Nursery Standards – Rootstock Problems and Specification

Roots properly pruned with no roots above the root collar Photo credit: James Urban

Roots properly pruned with no roots above the root collar
Photo credit: James Urban

Stem girdling roots, kinked roots, J roots, T roots, and root collars buried deeply in the root package are one of the principle reasons whey trees and large shrubs fail to recover from transplanting or decline and even die at a young age after planting. These problems are typically created in the nursery by practices that do not produce plants with radial root architecture and place the root collar close to the surface of the soil. As a plant moves thru the production process from propagation to delivery at the site, there are many opportunities for root problems to develop in the plant.

Most plants are started in small containers and then gradually moved into larger containers. If the plant is sold in a container there may be three or four different container sizes. Each of these containers may result in a series of roots circling around the edges of the pot forming circling roots. Any of the circling roots above the root color can eventually choke the tree. Other roots may be deflected from the bottom of the container and grow upward to the surface forming a sharp kink in a root that may eventually become an important structural root. If these misshapen roots are not pruned at each shift in pot size they form an imprint of constricting roots in the next container. As trees are repotted they are also often placed too deeply in the next pot. Trees lined in the field may also be buried in the soil. This places the roots too deep in the soil where oxygen is less available at a critical point in the trees development.

Circling roots that lacked root pruning during tree production Photo credit: James Urban

Circling roots that lacked root pruning during tree production
Photo credit: James Urban

Emerging research is documenting these problems and offering solutions. Better nurseries are changing their production process to reduce root conflicts. Independent groups are re-writing specifications and planting procedures that acknowledge and solve these problems. This entry is intended to gather existing research, organize a discussion to better understand the problem, and help form a mutual understanding between growers, contractors and landscape architects. It is hoped that the result will be better quality plants for the industry.

References

Urban Tree Foundation, Visalia, CA  93292  Specifications and planting details.

University of Florida, Gainesville Florida 32611  Research on tree production, and transplanting.

Illinois Green Industry Association, Springfield IL Details and Standards for tree specifications

American Hort, Columbus, OH.  ANSI Z60.1 The American Standard for Nursery Stock 2014

Author
James Urban, FASLA, Jimtree123@gmail.com