Fall is right around the corner, and it is time to begin the process of closing down our gardens for the winter months to come.
As I look around my garden, I realize it is time for an annual check of my hybrid irises. I will be checking them for a couple of things: overcrowding and disease.
Irises multiply quickly, with overcrowding leading to fewer and smaller blooms. Plan on dividing every three to four years. Irises are ready to be divided when a clump looks overgrown with rhizomes growing into each other and popping up from the soil. You also may notice only growth along the outside perimeter with no growth in the center of your plants. Those center rhizomes will no longer produce blooms, so it is time to remove them.
As a rule, the best time to divide irises is July through September. However, with hotter and dryer summers, we are finding, at least here in Oklahoma, that waiting until September is best for the iris as well as the gardener. After all, who wants to be outside working in triple digit temps?
To divide your iris, start by lifting the old clump of iris out of the ground. I personally prefer to use a potato fork for this step. Wash soil from the roots and trim back healthy leaves into fan shapes 6 to 8 inches in length.
Select healthy looking rhizomes and separate those from the clump with a sharp knife. Examine the rhizomes for signs of soft mushy areas and iris borers. If you notice any of these problems, discard those rhizomes. (DO NOT COMPOST). Healthy rhizomes should be nice and firm. Next, soak the rhizomes in a weak bleach solution: 1/4 cup bleach to one gallon of water. Rinse with plain water and let dry while you prepare your new site.
Select a location with ample sunlight and good drainage. Dig a hole large enough to support one to three rhizomes. At this point, I like to amend my soil. I throw in a handful of epsom salts and bone meal. You can use a fertilizer if the nitrogen content is on the lower side. Large doses of nitrogen can lead to an overgrowth of foliage and problems with rot due to poor air circulation. Mix everything together in the plant hole with your hands, forming a mound on which to lay your rhizomes. Arrange and point the rhizomes away from each other approximately 12 inches apart. Spread the roots out over the mound, secure using a landscape pin over the top of the rhizome and cover with soil. Be sure not to plant too deep. (Shallow is good!!!) Water in well.
Proper and routine garden sanitation, such as keeping an accumulation of dead leaves off your irises, will be your best defense against common iris problems and disease.
Looking for new varieties of irises? Check out your local Iris Society. Their annual Rhizome Sale is scheduled for Sept. 25 at the OSU Extension Center in Enid. There will be people on site to answer all your questions.
While you are there, take time to stroll through the Master Gardener Demonstration Garden. The garden has been absolutely beautiful this year.