Tall Bellflower (Campanula americana) is a seasonal interest plant with blue flowers from mid-summer to early fall. They prefer moist to mesic soil in part sun to shade where they can grow between 2 and 6 feet tall. They are a good choice for shaded slopes. Companion plants include Lady Fern (Athyrium filix-femina) and Woodland Phlox (Phlox divaricata).
Taller plants may need to be staked while in bloom if not supported by other surrounding plants. If needed aesthetically, stems can be cut back to the ground. Deadheading will prevent plants from spreading.