Dividing and replanting keeps spreading perennials under control. Dividing will rejuvenate old plants, keep them vigorous, and bloom freely. Dividing perennials is very easy and inexpensive way to gain additional plants for your garden or to pass along to a friend.
Division is the quickest way to propagate perennials such as daylilies, coneflowers, black-eyed susans, and hostas. These perennials can be divided once they have been in the ground for three years or more. Division can also be used on containerized plants bought in garden centers as long as the plants are well-rooted. Some nursery growers often place more than one plant per pot in order to make the plant sell faster. This is an advantage to gardeners, because one purchased plant may then be divided into two or three plants.
The easiest technique to divide perennials is to use a clean sharp shovel, saw or knife to literally cut up the root ball.
The best method, that will preserve the root system, is to place the clump into water to remove the excess soil. This allows the roots to be loosened, and individual plants may be easily pulled apart.
In general, divide spring and summer blooming perennials in the fall, and fall bloomers in the spring. By diving the plant when it is not flowering, all the plant’s energy can go to root and leaf growth. Division should occur between early September in the upper Piedmont and mid to late October along the coast. When dividing in the spring, allow enough time for roots to start to establish before hot weather. Spring divided perennials often bloom a little later than usual.
Most perennials should be divided every three to five years. Some perennials such as chrysanthemums and asters, may need to be divided every one or two years, or they will crowd themselves into non-flowering clumps of leaves and roots. Bleeding hearts and peonies may never need to be divided unless you want to increase your stock.
How do you know when your perennials need to be divided? Look for signs of smaller than normal flowers, centers of the clumps that are hollow and dead, or when the bottom foliage is sparse and poor. Plants that are growing and blooming well should be left alone unless more plants are wanted.
Preparing your to be divided plants ahead of time is very important. Water plants to be divided thoroughly a day or two before you plan to divide them Prepare the area that you plan to put your new divisions in before you lift the parent plant. Prune the stems and foliage to 6 inches from the ground in order to ease division and to cut down on moisture loss.
Use a sharp pointed shovel or spading fork to dig down deep on all four sides of the parent plant, about 4 to 6 inches away from the plant. Pry underneath with your tool and lift the whole clump to be divided. If the parent plant is very large and heavy, you may need to cut it into several pieces in place with your shovel before lifting it.
Shake or hose off loose soil and remove dead leaves and stems. This will help loosen tangled root balls and make it easier to see what you are doing. Replant the divisions immediately. Do not let the divisions dry out. Replant the divisions at the same depth they were originally. Water well after planting.
Some plants resent being divided and it should be avoided if possible. These include butterfly weed (Asclepias), euphorbias, oriental poppies, baby’s breath (Gypsophila), gas plant (Dictamnus albus), Japanese anemones, false indigo (Baptisia), and columbines (Aquilegia). Lenten and Christmas roses (Helleborus) are very difficult to move when more than a few years old. Usually you can find tiny seedlings around the base. These are easy to move.
Lavender cotton (Santolina chamaecyparrus) and several other perennials are actually small woody shrubs and should not be divided. These include perennial candytuft (Iberis sempervirens), lavender, rosemary, southernwood (Artemesia abrotanum), and several other artemesias. These plants often have rooted layers (branches that have developed roots while touching the soil). The layers can be cut off the parent plant, dug up, and replanted as though they were divisions.
For more information on dividing perennials, please visit the Home and Garden Information Center website at hgic.clemson.edu. Tune in on Tuesday nights to watch “Making it Grow” at 7pm on SCETV or mig.org. Email Outen at callenb@clemson.edu.
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