Perennial flowers are plants that live for more than two years. They are often used to differentiate a plant from shorter-lived annuals and biennials. Unlike short-lived annuals, perennials live for several years and require very little maintenance after initial planting. They die back every autumn and winter, and then return in the spring from their rootstock or other overwintering structure. Perennial plants can be short-lived (only a few years) or long-lived. They include a wide assortment of plant groups from non-flowering plants like ferns and liverworts to the highly diverse flowering plants like orchids, grasses, and woody plants. Perennial flowers are a great choice for gardeners who want long-lasting beauty and low-maintenance plants that return year after year. They mostly flower in spring, summer or autumn, with a handful blooming in winter, and many have attractive foliage, too. There are perennials to suit every type of garden, for any aspect or soil type, and they range in size from low-growing herbaceous plants for the front of a border, to medium-sized ones for the middle, to giants a couple of meters tall for the back. Some examples of perennial flowers include Black-eyed Susans, Monarda Didyma (Bee Balms), Mother of Thyme, Digitalis Dalmatian (Foxglove), Hellebores, Coneflower (Echinacea), Penstemon, and Asters.