Digging, Dividing & Replanting Tall Bearded Iris

By Carrie Winter

So your tall bearded irises simply did not bloom well this year, despite having produced many bloom in previous years . . . What’s the problem?  If the clumps have been in place three or more years, it’s time to dig, divide and replant.

The ideal time to dig is when the rhizome (actually an enlarged stem, but often called bulb, tuber or root by non-Master Gardeners) is fully mature and on the brink of summer dormancy.  That time for the Charlotte, NC, area is July, not the most pleasant time for digging in the garden.  However, since the rhizomes are growing near the soil surface, a clump is really quite easy to dig with a garden fork or shovel.  Simply slide the fork or shovel under the clump, raise it up, and place the clump in a tub or on a plastic sheet.  If you are digging more than one variety, it is important to keep them separate and properly labeled.

Remove the soil from the rhizomes and, with your hands or a knife, separate the clump into individual rhizomes with a fan of foliage.  Examine each of the fans or divisions carefully for evidence of disease, especially rot.  Discard these and the “mother” rhizome of the clump, saving all the young and healthy rhizomes.  Trim the foliage of the fans to be saved into an inverted vee about six inches high.

At this point, the trimmed rhizomes can be washed, drained and dipped into a solution of 9 parts water to 1 part bleach, rinsed and drained again.  The rhizomes should then be allowed to dry in shade that is open and dry.  Most home gardeners generally omit the washing and rinsing steps.  Rhizomes may be left out of the ground for up to several weeks, if necessary.

Now you are ready to replant.  Before the dig or while the rhizomes have been drying out, the replanting area should be prepared.  Your site should be well drained and receive at least six hours of full sun for maximum bloom.  Dig the area to a depth of 10-12 inches and add soil conditioner, low nitrogen fertilizer and a dash of superphosphate.  Lime is typically a useful and often necessary additive to Mecklenburg County clay to achieve a pH of 6.1-7.2.  Work in the additives carefully so that none of the fertilizers will rest on the rhizomes.

The rhizomes of tall bearded iris should be placed 12-18 inches apart.  If you have 3 rhizomes of the same variety, you may want to plant them in a triangle to achieve an immediate clump effect.  The toe of each of the rhizomes should point to the center of the triangle.  Each rhizome should be planted horizontally on a slight ridge so that the roots can spread out on both sides of the ridge.  Cover the rhizome while leaving the upper surface of the rhizome exposed to the sun.  Secure the roots in the soil and water well for the first week or two while a good root system develops.  After that time, watering of bearded irises in the Charlotte, NC area should not be necessary, making them an ideal plant for water conservation during our hot, dry summers. 

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