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. Nearly black flowers. Attractive to butterflies, hummingbirds, and bees. Easy to grow, but is in invasive in some areas. Fast grower. Easy to grow in fertile, well-drained soil in full sun. Prune back or cut to the ground in late winter or early spring. Deadhead regularly.