This is the popular and pretty purple variety called 'Dark Knight'.
'Pink Perfection' is a robust grower with grayish-green foliage.
Butterfly bush is a deciduous to semi-evergreen shrub with a weeping form that can get 6-12 ft (1.8-3.7 m) tall and have a spread of 4-15 ft (1.2-4.6 m). Butterfly bushes have opposite, 6-10 in (15-25 cm), lance-shaped gray-green leaves on long arching stems. The tiny flowers are irresistible to butterflies. They are borne in long, 8-18 in (20-45.7 cm), cone-shaped clusters that droop in a profusion of color and stay abuzz with winged, nectar-feeding insects from late spring until first frost in autumn. The flower clusters can be so profuse that they cause the branches to arch even more. The flowers of many cultivars are sweetly fragrant. Flower colors may be purple, white, pink, or red, and they usually have an orange throat in the center. There are a great many named selections to choose from. 'African Queen' has dark purple flowers. 'Nanho Blue' or 'Petite Indigo' is compact and smaller, to 5 ft (1.5 m) tall and has 6 in (15 cm) clusters of blue-lavender flowers. 'Nanho Purple' and 'Nanho White' are also compact bushes. 'Royal Red' has flowers of dark reddish purple. 'White Bouquet' has white flowers with orange throats. 'Opera' has pink flowers in clusters to 2 ft (0.6 m) long.
Location Buddleja davidii, the butterfly bush, is native to northwestern China and Japan.
Butterfly bush likes well drained, average soil. They thrive in fairly dry conditions
once established. Roots may perish in wet soil. Butterfly bushes are semi-evergreen in climates with mild winters. They may be cut back to the ground and will re-emerge from roots in their northernmost range, but will not reach the maximum size they do in warmer climes. It is advisable to cut back the shrubs in any case, since flowers are usually larger and more prolific on new wood. Avoid the use of insecticides around buddleias. Pinch off spent flower clusters to prolong blooming. Light: Plant butterfly bush in full sun to part sun. Moisture: Average to dry. Hardiness: USDA Zones 5-10. Butterfly bush will die to the ground in winter in zones 5 and 6 but it comes back in spring. Propagation: Butterfly bush is very easy to root from cuttings in warm weather.
Having one of these in the butterfly garden is almost essential as it blooms a lot over a long period and is a delicious dining destination for hungry butterflies!
Butterfly bush is the perfect foundation plant for a butterfly garden. The larger cultivars should be placed behind other shrubs and blooming annuals and perennials. Dark flowered varieties show up quite well against a light background. Plant alongside pentas (Pentas lanceolata), lantana
(Lantana camara) and zinnias Zinnia elegans) for non-stop butterfly activity, and find a place nearby for parsley (Petroselinum crispum), passion vine (Passiflora incarnata) and other butterfly larval food plants. See Floridata's Butterfly Gallery for more ideas.
You are likely to see this genus referred to as Buddleia davidii in some horticultural publications but Buddleja davidii is the correct botanical name. In addition this genus, formerly assigned to the family Loganiaceae has been split out into its own family called Buddlejaceae. We still like to use buddliea as a common name for butterfly bush - read What's In a (Plant) Name for more on botanical nomenclature.
Butterfly bush is one of the most attractive plants to butterflies; the white varieties may be most attractive of all. The fragrant flowers, gray-green leaves and constant motion of winged insects are a delight in any landscape. Butterfly bush is a fast-growing shrub that requires little care. No garden should be without this beauty - but see warning below!.
WARNING Butterfly bush has become an invasive pest in some climates. Check locally to determine that buddliea is not a problem species in your area before planting.