Irises have rhizome roots that naturally multiply on their own. Typically, to grow or propagate irises, you plant rhizomes purchased from a nursery or from rhizomes that were divided for other rhizomes. However, if you still want to plant irises from seeds, it is in the realm of possibility for the average gardener, but it will take a lot of patience and perhaps a few failed attempts until success.
Gather the seeds, which are normally not available for purchase. You must collect the pods off the irises after they become plump in the spring.
Remove the seeds from their pods and soak them in warm water for 24 hours.
Sow the seeds in a flat planting tray in moist all-purpose potting soil, just below the surface. Put the tray in a black plastic bag and place it in the refrigerator for 3 weeks.
Dig a hole outdoors in an area that is shady and is large enough in which to set the tray inside. Move the planting tray outdoors and place it in the hole. Cover the tray with glass.
Keep the soil moist and wait for the irises to grow. It could take up to 18 months for the seeds to germinate. Do not transplant the irises to your garden until they have grown for at least 2 years (after germination).