The three main reasons for dividing perennials are to control the size of the plants, to help rejuvenate them, and to increase their number. Dividing and replanting keeps rapidly spreading perennials under control. Dividing will rejuvenate old plants, keeping them vigorous and blooming freely. Dividing perennials is an easy and inexpensive way to gain additional plants for your garden or to share.
When to divide
In general, it is best to divide spring and summer blooming perennials in the fall, and fall bloomers in spring. By dividing the plant when it is not flowering, all the plant’s energy can go to root and leaf growth.
Fall division should take place between early September to mid- to late October on the coast. Allow at least four to six weeks before the ground freezes for the plants to become established.
If you divide in the spring, allow enough time for roots to settle in before hot weather. Spring division is ideally done in the early spring as soon as the growing tips of the plant have emerged. Spring divided perennials often bloom a little later than usual.
Never divide perennials on hot, sunny days. Wait until a cloudy day, ideally with several days of light rain in the forecast.
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.
Signs that perennials need dividing are flowers that are smaller than normal, 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.
Prepare to divide ahead of time
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.
Lift the parent plant
Use a sharp pointed shovel or spading fork to dig down deep on all four sides of the 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 plant is very large and heavy, you may need to cut it into several pieces in place with your shovel before lifting it.
Separate the plant
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.
Perennials have several different types of root systems. Each of these needs to be treated a bit differently.
Plant the divisions
Never allow divisions to dry out. Keep a pail of water nearby to moisten divisions until they are planted. Trim all broken roots with a sharp knife or pruners before replanting.
Plant the divided sections immediately in the garden or in containers. Replant divisions at the same depth they were originally. Firm soil around the roots to eliminate air pockets. Water well after planting.
Fall-divided perennials should be mulched in the Upstate the first winter to prevent heaving caused by alternating shallow freezing and thawing of the soil. The best winter mulch is loose and open, such as pine straw, Christmas tree limbs, or leaves.
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