Perennials are herbaceous plants. In winter their tops die back, while the crown and root systems go dormant. The following spring the tops reappear and roots come out of dormancy. When grown from seed, they produce vegetative growth the first year and bloom the second. With proper care they will continue to add color and foliage interest to the garden for many years.
Most plants grown from bulbs are also perennials, but are usually thought of as a separate category of plants, since their needs and care may be different. Ornamental grasses, too, are usually perennial plants. Technically, shrubs are perennials, too but because of their woody stems, they are not herbaceous perennials.
Information adapted from: http://gardening.cals.cornell.edu/
Last updated June 10, 2019