Even though there are plenty of newer colors than this old stand-by, I still find 'Petite Plum' to be my favorite. It is a very nice shaped 6 to 8 ft compact shrub, covered with deep lavender violet flowers all summer. Of all the butterfly bushes in our garden, it is the one most visited by butterflies and hummingbirds. With a little deadheading, I find it blooms from mid summer until November. It smells wonderful, and makes a nice cut flower.
Be sure to prune this plant heavily in early spring, down by at least 1/2 its size. Once established, it only needs occasional deep watering. It is a lovely specimen for a big container.