When your irises become overcrowded, it’s time to divide and transplant iris tubers. Generally, iris plants are divided every three to five years. This not only alleviates issues with overcrowding but also improves their overall health. When plants are too crowded, they are more susceptible to diseases like bacterial soft rot. In addition, plants are less likely to produce any blooms. Keep reading to learn more about replanting bearded irises.
When & How to Divide Bearded Irises
The best time to divide irises is during late summer, usually anytime between July and the first of September. Carefully dig up your iris clumps with a spade shovel and gently lift each clump from the soil. Shake off the soil and rinse each rhizome with water.
Trim the existing foliage into a neat fan about a third of their overall height, then use a sharp knife to cut or separate the rhizomes. In some cases, you may be able to just pull them apart. Make sure that each division or section contains a fan of leaves.
As you divide the rhizomes, take time to inspect them. Discard any that are old, leafless, soft, or rotting. Soft rot and iris borer are two of the most common causes for soft, mushy rhizomes in bearded irises. Replanting only the younger, healthier rhizomes will ensure the continual growth and vigor of your bearded iris plants.
Bearded Iris Transplant Instructions
Once you’ve ensured the health of your rhizomes through thorough inspection, you’re ready to transplant iris tubers. However, prior to transplanting irises, you’ll need to locate a similar area for replanting.
Bearded iris plants perform best in fertile, well-draining soil in areas with full sun. Their blooming is poor when given too much shade and poor draining can lead to bacterial soft rot.
Dig a hole large enough to accommodate at least three to five rhizomes. Mound the center with soil and place the rhizomes (with fans facing in one direction) on top, allowing the roots to sprawl over. Then fill in the hole and cover the rhizomes slightly—no more than an inch (2.5 cm.) or just below the soil surface. Planting too deep can also encourage rotting.
Replant additional rhizomes the same way, spacing each group at least 12 to 24 inches (31-61 cm.) apart. Water the irises thoroughly after transplanting. Newly planted irises should begin flowering within their second or third season.