Buddleia davidii 'Black Knight'
(Butterfly bush, Summer lilac)
Butterfly bushes are carefree deciduous shrubs that are reliably fragrant and easy to grow. Butterflies swarm to their blooms all summer long. 'Black Knight' has deep purple-blue, almost black, flowers in elongated clusters on arching branches to 10 feet tall if not cut back, and half that size if cut back. The blooms come from early summer to first frost. The foliage is willow-like and grayish green.