Q. When and how do I divide irises?

A. The best time to plant and transplant rhizomatous (or self-seeding) iris is after flowering but before the end of August. Established plantings of iris should be divided every three to four years or when the clump becomes crowded and flowering decreases. When transplanting iris, first cut back the leaves to approximately 1/3 of their height. You can lift the entire clump with a spade or digging fork and use a sharp knife to separate the rhizomes. Proper sanitation is important to reduce the spread of disease, so dip the knife in 10 percent bleach to water solution after each cut. Remove and discard old rhizomes and replant the younger, smaller rhizomes. The newly transplanted rhizomes should be firm and should have roots and a fan of leaves.

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