Louisiana irises can be propagated by dividing the rhizomes or by planting seeds.
Rhizome division
Identify healthy rhizomes: Look for firm, plump rhizomes with healthy roots.
Divide the rhizomes: In the fall, dig up the irises and break off the new plants from the old rhizomes.
Replant the divisions: Place the divisions in a bed or container, making sure the top of the rhizome is about half an inch below the soil.
Water and mulch: Water the bed thoroughly and add a 2-inch layer of mulch.
Seed propagation
Harvest the seeds: When the pods are yellow and cracked, harvest the seeds.
Plant the seeds: Lightly score the pod and remove the seeds. Plant the seeds in a pot with potting soil, and cover with about ¾ inch of soil.
Water and place in a shady location: Keep the soil moist but not soggy.
Monitor the seeds: Push down any seeds that pop up to the surface.
Transplant the seedlings: In late January or early February, transplant the seedlings into a garden bed.
Additional tips
Divide irises during their dormant season in early spring or late fall.
Improve the soil with organic matter and fertilizer. Louisiana irises prefer acidic soil with a pH of 6.5 or lower.
Dividing irises encourages new growth and increases their bloom capacity.