Even though it is smaller than traditional buddleia, dwarf buddleia (also known as buddleja) still requires pruning to perform its best. Dwarf buddleias are a recent introduction to the world of butterfly bushes, and now that they are smaller, they can be enjoyed in even more locations. Most dwarf varieties grow about 90 cm (3 feet) tall and 90 cm (3 feet) wide, and they are a very useful addition to the perennial or mixed border. They grow best in full sun and well-drained soil.
Cut the stems to about 15 cm (6 inches) from the ground in early spring just when the new growth is beginning to show. After a cold winter, most or all of the stems will be dead at this time. However, even in warmer conditions, the plant benefits from being cut down each year.
Deadhead spent flowers as they occur. If you look closely down the stem, you will often see the beginning of a new flower bud forming. Cut just above that point. If you do not see a new flower bud, cut just above the point where the stem joins a lower stem. Deadheading encourages more blooming. It also prevents unwanted reseeding.
Cut the plant back in late autumn when it has completed flowering by about a third of its height. This is helpful if the budleia has got tall and you are in a windy location or if you are concerned about seeds forming. Otherwise, the plant can remain unpruned until spring.
Fertilise the plant in the spring with an application of a general fertiliser for flowering plants. Follow label directions.
The cultivar Blue Chip is a compact plant staying under 90 cm (3 feet) tall each season when pruned annually. It also has low seed set.