Sure, you planted perennials for a carefree, flowering garden, but you may have noticed that they’re not as attractive as they once were. Here’s how to divide them in the fall to revitalize them for the spring…
Why do it: Plant clumps take up more real estate with each passing year. Often the interior dies back, and sometimes a plant stops producing flowers altogether. Simply put, your plants are aging. It’s time to discard the inner, depleted portion and rescue the younger, outer parts.
Best candidates: This project is most successful with spring and early-summer bloomers such as peonies, irises, daylilies and coral bells.
Why fall? It’s always best to intervene during a “shoulder season” to lessen transplant trauma. Fall is better than spring because not only are the plants heading into their winter sleep (dormancy), but the periodic soaking rains that most areas get at this time of year encourage root growth.
How to divide: Don’t divide at midday when it’s hot. A cool, drizzly autumn morning or late afternoon is ideal.
With clippers or a scythe, shorten the target plants to within about six inches of the ground so they’re easier to work with. Then dig up each large clump, getting as much of the root-ball as you can (this may require digging down eight inches or even more—this is the depth of the majority of the roots). Divide the root systems into three or more smaller plants. You may need to use a sharp-edged implement such as a trowel or shovel to do this or something even bigger. I’ve used two big garden forks, back to back, to pry apart a big daylily clump—and even then, the roots separated reluctantly. If the roots are dry, hosing them down helps.
Each section you save for replanting should include a strong clump of healthy-looking roots, ones that are white and crisp. Cut off any black, wiry, damaged or rotten roots, and throw them away.
If you aren’t able to replant sections immediately, don’t let the roots dry out. Plunk the divisions in pots, and cover the roots with water…or wrap the roots in damp towels or burlap for a few hours or overnight.
How to replant: Create ample holes for each plant—how big depends on the size of the divisions, but eight inches or more, deep and wide, is a safe rule of thumb. You’ve seen how big the plants eventually get, so space them well apart so that they can fill in over time.
Also, take this opportunity to improve the soil. Dig in organic material such as equal parts of loam, dehydrated cow manure and compost. Water generously, and repeat every other day unless fall rains do the job for you.