The best time to plant and divide Louisiana Iris is mid-to-late August and September. Transplanting immediately after blooming is not recommended. If existing beds are to be divided and replanted, dig out all the Iris and rework the beds, adding organic materials and a commercial fertilizer. Replant as soon as possible, preferably the same day. Do not allow the newly planted beds to dry out; water every few days until the plants are established. Planted in a triangular format (about 12 inches apart), they can be left 3 to 4 years and will form nice clumps.
Iris grow in the direction they face; at least two offsets generally form each year, one on each side of the rhizome. Each rhizome blooms only once, then the offsets bloom the next year. Good growth and offset formation are, therefore, necessary each season for consistent bloom. The offsets represent vegetative reproduction and are identical in every respect to the parent rhizome.
~The above culture information adapted from The Society for Louisiana Iris website