COLUMBIA, Mo.– Some perennials can suffer from too much of a good thing.

As it grows year after year, the perennial’s growth clump, or crown, gets so big the plant begins to compete with itself for light, water and nutrients. Eventually this self-competition will mean fewer and less-showy flowers.

Not all is lost, said David Trinklein, horticulture specialist for University of Missouri Extension. A little garden surgery can breathe new life into tired perennials.

“Rejuvenating usually means just dividing the clump. Take a very sharp spade and go right down the middle of the plant,” Trinklein said.

Remove one half of the clump, making sure to take as many roots as possible with it. Now the original plant will increase root growth over the winter and be ready for bloom in the spring. Plant the other half as is, or divide it further into quarters or eighths and share the wealth.

“Very few plant people will throw a plant away,” he said. “They can use that portion of the removed perennial to expand their garden or give them to family, friends and neighbors.”

You might think of dividing and re-planting as a spring chore. “Not so,” Trinklein says.

Dividing in the fall avoids summer heat and water stress. “Because the divided plant has suffered some root damage, it needs time to reestablish its root system,” he said.

There’s a tendency to judge the growing season by the vegetative growth above the ground, but root growth continues much later into the season, he said.

“Roots cannot tell length of day or night. As long as the soil temperature is relatively warm, roots will continue to grow.”

Dividing perennials isn’t necessary for all plants. Trinklein says peonies are good examples of plants that don’t like to be disturbed. Perennials that do lend themselves well to division include black-eyed Susan, fountain grass, hostas and purple coneflowers.

There is one caveat: Whether you’re reestablishing plants from the new divisions or encouraging new growth from the remaining part of the plant, avoid adding fertilizer during the fall, Trinklein said. Fertilizer stimulates vegetative growth, which can put the plant at risk if there’s a severely cold winter.

“Wait and apply fertilizer whenever the plants break dormancy the following spring,” Trinklein said. “That’s the time to fertilize perennials.”

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