped, creamy-white flowers soaring high above the mother plant on a flower stem that may reach 20 feet or more for some agave species. The bloom period of a mother Agave plant is during the summer and the flower stalk is magnificent to behold, however, this event means the cycle of life ends for mother Agave and begins again for her Agave offspring. Agave plants are an excellent choice for rock gardens or well drained soils that lend themselves well to terracotta or cement planters. Agaves are fairly slow glowers so expect higher prices on these sunloving garden jewels at retail garden centers. Huge specimen agaves can be quickly delivered by semi-trucks.

The ancient Egyptians in 1500 BC grew the Aloe for healing, and while the Pharaoh held all the Jews in captivity, aloes were used as cosmetics and for the sacred healing power of this mysterious perennial. The Book of John, in the New Testament Bible, John 19-39, records that Jesus' body was wrapped in linen cloths and aloes after the corpse was removed from the crucifiction cross before burial. Aloes are evergreen perennial plants that grow as shub-like, climbing or tree-like plants. The aloe plant leaves are fleshly, succulent, long tongue-shaped groups of rosettes, or as star-patterned limbs. Most forms of the aloe, 300 species genus, have toothed leaf blades with soft to piercing hard teeth. Aloe saponaria and Aloe vera are the two most commonly found containerized aloes in homes and gardens. Aloe vera plant extracts have long been used by mothers on their children for fast relief for minor cuts and burns. Aloe saponaria is cold hardy down to freezing temperatures and is widely grown in Southern gardens for the beautiful, coral-colored, tubular blossoms and for the making of medicated soap. Most aloe plants are small, 1-3 foot tall and width, however, a few tropical aloe species, such as Aloe marlothii grow into large, 120 foot succulent trees. Aloe plant varieties may vary enormously in color from yellow, red to blue-greens, or to spotted or striped with random variegation.

Fern plants are a beautiful landscape choice or a container perennial, because of the delicate graceful foliage. Fern plants are native to the U.S., and found growing on every continent on the Earth. Some ferns grow well as cold hardy plants in some areas bordering arctic conditions. A gardener can find a fern perennial to buy in practically any nursery or mail order operation.

Florida tropical perennials are restricted for growing in many States, because of the lack of cold hardy resistance. Some gardeners prefer to plant Florida perennials in greenhouses, or to grow as an annual.

Flowering Vine perennials grow fast to cover fences, lattices, walls, and not only offer rewards of flowers, but many interesting flowers in colors of red, blue, white, pink, and yellow. If planted and grown in the sun, the flowering vines require little care of vine maintenance.

Yucca is a genus of evergreen plants, with approximately 40 species that grow in dry, desert-like areas. However, this is a common misconception, because members of the Yucca family can be found growing in 30 of the States in America, from New Jersey, down to Florida, and west to California. Yuccas can be grown as small shrubs or yucca trees, up to 30 feet tall, depending upon the yucca species. Yucca has lance-shaped leaves growing in a rosette pattern, on a woody stem or trunk-like frame. Yucca plants may vary dramatically in color from shades of green, to white or yellow stripes, to blue-green hues, as with Yucca rostrata, a jewel for any garden. Most yucca plants are stiff and sharp pointed, like the Spanish Bayonet (Yucca aloifolia), while some yuccas have flexable soft leaves, such as Golden Garland Yucca (Yucca flaccida). The flower blooms of yucca grow in summer, and develop into a beautiful, creamy-white pendulum of bell-shaped flowers that tower 8 feet above the mother plant. Yuccas are very adaptable and are among the oldest living trees in the world. The Joshua Tree (Yucca brevifolia), Yucca filimentosa (Bear Grass or Adam's Needle) is among the most cold-hardy and widely grown varieties. The strong, stringy filament (fiber), that run a course from the needle tip, down the margin of the leaf, was used by native Americans for making into garments and possibly the treating of war wounds.

The roots of Yucca were also used to make soap. The primary use for yucca plants in todays landscapes are for their ornamental beauty, like we find in Yucca flaccida 'Golden Sword', in terracotta pots or in ground landscape plantings. Some people use Yucca aloifolia 'Spanish Bayonet', Yucca treculeana 'Spanish Dagger', or even Yucca brevifolia 'Joshua Tree', as security hedges for their beautiful and exotically bazaar, stiff leaves, hence the nickname, "Burlars' Nightmare." Yucca plants are typicall sunlovers, growing in well drained soils, but are adaptive and often grow faster in moderately moist areas, such as the Southeastern U.S.