by Chuck Hubbuch
Anyone who has read Tallamy’s and McCormac’s books on the importance of caterpillars in the ecosystem knows that oaks, wild cherries, maples, birch, hickories, willows and other trees are keystone species because of the large number of moths and butterflies that depend on them, along with other wildlife benefits. Specifically in our area, sugarberry and hackberry host five different butterfly species and provide small fruits for birds. Other small fruit-producing trees include hollies, tupelo, magnolias, serviceberry, mulberry, dogwood and red cedar.
Recently Upstate Native Nursery has been growing more native trees—especially species that are important for native wildlife. We’ve discovered one important trick to growing trees in containers: It is crucial that the roots of young trees develop properly. Nurseries have grown plants for sale and distribution in many different ways over the centuries. One of the oldest ways, which many nurseries still use, is to grow the plant in a field, dig it up at the time of sale, then hand the dirt and plant to the new owner. Deciduous plants can be dug in winter while they’re dormant and moved with bare roots. This method is effective but somewhat limited by the seasons and the quality of the soil in the field. Ball-and-burlap trees can be heavy and difficult to handle.
By contrast, if we grow plants in containers, the seasonal concerns and field soil quality are no longer problems. Containers provide greater protection to the roots during shipping and handling. Modern plastic nursery containers are durable, lightweight and easily transported. Unlike burlap and terracotta, the impervious surface of plastic conserves water. Transplanting from a container is possible at any time of the year, especially here in the South.
There’s one problem, though, especially with woody shrubs and trees: Growing in containers can cause roots to circle inside the pot. Trees with circling roots are considered to be root-bound or pot-bound. This is not an issue for herbaceous plants and monocots that produce new roots and shoots from their bases for their entire lives. They can recover from circling roots. But with a woody conifer or a broad-leafed plant, its young roots provide its lifelong foundation. If the roots form into a knot at a young age because they’re constrained in a container, they may never develop a natural, wide-spreading root system. It stunts their growth and may cause root girdling, whereby roots that encircle the trunk grow in diameter, effectively choke the trunk and kill the tree. Also, trees and large shrubs that are root-bound are susceptible to being blown over by storms. That’s why tall trees in small containers are not the bargains they appear to be. Pruning those circling roots when planting may solve the problem but it stunts the growth of the young tree—if it even survives the surgery.
One way nurseries can prevent this problem is to step young plants up to larger containers before the roots circle around the pot. That requires close attention by the growers, however. The best solution is to use pots that help manage this condition. At Upstate Native Nursery, we’re using tall, narrow plastic containers that encourage deep root growth. In addition to reducing the risk of root circling, this helps produce a deep-rooted sapling that will be more drought tolerant.
We expect to have a good selection of native flowering and shade trees at future Upstate SCNPS plant sales. An old adage states, “The best time to plant a tree was twenty years ago. The next best time is now.” So look for our tall pots!