It may be a small contribution to ornamental horticulture, but I have a theory that if the edges of your perennial borders are crisp and attractive, you are well on the way to a satisfying garden. Well-clad edges create a favorable first impression, reassure garden viewers that all is right with the world, and hide a multitude of sins by diverting attention from weeds or other flaws in the background. Think of edges as lines that delineate shapes and, and the same time, define adjoining spaces.
Edges create order.
They set apart the man-made from the wild and divide space within a garden. They also frame pictures, direct the eye, and provide unity. From a design point of view, they even determine style. The key to an effective edge for your perennial border is suitable plant material. Finding perennials that fulfill the many obligations of an edging plant is a challenge.