Tall bearded iris (Iris germanica) are stunning in the June and July garden borders. A wonderful plant that can become an addiction as the vibrant color ranges and combinations are almost endless. Bearded irises do very well in northern gardens, living through severe cold winters and dessert hot summers.
Iris have rhizomes which should be planted in a shallow hole in full sun. Planted in groups of three or five will give you a well shaped mature clump. As well the rhizomes should not be completely covered with soil as this may cause them to rot. Irises must have well drained soil. Bearded iris can be infected with the worm-like iris borer. Burrowing into the rhizomes this pest leaves them hollow and mushy. A good preventative measure is to cut your iris leaves down to 6 inches after frost and remove all the clippings and debris which may be infected. This will remove most of the over wintering eggs. Irises can also fall to soft rot, in which the rhizomes become soft and rot. This often follows after a rhizome has been cut or damaged. When spotted, dig out the infected area and discard the debris in the trash, not your compost pile. Replant the remaining rhizomes in a different area.
After a few years your mature iris clumps will become overgrown, crowed and blooming will be reduced. This is when they need to be revived. This usually takes about three to four years and late summer or early fall will be your best time to divide iris.
How to Divide Irises
Dig up the whole clump of iris.
Shake off the soil and examine the rhizomes for any damage or rot.
Peel off brown dry leaves and cut leaves back to 6 inches. Discard the old center rhizome into the trash, not the compost.
From around the clumps edges cut out new rhizomes each having one or 2 fans of leaves.
Allow the rhizomes to dry out overnight to allow any cuts to seal over before planting.
Replant 1 inch deep in rich organic soil and 2inches deep in sandy soil. Build a small mound in center of your hole, set rhizome on top and spread out the roots.
Face the fans all in the same direction then fill hole and pack firmly.
Properly cared for your bearded iris will last a lifetime, with many extras to move around your garden or share.