Master gardeners: Reinvigorate bearded iris bed

Bearded iris plants put on a particularly spectacular display this season. The blooms in my small garden were prolific and gorgeous! Now is a good time to evaluate how your iris plants performed this year. If the number of flowers were fewer than previous years or if the patch looks overcrowded with plants and their rhizomes, the food storing structures, it is probably time to divide them.

For these irises to perform at their best each season, a good rule of thumb is to divide the clump every four years. Late July into mid-August, or about four to six weeks after flowering, is a good time to complete the project. When divided at this time, the plants will have adequate time to re-establish their roots in the soil before freezing temperatures arrive.

Gather together a shovel or pitch fork, a sharp kitchen or garden knife, a hose, scissors, and a 9-to-1, water-to-bleach solution to disinfect your cutting tool.

Start by clipping the leaf blades back by two thirds. Next, use the pitch fork to lift the iris clump and gently set it aside. Brush or rinse the soil off the rhizomes and begin to separate them with the knife, dipping the blade into the bleach solution after each cut to reduce the chance of spreading any disease. Cut the rhizomes into smaller sections, which each have a fan of leaves, a firm, healthy section of rhizome and well-developed roots. Discard the older rhizome, which produced the smaller sections. Each will now produce one blooming stalk.

A common practice for planting the divisions is to place three rhizomes in a triangular pattern about 12 to 15 inches apart. For a large display, flip the triangle’s base for an adjacent grouping of three and continue the pattern until the desired bed size is achieved. Place each rhizome on a small mound of soil and spread the roots out around it. Fill in with soil and cover so that the rhizome is barely visible.

Bearded iris thrive in full sun in a well-drained soil. They are not heavy feeders and so need little to no extra fertilizer when grown in a fertile soil. A balanced 10-10-10 fertilizer can be used in the spring and again after flowering, applying 1 pound per 100 square feet.

Email your home garden and lawn questions to uiemg-dupage@illinois.edu or call the Master Gardener Helpline at 630-955-1123. Visit our website at http://web.extension.illinois.edu/dkk/.

Julie Moore has been a master gardener volunteer with the University of Illinois Extension in DuPage County for 10 years and has a degree in ornamental horticulture from the University of Illinois.

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