Iris come in so many colors they are often referred to as rainbow flowers. To keep them producing flowers they need to be dug and divided every two to four years. When the clumps start bumping into each other and the centers are filled with brown dead clumps, they are telling you they need more room.
Digging is best done any time from mid-July to early September. A forked spade works best but a shovel works too. Work around the outside edges of the clumps, lifting as you go until you can pull the clump out of the ground with your hands. The clump may look like a gnarly mess but there is logic to it. In the center is the “mother rhizome”, which in many cases will not have any leaves. It looks like a potato with other smaller potatoes attached. Start working from the outside, breaking apart each clump in separate rhizomes. Any rhizome with a blossom stalk attached will not bloom again and is discarded. All of the inner rhizomes without leaves are also discarded. You will still have a good number of rhizomes with leaves when you are done.
For ease of handling and replanting, trim leaves and roots as shown in photos. If you have several colors or know the variety and want to be sure you replant some of each kind, mark a leaf of each rhizome or keep varieties separated into paper bags. For ease of handling and replanting, trim leaves and roots as shown in the photos.
Rhizomes can then be washed with a kitchen dish brush or strong spray of water. If you have any rot in your iris patch, it is recommended that the rhizomes be sanitized then with bleach (1/4 cup in a gallon of water) for 1-2 minutes. Lay them out to dry.
They are now ready to replant. If you are unable to plant them at this time, iris rhizomes can be kept in a cool dry area for a week or two. Add mushroom compost and high phosphate fertilizer to the soil before replanting. Most new growth come from the “heel” of the rhizome (where the leaves are). Allow space for growth in that direction when planting and place them two feet apart. The rhizome will sit close to the surface with just enough covering to hold it in place. Water every few days if no rain to keep the soil from drying out. By the end of October, they will have put out new leaves and growth for next year’s flowers. Smaller rhizomes may take two years to put out blooms.
If you love Iris, check out the Aril and Iris Society of Albuquerque. You can contact Rae Phillips, president at: 505-235-5992 or raecyp65@gmail.com. Meetings are monthly at the Albuquerque Garden Center, 10120 Lomas Blvd NE.
Edith Iwan is a Master Gardener who lives and works in Thoreau. As a Master Gardener she assists the County Cooperative Extension Service in providing accurate, research-based gardening information to county residents. If you have any gardening questions, please call the NMSU Cibola County Extension at 505-287-9266 or NMSU McKinley County Extension at 505-863-3432.