KState Extension: Irises, Daylilies and Peonies – Now is the Time to Divide

Submitted by Krista Harding

School is starting this week for many area students and I feel like summer is winding down. I have enjoyed the cooler August temperatures and abundant rainfall! We have certainly not worried about drought stress in our area this year, which is always a plus in my books. As we head to the middle of August with our landscapes, it is time to divide plants and get them ready for the winter months ahead. Irises, daylilies and peonies are all very popular perennials and can be divided now.

Irises are usually divided in July and August. When dividing irises, it is best to look for a “double fan” – a large root with two leaf fans growing off of it. A plant with a double fan will bloom much quicker – possibly the year after planting.

Start by digging out all the iris and set them in a bucket of water to wash the soil from the roots and the rhizomes. Rhizomes are the thick, horizontal stems from which the roots grow and where buds are present. Healthy rhizomes should be blemish-free and no less than one-inch in diameter. Discard any sections that show signs of disease.

Use a sharp knife and cut off any sections of rhizomes without leaves or buds. The goal is to wind up with five- to seven-inch sections of healthy rhizomes with at least one good fan of leaves and two or more buds. Dip the knife in a bleach solution between cuts to prevent the spread of disease.

Plant the iris in soil ridges, 12 inches apart and in rows. Spread the roots on both sides of the soil ridge and then pat the soil around the roots. The soil should never cover the rhizome, but should hug the sides of it. Pat the roots in to keep the fans upright. Water immediately and continue to water until the plants are well established.

Daylilies need to be divided every three to four years to maintain vigor. Though they may be divided in early spring before growth starts, it is more common to divide them this time of year. Many gardeners will cut back the tops to about half their original height to make plants easier to handle.

A spading fork can be used to peel fans from the existing clump. If the plants have been in place for a long time, it may better to divide them by digging up the whole clump. Divide each clump to about the size of a head of cauliflower. Space divisions 24 to 30 inches apart and set each back to its original depth.

Peonies, on the other hand, may never need to be divided and may live 50 years or more without being disturbed. Peonies do not require regular division for successful blooming the way some other perennials do. Division can be done though, to increase the planting area or if the plants are growing poorly.

Division of peonies should be done after September 1, but early enough to give them plenty of time to get situated before the ground freezes. Here again, cutting the foliage back at ground level will help aid in easier handling. Each root division should have at least three to five “eyes.” The “eyes” actually look more like pink noses and are the shoots for the next season.

Peonies need to be set in a hole that is 18 inches deep and across. The hole should be refilled half way with a mix that is one part organic material and two parts soil. The eyes should be planted about one to two inches deep. If planted too deeply, the plant will produce foliage and no flowers.

Krista Harding is a K-State Research and Extension Agricultural agent assigned to Southwind District. She may be reached at [email protected] or 620-244-3826.

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