Planting and Dividing Bearded Iris
by Don Janssen, Extension Educator
If you enjoy the spectacular orchid-like blooms of bearded iris, late summer or early fall is the time to add them to your perennials garden. This is also a good time to divide established iris that have become crowded.
Often the most difficult part about planting iris is selecting the varieties you want. The newest wrinkle in irises for the home garden is varieties that bloom in early summer and then bloom again later in the season.
Bearded iris get their name from the fuzzy, fringed structure that rests on each fall (the down turned petals; the upright petals are the standards). In some varieties, falls and standards are the same color; in others, they're different. The beards may be the same or a different color from the falls.
The main growing requirements of iris are full sun and good drainage. In poorly drained soil, root rot can be a problem. Iris should not be crowded by other plants -- weeds or other garden plants -- that overshadow them or mat closely around roots and foliage. Such crowding can promote the development of foliage diseases.
Till or spade the intended planting site a week or so before you intend to plant. Avoid incorporating barnyard manure -- it can promote root rot.
If the planting site is poorly drained, you can build raised beds to improve drainage or plant other types of iris that thrive in moist soil: Siberian iris (Iris siberica), butterfly iris (Iris spuria) or yellow flag (Iris pseudacorus).
Iris rhizomes are planted in shallow holes so that rhizomes are at or just below the soil surface. Irises planted too deeply may produce foliage but generally don't bloom. Irises are often planted in groups of four to six rhizomes spaced 12 to 15 inches apart. The advantage of close planting is a more striking display during bloom. A disadvantage is that clumps may have to be divided more often than every three to four years.
To divide crowded plants, carefully loosen the soil around the rhizomes and lift them from the soil. Cut off any soft, insect-infested or unhealthy-looking plant parts. Then use a sharp knife to divide the remaining rhizomes into pieces. Each piece for replanting should have some healthy-looking roots and at least one fan of leaves. Cut the leaves back to 6 to 9 inches before replanting the rhizome in a prepared site.
Bearded iris are divided into types by size. Dwarf bearded iris grow to 3 to 11 inches tall; intermediate ones reach 1 to 2 feet, and tall varieties grow to 2 to 4 feet. All bloom in early summer. The repeat bloomers flower in early summer and then again in late summer or early fall. All are hardy perennials with potential in beds, borders and foundation plantings.
The major insect problem of iris is the iris borer, a plump, pinkish caterpillar that enters the plant via the foliage. It moves down into the rhizome and feeds there. Insect-infested rhizomes are usually infected by a secondary rot that leaves them soft and mushy. The best way to control the borers is to remove iris foliage in the fall. Adults lay their eggs on foliage in late summer, so removing the foliage removes the eggs, too.
(This resource was added August 2004 and appeared in the Lincoln Journal Star Newspaper Sunday edition. For information on reproducing this article or using any photographs or graphics, read the Terms of Use statement)
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