Prune your plant in late winter or early spring. Remove about one-third of the oldest, thickest canes to encourage new, vigorous canes to develop. These new canes will decorate your landscape with splashes of red this fall and winter, because 1-year-old twigs have the intense fiery red color that gives redtwig dogwood (Cornus alba 'Sibirica') its name. If you continue to remove one-third of the oldest stems each year, your dogwood will always have brightly colored, vigorous shoots. Overgrown redtwig dogwoods can also be cut back completely to 6 inches above ground level. They will quickly send up new shoots.