The Best Time to Separate Iris Bulbs

Digging the Iris

• Trimming the plant's leaves is the first step to separating iris bulbs or rhizomes. Clip the leaves about 3 inches above the ground. Dig out the roots or bulb using a garden fork or shovel. Carefully remove the dirt from around the plant. Try not to disturb the small roots from the bottom of the bulb.

Separating the Iris

• Use any sharp knife to cut between the rhizome segments. Each segment should include a set of fine roots and some leaves. Dip the knife in a disinfectant mixture of 10 percent bleach and water between each cut to prevent the spread of disease between the iris plants. The bulb-type iris does not require cutting, but small bulbs around the base of the larger bulb can be separated.

Bulbs vs. Rhizomes

• Iris plants fall into to two broad groups. For example, Dutch iris plants form bulbs, while the bearded, Japanese and beardless Siberian irises form rhizomes. Rhizomes are horizontal root structures used for plant propagation, which also store nutrients for the dormant periods. Iris species with rhizomes are separated and moved in the late summer or early fall, while bulb iris plants are separated and moved in the late fall.

Planting the Separated Irises

• Start the new bulb or rhizome in a hole about 5 inches deep. Form a cone of soil that supports the rhizome or bulb, but allows the small roots to extend deeper into the soil. Backfill the soil around the roots, leaving the top portion of the rhizome exposed. Plant the newly separated iris bulbs or rhizomes about every 24 inches in the flower bed.