Irises are low-maintenance plants that produce spectacular blossoms. Tall bearded irises can take heat, drought, even poor soils. But eventually, irises require dividing.
In Denver, Bob Van Liere grows 2.5 acres with about 1,000 different varieties of tall bearded irises at Iris4u Iris Garden. Affectionately known as Iris Bob, Van Liere provided a commercial iris-grower’s expert tips for dividing and transplanting irises.
Van Liere recommends dividing irises every few years. Don’t wait too long! If your plants stop flowering or produce fewer blooms or the clumps appear crowded, it’s time to thin your irises.
Irises grow from rhizomes, not bulbs. Unlike bulbs, irises need time to establish new root systems before first frost. After they flower, irises grow a new root system. Ideal iris division time falls around eight weeks after bloom. Consequently, along the Front Range, mid-July often provides a perfect time to divide irises.
• Using a garden fork or shovel, dig clumps of irises.
• Knock dirt off the clump.
• Remove decaying root system and discard any dead or dying leaves.
• Cut foliage back to six or eight inches long. Trim long leaves into short fans angled and forming a point at top.
• Cut off the “heel” of the rhizome, and allow to rest overnight to develop callous.
• Select a site that gets at least six hours of sunlight daily and has good drainage.
• Loosen soil of site where you will plant iris. You might want to add some compost.
• Van Liere labels his rhizomes, using an indelible marker.
• Position iris fans 12 to 18 inches apart to allow for growth.
• Plant iris with just enough soil to cover the rhizomes.
• Do not mulch irises or allow other plants to cover them. Rhizomes need to heat up, so keep them just below the surface of soil.
• Van Liere suggests planting the trimmed iris fans at opposing angles to prolong blooming season by providing some plants with more sun than the others.
• Van Liere recommends a low nitrogen fertilizer: 14-14-14.
• Water the transplanted iris, but do not overwater. Iris don’t like to be soggy.
For a helpful, step-by-step video demonstration featuring Iris Bob dividing iris, click this link.
To order iris from Iris4u, visit their web page. Iris4u has a limited time for iris orders. When iris are in bloom, gardens are open to the public but typically ending in the second half of July.
Dig into lots more information about irises. A fascinating plant, irises are featured in my earlier article: “Bearded iris = poor man’s orchids.”
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