Remove the old flowers of Vernonia lettermanii as they become brown and unattractive. Deadheading encourages the perennial plant to produce new flowers, keeping your plant looking attractive throughout the season. Deadheading also prevents Ironweed from spreading through your yard, as it can be an effective self-seeder when the dead flowers are allowed to dry completely and go to seed this would cause problems for your garden. Remove the brown stems and leaves to give your plant a healthier and more attractive appearance. Cut back Vernonia lettermanii to within 6 inches of the ground after it has finished flowering.