Fall is a good time to divide most perennials

By Marilyn McKinley

OSU master gardener volunteer

It’s hard to think about falling leaves, frost, and frozen ground – especially after the last two winters. But, it’s time. It’s time to think about what we can get done before the good weather is past us. Late summer and early fall is the time to divide most perennials to achieve the best performance next summer.

Most perennials should be divided every 3 to 5 years. The plant will send signals when it is ready to be divided: Reduced bloom size; center dying out, leaving a gap with the plant flopping around the edges. Other reasons, you may also want to increase the number of plants or control size and spread.

Fall division should take place before four to six weeks before the first freeze, thus allowing the plant to develop a strong root system. We’re pushing this time frame, but it can still be done.

Prepare the new planting location ahead of time. Try to divide and replant on a cloudy day. Never let the root ball dry out. Trim all broken roots with a sharp knife. Replant at the same depth. Firm soil around the new plant to eliminate air pockets. Water well after replanting. Use of a root promoter is a good option. Continue to water frequently.

Know and understand the type of root system you are dealing with before you dig.

Spreading – These root systems have many slender matted roots that originate from many locations with no distinct pattern. Asters, bee balm, lamb’s ear are examples. They can crowd out their own centers. Usually they can be pulled apart by hand, or you may cut apart with a knife.

Clumping – These perennials come from a central clump with multiple growing points. You will probably need a sharp knife to pry apart the thick fleshy crowns. Examples are: Astible, hosta, daylilies, and ornamental grasses. Keep at least one eye or bud with each division.

Rhizomes – These are stems that grow horizontally at or above ground level. Bearded irises are the most common perennial with this root system. Cut back and discard any section that is 1 year or older. Inspect for disease or insect damage. Iris rhizomes should include a few inches of rhizome and one fan of leaves.

Tuberous – Dahlias are an example and should be cut apart with a sharp knife. Every division must have a piece of the original stem and a growth bud attached. After division they may be stored for spring planting. However, I prefer storing and waiting until spring to separate.

To raise the root ball use a pitch fork, dig all the way around the plant then gently lift. If the root ball is large with a vigorous root system, don’t be gentle. You may need a shovel to lift and an axe or saw to divide.

Avoid dividing these plants if possible: Butterfly weed, baby’s breath, false indigo, Japanese anemone, and columbines. Hellebores are very difficult to move especially if the plant is old.

For tips and list of plants along with how to divide specific plants, goto: http://go.osu.edu/falldivide.