CORVALLIS, Ore. – While you’re weeding and seeding and planting and pruning, there’s one more thing to put on your plate: dividing.
Dividing is a matter of digging up plants, prying them apart with your hands, spades, knives or an ax and replanting them in new holes, said Weston Miller, a horticulturist for Oregon State University’s Extension Service. As perennials grow from the crown and the clumps get larger, plants decline in vigor and have fewer flowers. If you wait too long to divide, flowering can stop altogether.
That’s not the only reason to take out the spade and start splitting up your prized plants.
“I divide plants when I want more of them,” Miller said. “I’m looking outside and seeing some chives. I’ll hack those into quarters. I divide things like yarrow a lot because I want to populate large areas.”
Gardeners love to dig and divide plants and share them with friends and neighbors. However, with new threats in Oregon from invasive species like Japanese beetles and the so-called “crazy snake worm,” it is no longer recommended to move plants or soil from one location to another. Also, OSU does not recommend plant swaps or sales based on dug-up plants at this time. Refer to guidelines for Best Management Practices for plant sales.
How many more plants you end up with depends on the size and vigor of the original plant. Hosta, grasses and daylily can produce six or more, while hollyhock and coral bells may only yield three. Be sure to pay attention to how many growing points there are and leave at least two per clump when you cut plants apart.
As a general rule, Miller said, divide summer- and fall-blooming plants in spring and spring-blooming plants after they’ve bloomed or in the fall. Don’t cut apart a plant when it’s blooming.
You’ll know your plant needs dividing if it’s dying in the middle or becoming lackadaisical, he said. Even if a reference says to divide a plant every three years, there’s no need to do so if it’s growing well.
One thing people don’t think to divide are culinary herbs such as sage, thyme, oregano and marjoram, Miller said.
“You’ll get much more supple growth and better culinary quality if they’re divided every couple of years,” he said.
Miller’s advice on how to divide plants:
Miller recommends dividing these plants in spring
Divide every 1-3 years
Divide every 3-5 years
Divide every 5-10 years
About the OSU Extension Service: The Oregon State University Extension Service shares research-based knowledge with people and communities in Oregon’s 36 counties. OSU Extension addresses issues that matter to urban and rural Oregonians. OSU Extension’s partnerships and programs contribute to a healthy, prosperous and sustainable future for Oregon.