As the days shorten, plant growth slows toward dormancy; this is the time to divide perennial flowers.
Before you grab the spading fork, consider why you are digging into the root mass of a plant:
♦ You have friends who have been coveting the plant, and you are willing to share.
♦ You want to create more plants to fill in a portion of your landscape.
♦ The plant will bloom more profusely if it is not as crowded.
♦ The plant has become a thug and out-grown the space allotted for it.
♦ It is the wrong plant in the wrong place.
Dig the plants in the early morning or early evening after you have thoroughly wetted the soil the plant is growing in, and the soil in the spot to which you are moving some of the divisions. Dig close to the parent plant so you know that the roots you are lifting are from the plant you want to divide. Often the plant you want to divide, such as a daylily, has multiple crowns, which can be teased apart.
I like to use a spading fork to lift parts of the root and then use an old bread knife or a pruner to cut out the parts I want to sever. Cutting with blunt force from a shovel can damage both the parent plant and the divisions you are creating. Some plants such as Astilbe may have such a large root mass that an old saw is the best tool for creating root divisions.
Throw out any diseased parts. And if root weevils have been noshing on the leaves of a particular plant, wash all the soil from the roots of the plant before moving it to the new locations to prevent moving the insect pest to a new area of your landscape.
So, your friends want some plants. Give them a heads-up so they can prepare the site in their yard — otherwise many shared plants languish in a half-filled pot of soil or in a plastic bag, and that is not a happy way to start life as a transplanted flower.
Be sure your transplanted divisions that will fill-in your landscape actually have sufficient light and water to thrive. Most perennials require full sun. Assessing the environment will prevent you wasting your time moving plants to areas where they will not grow happily — instead, you could be spending your time reading a novel and drinking lemonade to create a special, successful scenario for yourself.
Many plants need to be thinned in order to bloom consistently. The classic is iris that need to be spaced so that each rhizome is exposed to a few hours of direct sunlight each day. Another classic perennial is strawberry; the “mother” plant grows vigorously for only two or three years, and then must be removed to make room for the divisions it has created in the space around it.
If the plant has become a thug and grown more vigorously than you imagined it would, do you really want to transplant divisions into other portions of your landscape?
If you can’t convince unsuspecting friends to take the divisions, be tough and throw the divisions in the green can. Put them in the compost after allowing them to dry thoroughly so they cannot sprout and overtake your compost pile. People have the hardest time throwing away plants even though they are not sentient beings! I am always suspicious when people offer extra plants because I fear an extra exuberant is lurking in that pile of offered offshoots.
The same considerations should be applied to the wrong plant in the wrong place. Do you actually have space for the plant to grow properly when you move the divisions? If so, move the divisions, grit your teeth, and pull out the entire parent plant. The wrong plant in the wrong place — be it the wrong size, texture, color or growth habit — will torment you for another season if you do not deal with it this August.
Some plants such as peonies will not take lightly to having the roots disturbed. Don’t be disappointed if the plant takes a year off to re-establish its roots before it blooms.
Have a wonderful time beginning your fall gardening season.
A WSU Master Gardeners of Chelan County column appears weekly in The Wenatchee World. Bonnie Orr is one of four columnists featured.