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When to Divide Bearded Iris |
By James E. Klett, Colorado State University Cooperative Extension Specialist, Landscape Plants
Clumps of bearded irises should be divided and replanted before they become overcrowded, generally every two to four years.
A single rhizome will branch many times over the years, developing into a heavy crisscross clump, often choked with old leafless rhizomes. If it is not divided, the mass of leaves will exclude sun and air from the roots. This will lead to poor flowering or no flowering and often weakens the plants making them more susceptible to insects and diseases.
Dividing of irises is best done now, in August, which is the same time of year that plantings should be made. Lift each clump by gently prying it loose from the soil. A spading fork is better for this than a shovel because it is less likely to cut roots and rhizomes.
Use a sharp, strong?bladed knife to trim younger rhizomes into sections that include healthy?looking roots and one or two strong leaf fans. Under low pressure from a hose, carefully wash soil off roots. Discard old rhizomes from center sections.
Trim existing leaves to a neat fan shape and then dig a hole to replant, so that the rhizome will be set no deeper than one inch. Check to be sure that all leaf fans face the same way, then spread roots out evenly. Firm the soil around the rhizome to eliminate major air pockets in the soil.
Photograph courtesy of Judy Sedbrook.
