How to Prune tall bearded iris 'Tall Chief'?
Cut down old flower stems after flowering, and remove any dying foliage in autumn

tall bearded iris 'Tall Chief' · Iris 'Tall Chief'
Plant in full sun in well-drained soil, and with the top surfaces of the rhizomes exposed so that they get baked in summer sun, which encourages flowering. See bearded iris cultivation
Cut down old flower stems after flowering, and remove any dying foliage in autumn