I’m so excited about the arrival of spring that I’m gearing up for cleaning out my gardens. Perennials are just beginning to peek their faces out of the ground. This is a great time — April through early May — to divide those that need it.
Those that need it are the ones that are crowding their neighbors, overstepping their bounds, declining in vigor or looking more like a doughnut than a clump, as well as those that just didn’t flower well last year.
I also divide some plants just because I want more of them, or I want to trade them with my friends to get some of their great plants. Talk about an incentive plan.
Most perennials can be divided in the spring or fall. A few only like spring, such as primrose and anemone, or only fall, such as peonies and phlox. Dividing in the spring when there is little foliage makes it easier for the disturbed roots to maintain the plant.
Cool, overcast days are the best time to divide perennials. We’ve had plenty of those this year. Hot, dry days can stress new transplants and dry their roots before you can get them in the ground. Of course, we are all busy people, so a sunny day may be the only time available.
Either way, thoroughly water the root ball the day before. This will make removal easier and help protect the roots. On sunny days or if replanting is delayed, cover the exposed root ball with wet newspaper and place in the shade.
Here is a step-by-step plan for dividing perennials.
—Start at the drip line, where rain drips off the farthest outside edge when the plant is in full leaf. The success of transplanting divisions depends on having sufficient roots. Using a spade, make cuts around the drip line, severing extending roots. Dig down and under the plant. Use the spade as a lever, being careful not to overwork the handle and break it. Lift the plant out of the hole.
—Shake or vigorously hose the soil off the root ball to see what kind of roots you’re dealing with. There are five basic root types: clumps or offsets; surface roots, called stolons; underground running roots, called rhizomes; taproots; or woody. How you proceed depends on what root type you have.
Clumps or offsets form small plants that grow at the base of a larger plant, such as with asters, coneflowers, hostas and coreopsis. Snap the connection between any of the sections and obtain a piece with plenty of roots and three or more growing points, or “eyes.” Some clumps are so dense they have to be cut apart.
Surface roots run on or just under the soil surface. They pop up and start new plants. Cut the root between plants and you have a new separate plant. Bee balm, black-eyed Susans, creeping sedums and speedwells are surface-rooted plants.
Underground running roots can develop suckers just beyond the shade of the mother plant. These can be cut away to form a new plant. Hardy geraniums, Japanese anemones, ostrich fern and plum poppies are examples.
Plants that have taproots, like a carrot, can be divided by using a sharp knife to slice down the length of the root. Every piece that has at least one eye, some of the taproot and a few side roots is a viable division. Tap-rooted plants are balloon flower, butterfly weed, cushion spurges and oriental poppies.
Woody perennials often form roots when stems rest on the ground or are buried by mulch. Simply cutting between the rooted stem and the mother plant will create a new plant. Woody-rooted plants include candytufts, euonymus, lavenders and sages.
—Separate plants with your hands, spade, fork or knife. Axes or saws may be needed on grasses or woody roots. Always use caution with tools.
—Twenty percent to 25 percent of the plant should be replanted in your garden. Perennials multiply exponentially — one stem is likely to triple or quadruple itself each year. So, if you only cut it in half, it will more than double this season and you’ll have to divide it again next year instead of three to five years from now. Smaller sections grow more vigorously and tend to produce stronger, longer-lasting blooms. Plant divisions at the same depth as the original plant.
—Removing root balls will leave holes in your garden. Be prepared to refill them with good organic matter or compost. It renews the soil, helps maintain fertility and prevents drainage problems where the soil has settled.
Jamie Kidd is a horticulturist with K-State Research and Extension in Shawnee County.