Size of Bearded Iris Bulbs

No Bulb

• The bearded iris does not grow from a bulb, so there is need to worry about its size when planting. A bearded iris grows from a tan rhizome that stores the plant's nutrients. Rhizomes are swollen stems that grow horizontally just under the soil's surface. The University of Minnesota Extension states that rhizomes send roots downward, while shoots with sword-shaped leaves grow upward. These leaves eventually fan out, revealing a flower stem or scape that grows flowers.

Planting

• Plant bearded irises in July and August. They grow best in well-draining, fertile soil in a location receiving full sun. Amend soil with organic matter such as compost, aged manure or peat. Plant so the depth of soil barely covers the rhizomes, no more than 1 inch. If planted too deeply, bearded irises produce leaves without blooms and are more likely to become diseased. Fertilize the plant every spring.

Division

• Colorado State University Cooperative Extension recommends dividing and replanting bearded irises every 2 to 4 years. Otherwise, they become overcrowded clumps, and roots no longer receive air and sun. Use a sharp knife to trim younger rhizomes from clumps into sections that include healthy roots and one or two strong leaf fans. Discard old rhizomes.