How to Propagate Iris 'Immortality'?
Propagate by division of the rhizome shortly from mid-summer to early autumn. See dividing irises

Iris 'Immortality' · Iris 'Immortality'
Grow in any moist but not waterlogged, neutral to slightly acidic soil in full sun. Plant in late summer or early autumn. In drier soils, dig in well-rotted manure before planting. See bearded iris cultivation for further advice
Propagate by division of the rhizome shortly from mid-summer to early autumn. See dividing irises