The word iris means "rainbow". True to that, iris bulbs produce a rainbow of colorful flowers on tall stalks that are excellent for cutting and enjoying in a vase indoors as well as in your garden along a fence as a background planting. There are over 200 varieties of iris. Irises spread by sending out stems underground. These are the rhizomes that you can cut apart and plant separately to create additional plants in your garden and share with others. When your iris bed gets crowded with plants, it is time to separate them.
Divide iris plants in August or September after they finish blooming. Loosen the soil around a clump of plants with a shovel or fork and separate the rhizomes with a sharp knife.
Trim the roots and remove any diseased or unhealthy-looking areas from each separated rhizome.
Cut back the top leaves to 4-6 inches, leaving green growth to feed the new plant for future blooms.
Prepare a shallow planting hole for each plant. Plant the individual rhizomes in holes 8 inches apart. Cover them with loose soil just to the base of the rhizome.
Water the new plants and place a shallow covering of mulch on top, being careful not to cover the base of the rhizome. They will establish roots and produce foliage and maybe flowers in the spring. It may take another year for the new iris plants to bloom.