A perennial plant is a plant that lives for more than two years. When used by gardeners or horticulturalists, this term applies specifically to perennial herbaceous plants. Scientifically, woody plants like shrubs and trees are also perennial in their habit.
Perennials, especially small flowering plants, grow and bloom over the spring and summer and then die back every autumn and winter, then return in the spring from their root-stock rather than seeding themselves as an annual plant does. These are known as herbaceous perennials. In Marin’s climate, many perennials do not die back to the ground in the winter but do look better when last year’s growth is trimmed back in early spring. (Courtesy of Wikipedia)
See a preview of Perennials.