The term “perennial plants” refers to a large number of plants that live longer than two years. Perennials include trees, bushes, shrubs, flowers, grasses, and weeds. When they are planted within their hardiness zone, they are easy to grow and often require little care.

TYPES OF PERENNIALS
There are five types of perennial plants.  Deciduous perennials are one type.  In this group of perennials, the leaves fall off during the colder months.  A couple of examples are the goldenrods and mint.  A second type is the evergreen perennial.  They keep their foliage year round.  Bananas and begonias are a couple of examples of evergreen perennials. Woody perennials are a third type.  These plants include maple trees, pine trees, apple trees, pear trees, and many forest plants.

Another type of perennial is herbaceous plant.  In their native climate, these plants die back to the roots every year, usually during the winter.  Then they grow back from the roots the following spring.  Examples of these are alfalfa and red clover.

The final type of perennial plant is the monocarpic perennial.  This perennial can live a few years or many years.  An agave plant is one example.  Monocarpic perennials will bloom once then die.  However, monocarpic perennials will produce new plants at their base before perishing.

BENEFITS
Perennial plants over all are quite hardy, and have several benefits.  For instance, some perennial plants can survive in the extreme cold.  Herbaceous perennials can survive wildfires.  The roots of perennials can help prevent erosion.  Perennial plants also help increase the quality of the earth's air, and slow down global warming.

More benefits are listed in the article "Perennial Crops: Plant Once, Harvest Many Times"