Good article. No absolutes about when to prune. Can take place any time of the year, but should take place during winter months, while plant is dormant. Cut back entire shrub to within a foot or two from ground. Cut back, trim during spring, or even summer: these shrubs can handle stress well and will come back stronger than ever. Bushes grow quickly and respond well to pruning. New growth and blooms should reappear within weeks of pruning.
Buddleja davidii blooms in purple, pink, or white with lightly fragrant flowers. Because it blooms on new wood, you can trim it to the ground in late winter to keep plants more compact. 'Blue Chip' butterfly bush grows only 20 inches tall and wide and blooms continuously from early summer through autumn. Full sun and well-drained soil. Learn more about butterfly bush.