Welcome to autumn! A time of cider presses, pumpkin carvings, leaves turning color, and plant division. As our landscapes put on their coat of many colors and shine with the beauty of falling leaves, we need to think about dividing some of our perennials. Many gardeners prefer to divide perennials in the spring, before plants have set foliage, flowers, and fruit. But fall is a great time to divide peonies, iris, and daylilies.
Daylily divided using soil knife.
Starting the first week of September, I begin cutting the foliage off of daylilies in all my landscapes. This rejuvenates the plant for a few more weeks until that hard freeze in early October. I may even get some more blooms from them. While doing this, it is also a great time to divide those lilies. Daylilies benefit from division every three to four years. As plants age, the clumps get larger and bloom production goes down. After division, bloom production increases and the plants are healthier. And we get free plants!
By the first week of August, peonies and iris are dormant, and the foliage can be cut back. I don’t like to cut the peony foliage back until they begin to yellow, or if they have mildew. Peonies can make wonderful, shrub like fillers when they are not blooming. Iris too provides vertical structure in the landscape and I do not cut them back until September or October.
Shovels and spades can also be used to divide perennials.
Division can be done using a soil knife, spade or shovel, or just pulling apart by hand. First, dig up the plant to be divided, then shake or wash of loose soil, exposing the roots. The roots of iris, daylilies, and peonies are thickened and easy to see. Daylilies should be divided so there is at least one fan per set of roots. A daylily fan is the set of leaves arising from the roots. Irises and daylilies should be planted twelve to sixteen inches apart, and peonies should be planted eighteen to thirty-six inches apart. When planting irises, be sure only the stringy roots are buried, the rhizomes should be above the soil level, and not mulched over. Iris rhizomes can rot if planted to deep.