Perennials are among the best type of plants to grow in the garden. Unlike annuals, they come back every year, are easy to establish and have lower maintenance requirements.
Established perennials, which by nature grow larger every year, need to be divided to help control their size, to revitalize them and also as a method of plant propagation.
How do you know if the perennials in your garden need to be divided?
During the growing season, observe the plantings for reduced flowering, stem dieback, dead centers in the clumps, and a general unhealthy appearance. In overcrowded plantings, the roots will be growing in a thick, tangled mat. If the plants are healthy in appearance, they do not need to be divided unless new plants are desired.
The best time of the year to divide perennials is during the fall after they have finished blooming and started to go dormant. Most perennials, on average, need to be divided every three to five years. Some, like chrysanthemums and asters, should be divided every year while others such as peonies and bleeding hearts, seldom, if ever, need division. Some perennials, such as Lenten roses, should never be divided since once established they are difficult to transplant.
A day or two before dividing the plants, water them thoroughly. The best method of dividing perennials is to use a shovel and dig down deep on all sides of the plant. Pry underneath the plants to lift them out of the ground, shake off the loose soil, and then remove the dead stems and leaves. Place the clump into a wheelbarrow, and then use a knife or pruners to separate the underground structures into individual plantlets.
Perennials have different types of root systems which determine the method of division. Ones with spreading roots, like Black-eyed Susan and garden phlox, have roots that lack a distinct pattern in their growth. They should be divided into smaller clumps each having a few viable shoots.
Tuberous roots, which are the potato-like structures on plants like canna lilies and dahlias, should be divided by separating the individual tubers with a sharp knife. Each tuber should have a piece of the original stem and a growth bud attaché to it. Those that spread by creeping stems like irises, (the stems growing underground are referred to as rhizomes and those above ground stolons), should be dug and separated by pruners.
Each division should have a few inches of the rhizome or stolon and a set of leaves attached to them. Clumping root systems, such as ornamental grasses, are divided using a sharp knife or a shovel to pry apart the roots to separate them into smaller clumps.
Timothy Daly is an Agricultural and Natural Resource Agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or firstname.lastname@example.org