A perennial is any plant that produces seeds and flowers more than once, enabling it to live for more than one year. Perennials include shrubs and trees, as well as flowers that grow and bloom in the spring and summer only to die in the autumn and go dormant in the winter. Perennials maintain their growth through bulbs, roots, horizontal stems that spread underground, and tubers of one sort or another.
A perennial grows from a root stock. Annuals, which live for one season, and biennials, which live for two seasons, grow each spring from seed. Perennials, especially those in the wild ordinarily have large root systems capable of retrieving soil nutrients and water from deep in the soil.
An herbaceous perennial (that includes most flowers) does not form permanent woody tissue. In warm climates, herbaceous perennials are evergreen, retaining their foliage all year round. In climates with seasons, they become deciduous, losing their leaves in the fall. They go dormant in the winter and retain their leaves in the spring.
The same perennial can be evergreen or deciduous depending on the growing zone. If they are growing in the south, they retain their foliage all year. If they grow in the north, they drop their leaves in the fall and go dormant during the winter.
Some herbaceous daisies include geraniums, begonias and irises, among numerous varieties of flowers.
Woody perennials include all shrubs and trees. Like herbaceous perennials, they too can be evergreen or deciduous, depending on the climate. Those trees with needles, including pines, spruces, junipers, cedar and firs, are evergreen. Those perennials with broad leaves that drop in the fall are deciduous. These include oaks, maples, birch, larch, aspen and other trees.
Growing Herbaceous Perennials
While perennial flowers keep coming back year after year, it might not bloom the first year after it is planted. Most perennials have short blooming periods, from one to three weeks each year. Some plants need to be replaced every three to five years.
Perennials are popular among gardeners because they are generally hardier than annuals and require less care and maintenance. Some gardeners in cold climates treat a plant that is perennial in a mild climate as if it were an annual. They plant it each year from a cutting, by dividing it or from seed.
While herbaceous perennials live only a few years, woody perennials can live for centuries. The Methuselah tree, a great basin bristle cone pine (Pnus longaeva) in the White Mountains of California, is more than 4,000 years old. The Japanese say that a cedar in Yakushima, Japan, is more than 7,000 years old.