Wild Petunia (Ruellia humilis) is a seasonal plant with lavender flowers from summer into early fall. They prefer dry to mesic soil in sun to part sun where they grow up to 2 feet tall. They are a good choice for banks and slopes. Companion plants include Nodding Onion (Allium cernuum) and Prairie Dropseed (Sporobolus heterolepis).
No serious maintenance needs.