How to Prune Iris 'Lemon Tree'?
Remove any dying foliage in autumn, old flower stems can be cut down after flowering

Iris 'Lemon Tree' · Iris 'Lemon Tree'
Grow in well-drained, fertile, neutral to slightly acidic soil in full sun. Do not cover the rhizomes with mulch, or allow other plants to shade them; sun on the rhizomes encourages flowering. Give a high potash feed in spring and divide every three to four years. See also bearded iris cultivation
Remove any dying foliage in autumn, old flower stems can be cut down after flowering