Plant characteristics
This large shrub can easily obtain a height of 8-10 feet or more if not pruned regularly. Mother Nature throws us below-normal temperatures every few years, and when this happens, even the most protected butterfly bush will be killed to the ground. This is not much of a problem for most butterfly bushes, though, because they break, or come back up, easily from the root system and quickly regain in size.
The grayish-green leaves are simple and seem rather insignificant to the large and abundant flowers. The flower spikes are borne on new wood and can grow anywhere from 4 to 10 inches long. The first flowers of the season are the largest, and plants that go unpruned tend to have fewer but larger flowers than those that are pruned regularly.

Rainbow of colors
Flower colors of white, yellow, pink, rose, mauve, lavender, blue, purple, violet, and magenta are all commonly available. If they could come up with a good red I would be thrilled; for now magenta is as red as it gets and that's not red in my book. The flowers are pleasantly fragrant and bloom continually all summer, with the heaviest bloom period occurring from July to August and lighter flowering continuing until frost. Removing the spent blooms will promote more flowers late in the season. The flowers are quite attractive in a vase, but they don't last long once cut and shrivel in a day or so.
While it seems this vigorous plant will grow almost anywhere, it does require a site in full sun to bloom its best, preferring soil that is rich and well-drained. For the largest specimen just plant it and let it go in a spot that is at least 6 feet wide. I don't have that kind of room to spare in my garden, so I keep mine pruned to about 4 feet tall and about 3 feet wide. It still blooms profusely in the garden and is equally attractive to the butterflies.

Popular cultivars
There are so many cultivars of butterfly bush available today it's hard to choose just one. A few of the most popular are: 'Nanho Blue,' with small compact blue flowers; 'Nanho Purple,' with small compact purple flowers; 'Lochinch' has lavender flowers with an orange eye; 'Honeycomb,' a creamy yellow flower that is sweetly fragrant; 'Royal Red,' a plant that grows upright with purplish red flowers; 'White Bouquet' has white flowers with a yellow eye; and 'White Ball,' a new dwarf cultivar that is supposed to stay under 3 feet tall.
The hardiest of all butterfly bushes in our area is Buddleia alternafolia, alternate leaf butterfly bush. Unlike Buddleia davidii, this large cascading shrub flowers on old wood and only for 2-3 weeks. The soft lavender flowers are profuse, and the cultivar 'Argentia' has silvery foliage with purple flowers. This variety prefers a hot, sunny, and well-drained site and can grow easily to 10 or 12 feet, a very beautiful cascading shrub for any garden.