Keep plant roots out of sight but not out of mind

A valuable lesson in horticulture came my way 15 years ago while I was in the midst of graduate studies at Washington State University. I lived and worked on the experiment station farm in Puyallup, in the shadow of Mt. Rainier. Between trips to the Skagit River Valley cabbage fields and all-night stints in the lab, I hung out with the ornamental horticulture staff in the Plant Problems Clinic, an office where home gardeners brought samples from suffering plants, hoping for a cure.

A woman, obviously distressed, came to the clinic with a pine branch, yellow needles dropping to the floor as she pulled it from a bag. She explained that she had planted the tree as a memorial ten years before when her father died. She had watched it grow slowly, gaining only an inch or less in height each year, and now it seemed to be near death. The plant pathologist decided a site visit was in order and asked me to tag along.

The pine was indeed on its last legs, the last decade of stress and decline evident in the close spacing of the whorls of branches. Finding no helpful clues above ground, we were granted permission to dig up the tree.

It took about five minutes to unearth the tree and expose a tangled mass of thick woody roots that girdled the crown and each other with repeated circling growth. The entire root system would fit snuggly into a 2-gallon nursery container.

The woman wanted to know how this could have happened, immediately accepting the blame. What had she done wrong? We explained that the problem started long before she purchased the tree. Left in its growing container too long, the plant became “pot-bound”, its roots circling the outside of the root ball. Once planted, the roots continued to grow in a circling pattern. Some roots died while others expanded and became woody. The circling growth compressed their inner tissues and restricted the flow of water much like compressing a water hose.

Since this experience, I have learned that circling and girding roots are often responsible for the poor performance of trees and shrubs in the landscape. It is an insidious death, often taking years, and when the plant finally succumbs we shake our heads in sadness, wondering what we did wrong.

Too often I have seen landscape crews plant trees and shrubs without concern for the quality of root systems. Or they follow an old practice of “scoring” the circling roots, making vertical cuts on the outside of the root ball with a sharp knife. However, recent research has shown that this is minimally effective. And for some species, including birches and some maples, scoring the roots can lead to an increase in circling roots.

There is no cure; the only solution is to purchase plants with quality root systems. This means inspecting plant roots before we buy trees and shrubs, placing as much emphasis on the appearance of the root system as the above-ground portion.

Take the plant out of its pot! If you see extensive root circling on the outside of the root ball, don’t buy the plant! You are only buying a problem, perhaps one that will not be apparent for several years.

When you buy trees and shrubs this spring, be a smart shopper. Remember that intensive nursery production methods, including plenty of water and slow-release fertilizers, can produce quality top growth on minimal, even poor root systems.

Roots – out of sight but not out of mind!

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to reesermanley@shead.org. Include name, address and telephone number.