Plant Black Adder Giant Hyssop in full sun with well-drained soil. Space plants 18-24 inches apart. Water regularly during the first growing season to establish a deep root system. Once established, it is drought-tolerant. Fertilize in early spring with a balanced fertilizer. Deadhead spent flowers to encourage continuous blooming. Cut back to the ground in late fall or early spring to promote new growth. Divide clumps every 3-4 years in spring to maintain vigor.