How to Propagate iris 'Thornbird'?
Propagate by division of rhizomes from midsummer to early autumn, see dividing irises

iris 'Thornbird' · Iris 'Thornbird'
Grow in well-drained, fertile, neutral to slightly acid loam in full sun. See bearded iris cultivation
Propagate by division of rhizomes from midsummer to early autumn, see dividing irises