A perennial is a plant that lives for more than two years. Perennials are hardier than annuals and generally considered the foundation of your garden. They come in a variety of shapes, sizes and colors and some varieties provide year-round foliage. Evergreen perennials will keep their foliage through winter, providing color as it changes with the seasons. Other perennials are herbaceous, which grow and bloom during the spring and summer months and then begin to die back in the autumn and winter months returning again in the spring.