7 Perennials You Should Divide in the Fall
Get more plants for less by dividing perennials at the right time.
Dividing plants is good for the look and health of your garden. Overcrowded plants compete for resources, and they’re more at risk for plant diseases. Dividing is also an easy way to get cheap plants. You can divide and replant in your yard, or give away the extras to friends and neighbors. To divide plants successfully, timing is important.
When to Divide Plants
“Plants that are stressed and need to be divided will show you signs that they need to be split up,” says Shelby DeVore, founder of Farminence. “They may bloom less, or have smaller blooms. You might notice a ‘bald spot’ in the center of the plant. Or certain stems of the plant may need to be staked up in order to keep them from falling over.”
Dividing plants, like pruning, is a seasonal chore. The same rule of thumb applies: Divide spring-blooming plants in the fall and fall-blooming plants in the spring. But there’s another indicator of when to divide plants — their roots.
“Generally speaking, perennials that have a tuberous bulb should be divided in the spring,” DeVore says. “Plants that have fleshy roots can be divided in the fall.“
Most plants do not need to be divided every year. Some are best divided every few years; others can go for a decade or more before it’s time for a trim. It’s also best to divide plants on a cool, cloudy day to prevent the sun from drying them out.
How to Divide Perennials
To divide a plant, first dig up the entire plant. Then brush or shake off as much dirt as you can from the roots. “Most fall-dividing perennials can be easily pulled apart,” says DeVore. Use your hands or garden forks to separate the plants.
“For roots that are tough to break apart, you can use a spade or small hand saw to cut through them,” says DeVore. “It sounds aggressive, but you won’t cause any lasting damage to the plant by separating them this way.” Dividing plants in the spring tends to take more effort.
Once they are divided, plant them wherever you like. They can go back in the ground or into pots to be shared. Place them in rich soil and keep them watered — you may want to add soil amendments before replanting. When dividing plants in the fall, DeVore says, “make sure that your plants have at least six weeks to grow before your first average frost date.”
Here are seven perennials to divide in the fall and five to leave until spring.
Peonies are loved for their showy blossoms and sweet scent. They’re easy, long-lived plants that can survive even harsh Minnesota winters. They don’t need to be divided often, but they handle it well. DeVore recommends dividing in the fall. Each peony division should have three to six eyes.
Daylilies provide season-long color with continuous summer blooms. They’re available in many bright colors. Summer-blooming plants like daylilies can usually be divided before or after they bloom.
When dividing daylilies in fall, Iowa State University Extension recommends cutting back the foliage to six to eight inches. Each division should have two or three fans of leaves. Daylilies should be cut back in the fall even if you don’t divide them.
Fall: Oriental Poppies
Poppies are next on the list for fall division, according to Ronnie Collins, founder of the Electro Garden Tools blog. These happy flowers are most well-known for large, scarlet blossoms, but there are many types of poppies with many colors. Divide these plants when they die back in the fall.
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Fall: Siberian Iris
This smaller iris variety is well-loved for its attractive foliage and graceful flowers. DeVore and Collins both recommend dividing Siberian iris plants in the fall. Divide these similarly to daylilies: Cut back the foliage, keeping about three fans of leaves and maintaining a good root system for each division.
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Fall: Garden phlox
This long-blooming perennial has large, showy clusters of flowers that dazzle all summer.
When dividing garden phlox in the fall, Iowa State University Extension recommends mulching after replanting: “A four- to six-inch-layer of straw, pine needles, or similar material should prevent repeated freezing and thawing of the soil that could heave late summer/early fall planted divisions.”
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Fall: Bleeding Heart
Bleeding heart plants don’t have the longest blooming season, but it makes up for time with quality and resilience. This woodland garden staple’s heart-shaped flowers dazzle gardeners every spring.
According to the University of Wisconsin Madison Division of Extension, self-seeded plants take several years to bloom, so propagation by division is a popular option. Collins recommends dividing in fall.
Caring for hostas is easy, especially when you divide them at appropriate intervals. Split hostas in the spring every three to five years, or as they start to show signs of overcrowding. You may be able to divide small hostas with your hands. Large hostas will need to be split with a spade.
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Spring: Black-eyed Susans
DeVore also recommends dividing black-eyed Susans in the spring. As they reseed, these quintessential summer flowers grow more and more crowded. Divide them before they start to flower.
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Divide asters in early spring, just as they start to show new growth. Iowa State University Extension recommends dividing aster clumps with a sharp knife. Keep several shoots and roots for each division.
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Spring: Ornamental grasses
Perennial ornamental grasses should also be divided in the spring, since they bloom or seed in late summer and fall. Spring division is most strongly recommended for warm season grasses, according to Colorado State University extension. Cut back the grass before digging up the clump and remove dead or diseased portions by hand.
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Succulents are ideal plants for propagation, and stonecrop, AKA sedum, is no exception. There are countless varieties of stonecrop. One of the most popular choices for home landscaping is autumn joy sedum, a hardy, upright variety with fall blooms. Divide these in early spring.