Blue flag iris can be propagated by division or by seed

Division

1. Prepare Sanitize tools and trim the foliage to about half its height. 

2. Dig Gently lift the plant with a fork, being careful not to damage the rhizomes. 

3. Separate Cut the rhizomes into sections with a sharp knife, making sure each section has at least one growth point. 

4. Replant Dig holes in nutrient-rich, well-draining soil and space the rhizomes about two feet apart. 

5. Water Water the newly planted irises generously and keep the soil moist but not waterlogged. 

Seed propagation 

  1. Harvest: Collect seeds in late summer.
  2. Stratify: Place the seeds in a moist medium and refrigerate for a few weeks.
  3. Plant: Sow the seeds in shallow containers in a well-drained growing medium.
  4. Maintain: Keep the soil consistently moist and maintain a cool temperature range.
  5. Transplant: When the seedlings are sturdy enough, transplant them to their permanent location.

Late summer or early autumn is the best time to divide blue flag irises. Dividing at this time allows the plants to become well-established and reserve carbohydrates, which increases the likelihood of flowering the following spring.