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Bearded Irises prefer alkaline, well-drained, sandy soil making them excellent candidates for hillsides or rock gardens.

They grow from swollen roots called rhizomes that must remain near the soil surface when planted. Take a soil test and amend with rock phosphate and/or greensand mineral powders if phosphorus or potassium are low. Plant in clusters of at least 3 roots spaced 2" apart with the rhizomes pointing away from the center.

Bearded Irises have blue green foliage that remains attractive in the spring and offers an upright, sword like design element in the perennial garden. Growth of the leaves stops in late June and the foliage often starts to decline in July. Clean the crowns of any brown, yellow, or dead leaves and make sure the rhizome is “sunbathing” on the soil surface. If needed, cut the foliage down to about 2-3”. Don’t worry, they will start growing again in late summer and into the fall.

Bearded Irises should be divided every 3-5 years to keep the clumps vigorous, avoid rhizome deterioration in the center, provide maximum bloom, and help to control the Iris borer, their most common pest. The life cycle of the Iris borer is as follows:

Eggs for the Iris borer larvae are laid on leaves by moths in late fall. The caterpillars emerge in early spring, pierce the foliage, and enter the leaves. They tunnel down (leaving linear tracks) and enter the rhizomes, growing to be fat, flesh-colored worms 1½-2" long. They eat out the center of the rhizomes then migrate into the soil, where they pupate. In late summer and fall they turn into night-flying moths that are purplish yellow in color. The moths lay eggs on the Iris foliage and debris at the base of the leaves. The eggs are a creamy green, later turning lavender. The most important control measure is GARDEN SANITATION! Cut and eliminate all stalks and foliage each fall, as they are the primary over wintering site. Do this late into the fall, shaving the foliage as close to the rhizomes as possible. In early spring, if you see borer tunnels starting in the leaves, pinch them to kill the larvae.

Bearded Irises, unlike most perennials, are divided in July and August when they have ceased their active growth cycle. Dig up the clumps, separate them (they come apart easily by hand prying). Remove the outer, healthy "fans" of foliage each with a 2" long rhizome attached. Cut off the older rhizomes, being sure to remove all soft rot or borer-damaged rhizomes. You will get a surprising number of divisions from each clump! Reset rhizomes just at the surface of the soil in clusters of 3-5 fans facing away from the center, set 2" apart. They will bloom lightly the first year and beautifully the second year. You should complete this project by mid-September to allow the rhizomes to put down good roots for the winter. Never use mulch over the rhizomes, but it is a good idea to apply a loose covering of evergreen boughs over your newly replanted Iris patch in late fall as soon as the ground has frozen. This prevents heaving of the roots in the winter.

For large, established Bearded Iris patches, time your division to do 1/3 of the patch each year. This will ensure that flowering will always be abundant, and the clump will retain its vigor.

Many of our modern Bearded Irises are classified as reblooming. These plants bloom at the normal time in the late spring/early summer and then repeat bloom in the fall.

 

In an effort to provide horticultural information, these educational documents are written by Nancy DuBrule-Clemente and are the property of Natureworks Horticultural Services, LLC.  You are granted permission to print/photocopy this educational information free of charge as long as you clearly show that these are Natureworks documents.