One of my favorite plants for attracting butterflies is Verbena bonariensis. It grows 3 to 4 feet tall and prefers full sun but will tolerate some light shade.
Verbena bonariensis is considered a perennial in zones 7-9, but I grow it as an annual in my Zone 5 garden. The flowers appear on tall, airy stems that are almost see-through. Because of this, you can plant them anywhere in the border—even in the front. The flowers hover over all the other plants.
Verbena bonariensis self-seeds and can be considered invasive in warmer areas, but I don’t have a problem with it. Once in awhile I get a few volunteers, but they are always welcome. The fragrant flowers are covered with butterflies and bees all summer long.
While the plants have no pest problems, I must confess that they usually develop powdery mildew by late summer. Fortunately, it doesn’t affect the flowers.