Chrissy Wen, Walworth Co. UW-Extension Horticulture Educator
I’ve always said that plants are smart. This time of year it’s hard to tell, but I’m sure we’ve all seen a plant that is growing in the shape of a donut with all the lush growth on the outside and nothing left in the middle. This is the plant’s way of begging to be divided. It’s telling you that it wants to have that shovel rip through its roots and fingers tearing apart the crown. Not only is it good for the plant, especially because plants like this can have decreased blooms, it’s also good exercise and quite therapeutic!
Fall is a great time to divide perennials that have outgrown their original homes. Warm soil helps root growth continue, sometimes well beyond when there is a chill in the air. There are some things to keep in mind that will make the task much easier on your body and on the plant. First off, have tools that work! The tools that I use most when dividing plants are an old bread knife (I get mine from Goodwill for less than a dollar) and a sharp, flat-head shovel. There are many shovels out there that will work just fine; my favorite is called the “King of Spades”, not cheap, but amazing! Also, a good pair of gloves comes in handy.
Dividing perennials in the fall is fairly easy. First, cut the leaves back to about 4-6 inches – this helps get the plant under control and makes the plant more manageable. Second, dig the entire plant up from the ground. After the entire plant is removed slice/cut/tear apart the plant into sections. (It’s completely normal to have leaves and roots fall off during this process!) Voilà, each new individual section should have roots, leaves, and stems and is ready to be replanted! Once a new home is found water the plant until the ground freezes and mulch if possible.
Spring blooming perennials prefer to be divided in the fall: iris, peony, bleeding heart, etc. On the other hand, I recommend dividing ornamental grass in the spring for a couple reasons. First, they definitely need to be cut back before dividing to keep you sane. I recommend doing this in spring to prevent crown injury. Second, they also serve as winter interest in the landscape. Hostas are another common perennial that thrives when divided. I like to divide hostas in the spring, though they can tolerate being divided really any time of the year.
When I teach about dividing plants I commonly share that spring and fall are best for dividing, but sometimes we just have to do it when we have time! If you only have time in the middle of summer, try to divide when the weather is cool, the soil is moist, and the plant is not flowering. Enjoy these last couple of months in the garden!