There are three reasons to divide perennial flowers: to increase the number of plants, to help rejuvenate the plant, and to control the size of the clump. Most perennials should be divided every three to five years, although plants that are growing and blooming well are best left alone unless you just want more of the same plant. You should divide your perennial if its flowers are smaller than normal, if the centers of the clumps are hollow and dead, or if the bottom foliage is sparse and poor.
You can divide perennials in either spring or fall. Plan to divide your perennials four to six weeks before a hard freeze. It is better not to divide a perennial on a hot, sunny fall day, so wait until you have a cloudy day or even just after a rain.
It’s best to divide perennials when they are not flowering so that all the plant’s energy can go to the development of roots and leaves. Here are some tips to help you be successful when you divide.
Plan ahead: A day or two before dividing your plants, water them thoroughly. Prepare the areas where you plan to put your new divisions before you lift up the parent plant. Prune the stems and foliage to six inches from the ground to ease division.
Lift up the parent plant: Use a sharp shovel or spade fork to lift or dig the plant on all four sides about four inches away from the plant. Pry underneath with your tool until the whole clump comes up. If the plant is large and heavy, you may need to cut it into several pieces with your shovel before you lift it out of the hole. Otherwise, lift the whole plant and then cut it into pieces.
Separate the plant: Shake or hose off loose soil and remove all the dead leaves and stems. Perennials have different root systems and each one needs to be treated a little differently.
Spreading root system: These have slender, matted roots that originate from many locations with no distinct pattern. They can usually be pulled apart by hand or cut apart with shears.
Clumping root system: These have a central clump with multiple growing points. Many have thick, fleshy roots. You may have to cut through the thick, fleshy crown with a knife. You may be able to use a digging fork to pry this perennial apart. Keep at least one developing eye or bud with each division.
Rhizome division: Rhizomes are stems that grow horizontally or above the soil. After lifting, cut and discard the rhizome sections’ one-year tubers, cut apart after lifting with a sharp knife. Every division should have a piece of the original stem and a growth bud attached. You can even store your tubers for spring planting.
Large, tough roots: If the root mass is large, tight, or tangled, you can pick up the clump, then drop it on the ground to loosen the root mass. Then you can pull apart the individual plants. Do not do this with plants that have brittle roots, like peonies.
Plant the divisions: Never allow the divisions to dry out. Keep water nearby to moisten divisions until you plant them. It is best to plant the divided sections right away. Water well after planting and be sure to mulch around the newly planted perennials.
Craig Mauney is a Forsyth County Extension Agent at the Cooperative Extension in Winston-Salem.