Root Pruning Potbound Plants

Fall is a great time to buy trees and shrubs at your local nursery. Most gardeners have heard that if your tree or shrub is potbound (roots encircling the rootball), you should score or break up those roots before planting.

Now research from the University of Minnesota indicates that this procedure may not be necessary. Researchers planted potbound linden and willow trees into test plots. Before planting, some of the trees' rootballs were scored (1-inch-deep cuts were made into the rootball), butterflied (rootball was cut in half), or teased (roots were hand pulled so they faced outward) to break up the circling roots. The control group was planted without any treatments. After two growing seasons the researchers dug up all the trees and recorded the numbers and sizes of the roots. Researchers found that none of the methods of breaking up the potbound roots prior to planting increased the size or number of roots, or the ability of the roots to grow into the native soil.

They concluded that any roots encircling the plant above the root flare (base of the tree) should be removed since they may strangle the tree trunk as they grow. However, those below the root flare should be left as is, and they will naturally grow out into the native soil.