Irises, Daylilies, and Peonies – Now Is the Time to Divide
With many area students heading back to school this week, it feels like summer is beginning to wind down. As we move into mid-August, it’s the perfect time to divide many perennial plants and prepare them for the seasons ahead. Irises, daylilies, and peonies are among the most popular garden perennials, and late summer is an ideal time to divide them.
Irises are typically divided in July and August. When selecting divisions, look for a healthy “double fan”—a large rhizome with two fans of leaves. Plants with double fans establish more quickly and may even bloom the year after planting.
Begin by digging up the entire iris clump. Place the plants in a bucket of water to wash soil from the roots and rhizomes. Rhizomes are the thick, horizontal stems from which roots and new shoots develop. Healthy rhizomes should be firm, free of blemishes, and at least one inch in diameter. Discard any sections showing signs of rot or disease.
Using a sharp knife, remove sections of rhizome that have no leaves or visible buds. Ideally, each division should be 5 to 7 inches long, with at least one healthy fan of leaves and 2 or more buds. To help prevent the spread of disease, disinfect the knife in a bleach solution between cuts.
Replant iris divisions on small soil ridges spaced about 12 inches apart. Spread the roots evenly on each side of the ridge and firm the soil around them. The rhizome itself should remain exposed on top, with soil snug against the sides but not covering it. Water thoroughly after planting and continue watering until the plants are well established.
Daylilies benefit from division every three to four years to maintain vigor and flowering. Although they can be divided in early spring before growth begins, late summer is the most common time. Many gardeners trim the foliage to about half its height before digging, making the plants easier to handle.
A spading fork can often be used to separate fans from an existing clump. If the planting is older and densely rooted, it may be easier to dig up the entire clump before dividing it. Each division should be about the size of a head of cauliflower. Replant divisions 24 to 30 inches apart at the same depth they were originally growing.
Peonies are a little different. They may never need to be divided and can thrive for 50 years or more without being disturbed. Unlike many perennials, regular division is not necessary for continued blooming. However, division is a good option if you want to expand your planting or if an older plant is declining.
Peonies should be divided after September 1, while allowing enough time for roots to establish before the ground freezes. Cutting the foliage back to ground level before digging makes the job much easier. Each root division should have three to five “eyes,” which are the pink buds that produce next year’s shoots.
When replanting, dig a hole about 18 inches wide and 18 inches deep. Refill the hole halfway with a mixture of one part organic matter and two parts soil. Position the eyes just one to two inches below the soil surface. Planting peonies too deeply often results in healthy foliage but few, if any, blooms. Keep in mind, however, that peonies often take about three years to return to full bloom and size after division.
Taking the time to divide these perennials now will help keep the plants healthy, vigorous, and productive for years to come.
Krista Harding is the K-State Extension horticulture agent for the Southwind District. She can be reached at [email protected] or 620-244-3826.
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