If your once lovely perennial plant is
beginning to die out in the center, it is likely not a doomed plant but is simply in need of dividing.
Perennial, by definition, means to endure or to last for a very long time. In the botanical world, a perennial is a plant that, like its definition, can endure and last for a long time, but it won't last forever. Even the hardiest perennial can tire out after a while, but that doesn't necessarily mean the plant has breathed its final molecule of carbon dioxide.
In merely means that it might be time to refresh the plant by digging it out of its tired soil, cutting it into a few sections and replanting each section to grow into fresh, new plants. It's a win-win situation for the gardener. Not only is the plant rejuvenated, but new plants are created to put elsewhere in the landscape or to give away to friends.
Late summer and fall is the best time to divide summer blooming perennials, but wait until the plants are no longer blooming. Once the plant has finished using much of its energy to create blossoms, it can then focus on strengthening its root system. By planting in late summer or early fall, the plant will still have ample time to grow strong roots and enable it to get through the coming winter.
Plants should never be divided during the hottest mid-day sun. It is best to wait for a cool, cloudy day. If there is a bit of rain in the forecast, even better.
Most plants will benefit from being lifted from the soil and then having the roots, crowns, tubers, rhizomes or bulblets divided. While every five years is a common guideline, some plants may need divided sooner if they are crowding out other plants in the garden or if they are starting to die out in the center, leaving a ring of healthy growth around a brown central crown.
Bearded iris grow from rhizomes, an underground horizontal stem. As the plants mature, they create new sections of rhizomes that can be cut away from the others. When divided, each rhizome should contain a group of leaves. Iris divisions consist of a section of rhizome with a group of leaves that are called fans. Once separated from the main clump of rhizomes, the fans should be trimmed either in a V-shape or diagonally across.
"When you only have one rhizome with all of these tall, heavy leaves, the whole thing is top-heavy,'' said Kathleen Ferris, Trumbull County Master Gardener and iris grower. "Trimming the leaves enables you to plant the rhizome, and it won't fall over and pull out of the soil,'' Ferris said.
Iris rhizomes should be planted shallowly, leaving a section of the rhizome showing above the soil surface.
But before you begin digging your plants, a little preparation is in order.
Water plants well a day or so prior to lifting them from the soil. This will loosen the roots and keep them from breaking off during the lifting process. If the plant is quite tall, prune it down a bit to make the job easier. Some plants can be cut as low as six inches from the ground.
Using a sharp spade or garden fork, dig as deep as possible around all sides of the plant. Be sure to keep a good distance from the base of the plant, usually at least six inches, to avoid damaging as many roots as possible.
Pry the plant out of the soil and shake it or hose it off to loosen clinging soil and to remove excess mulch, leaves and other debris.
Besides the rhizome root system of iris, some plants have spreading roots that are slender and matted. These plants include monarda (beebalm), lamb's ear (Stachys byzantina), coneflower (Echinacea purpurea), and most common garden perennials. In most cases, the roots of these plants can be pulled apart or cut apart with a sharp knife.
Other plants, including the hostas, most daylilies and ornamental grasses, have clumping root systems with central crowns. These must always be cut into sections with a sharp knife or cut apart with two back-to-back digging forks. When dividing crowns, be sure to leave several "eyes" or growth buds in each division.
Tuberous rooted plants, such as dahlias, are divided by cutting the tubers apart with a sharp knife. Like the crowns, be sure to leave a piece of the original stem and each division also must have an "eye" or growth bud attached. In our area of the country, dahlias are stored for the winter and replanted in spring.
Not all plants can be divided. Woody ornamentals, such as Santolina (lavender cotton), rosemary, roses and other shrubs can be propagated by other means, but not by dividing them at the base.
Once you have divided your plants into sections, with the exception of tubers and corms that should be stored over winter, replant the sections at the same planting depth they originally grew. Water well and mulch for winter protection. When mulching, leave a distance of at least two inches from the base of the plant to keep from smothering tender young stems and to keep pests from having a hiding place where they can relax and gnaw on your new plants.
Replant the divisions as soon as possible. If they can't be planted right away, lay your plants on the ground and cover with moist soil to keep the roots from drying out.
For more information on dividing and propagating plants, contact The Ohio State University Extension Trumbull County Master Gardener hotline at 330-637-3908 or e-mail firstname.lastname@example.org.
Evanoff is a Master Gardener with The Ohio State University Extension of Trumbull County. She can be reached at email@example.com.