Bluebeard 'Dark Knight' is a small flowering shrub grown for its deep blue-purple flower clusters, which arrive in summer when little else in that color is blooming. The gray-green, lightly aromatic foliage stays tidy on a rounded plant 2 to 3 feet tall and wide, and bees and butterflies work it constantly.

Give it full sun and well-drained soil; soggy ground in winter is what sets it back, not cold. Cut it back hard in early spring, since it blooms on new wood, and it regrows into a fresh, compact mound. Deer and rabbits leave it alone.