Late July through August, when the plants are entering a dormant state, is the time to divide irises. BILL SEVIER/Courtesy
Q: I would like to share some of my irises with a neighbor. When is the best time to divide my plants? L.T., TulsaA:
Sharing or gifting plants is always a wonderful way to recycle your plants and at the same time improve your plants' health and vigor. Late July through August irises are typically entering a dormant state, which is a great time to do your dividing.
Recommended frequency for division is every three to five years to avoid overcrowding. If you don't remember the last time you divided your irises or you see a significant change in the quality and number of blooms, it is probably time.
Before you start digging and dividing, decide where you are moving your plants and prep the area. Irises have shallow root systems, so you need to dig your hole only about 5 inches deep. Choose a sunny plant site with good drainage. If necessary, now is the time to amend the soil with peat moss or compost.
The easiest way to divide your plant is to dig around the entire root system and lift everything out of the ground. Once the plant is removed, you might be able to separate the clumps by hand, or you may need to cut them apart with a spade or sharp knife. Cutting back the leaves to about one-third of their height makes them easier to work with.
The iris root or rhizome is kind of like an underground stem with the newest and most vigorous growth growing away from the center. Try to separate the clumps, leaving three to five fans of leaves per clump. Look for healthy rhizomes free from mushiness, which may indicate root rot or iris borer damage.
To place your divided clumps, create a small mound of soil in your new plant site. Let the rhizome sit atop the mound with the smaller roots trailing down the mound. Cover the roots, allowing the top of the rhizome to be slightly exposed. Planting too deep may cause the rhizome to rot. If you are placing more than one clump, space them at least 18 inches apart with the leaf fans facing the same direction.
If you have a garden-related question you would like the Master Gardeners to answer in a column, call 918-746-3701.
Gardening tips
During peak heat of summer is not the best time to use postemergent broadleaf weed killers such as those containing 2,4-D. Weeds need to be growing to be susceptible to these chemicals. Weeds will start to grow when it cools and the herbicides will be more effective.
Now is a good time to submit a soil sample to the OSU Extension office for testing. Do this before reseeding fescue or creating a garden bed this fall. Call the Master Gardener office at 918-746-3701 for instructions.
When planting fall vegetable seeds, soak them overnight prior to planting. Once planted, mulch to conserve moisture and reduce ground temperature. Provide shade during initial establishment.
Fertilization of warm-season grasses can continue if water is present for growth.
Original Print Headline: Now is time to divide your irises
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