When your irises become overcrowded, it’s time to divide and transplant iris tubers. Generally, iris plants are divided every 35 years. For information on how to divide and transplant correcting, read this article.
Plant your rhizomes at or just barely below the surface of the ground. Bearded Irises should be planted so the tops of the rhizomes are visible and the roots are spread out facing downwards in the soil. However, in extremely hot climates or with very light soils, cover rhizomes with up to one inch of soil.