Buddleia davidii 'Nanho Blue' is a compact, arching butterfly bush grown for its long season of fragrant, purple-blue flower spikes and its strong pollinator appeal. You will get the best flowering and the densest habit in full sun, with good air flow and well-drained soil.
At maturity it typically reaches about 60-72 inches tall, with a broad, fountain-like spread. Flowers are produced on new growth, so you can prune in late winter to early spring to shape the plant and encourage fresh, floriferous stems through the season.
This shrub is generally hardy in USDA Zones 5-9. In colder areas it may die back after winter, but it often regrows vigorously from the crown once warm weather returns. Provide regular water while the plant establishes; afterward it can handle short dry spells better, especially in well-drained soils.
Use this selection where you want mid- to late-season color and a steady stream of visiting butterflies and other nectar-feeders. Deadheading can help keep the plant tidy, and prompt cleanup of spent blooms can reduce unwanted self-seeding in the garden.