Late summer and early fall is a great time to evaluate the garden and take note of the perennials that would benefit from division. When to divide and how to divide is a frequent question.
A good rule of thumb is to divide spring flowering plants in early fall and summer flowering plants in early spring. But divisions can happen throughout the summer as long as a plant is not divided when it is flowering. Summer divisions just require a bit of extra care. My garden had a stunning clump of Becky Shasta daisies that I had neglected to divide last fall. As a result, light was limited to two nearby shrubs. Division of the daisies took place at the end of July when their bloom period was over for the season. All foliage and stems were cut to the base of the plant. The spreading clumps were dug out and relocated to other spots in the garden. Extra care and additional watering were done over the following weeks to assure that the roots were established in their new locations.
A plant will usually give you indications of when division is needed. Signs to look for are smaller flowers and fewer flowers, smaller leaves, or plants that seem to die out in the center. As you become more familiar with garden perennials you will easily recognize these signs. Division makes for a healthier plant and with less crowding the plant has a better bloom period.
You need to familiarize yourself with a plant’s growing habit. Some perennials need division every 2-3 years, whereas others may be able to go 5-6 years before division is necessary. Some perennials don’t need dividing at all. In fact, there are many plants that resent division as they grow with long tap roots which make division impossible. If you have never divided a perennial plant, start with ones that are easy to re-establish, such as sedums or daylilies. It will give you confidence as you hone your gardening skills.
Division can be done in two ways. If you have a clump forming plant, the entire plant should be dug out of the ground. A pitch fork works great for this job. The clump should be cut into sections with a knife or small saw. Don’t make the clumps too small as they may break apart in the process of replanting. The new clumps should be replanted and given extra attention as they re-establish in their new locations. Large clumps of sedum are easy to divide in spring just as new growth is starting to show. Daylilies can be divided in spring also, but do just as well with divisions in fall as soon as their flowering is complete. Plants that spread, such as bee balm, don’t need to be totally uprooted. A section of the spreading plant can simply be removed from the edge. A sharp spade or pitch fork also works great for this job.
The list of perennials that benefit from division is long. The few examples I have noted in this article may get you started. Don’t be afraid to give plant division a try. I experimented with a perennial in my garden last fall. The entire clump had a very twisting root system. I washed off all of the dirt, and separated the twisting roots. I immediately replanted the plants. The results were wonderful. I had many new plants this summer that flowered more profusely than the original parent plant. More importantly, I added to my growing knowledge about dividing perennials.
Until next time. . . happy gardening.
Nina Binkley, U.W. Extension Master Gardener Volunteer