Root Quality and a Durable Urban Forest.
It is literally impossible to exaggerate the importance of tree roots in the survival of individual trees and the greater durability of urban forests. Landscape tree plantings along roadways, in parking lots, or commercial/residential settings show that trees can endure, though compromised aesthetically, horrific pruning, insect damage and sun injury and remain alive. Restricted or defective root systems lead, over time, to tree death due to water stress or by wind throw. Wind throw failure also carries with it the potential for property damage and/or personal injury.
Landscape professionals are increasingly focusing on the importance of tree root health and development, from propagation to planting, in the longevity and durability of landscape trees. Three 2016 surveys, conducted by a national arboriculture web site (see link below), showed that only a limited number of wholesale tree growers, nationwide, are incorporating consistent and sophisticated methods of improved tree root structure and distribution throughout their production schemes. AZT was one of 23 nationwide nurseries that responded to the survey. In 1990, AZT began our Root Management Program, and we were encouraged to see the topic getting wider attention. Like AZT, about 40% of those who responded indicated that they had developed their individual methodologies in consultation and collaboration with arborist and other horticultural professionals.
Quoting the survey, “Growers indicated that availability was the most common complaint by nursery customers, followed by cost. Quality of root systems was pretty low down on the list of complaints.” (a) The perennial disconnect between tree availability and tree demand will forever be a part of the tree producer/buyer dynamic. The more unfortunate news is that customers under value the importance of quality roots and their role in long term survival of trees. This is a blind spot shared by portions of the landscape design, construction, and municipal entities, especially when caliper alone is a driving determinant in what tree is planted. Because trees fail, due to compromised root systems, months, years, and even decades after they are purchased and planted, the cause/effect nature of these problems are lost to the casual observer or attributed to more easily explained “recent events”. These problems go all the way back to the original tree growing practices used in the nursery and the planting methods into the landscape.
Cost and the False Equivalence: The expectation that quality productions methods may be more expensive is entirely reasonable. The survey suggests that some growers are concerned that the additional cost associated with producing quality root systems cannot be passed along to buyers in a price driven marketplace. AZT’s experience is exactly the opposite. By incorporating root quality measures, at every level of our production, and by properly training our staff, we improved the rate of tree growth which allows us to reduce our overall production time while providing a superior quality and improved tree viability. Clearly, growers need to be vigilant about labor efficiency and have good staff management, but it is our experience that trees with high quality root systems can be brought to market at competitive prices.
Relationship and Nursery Stock Growing Methods: Landscape professionals (Certified Arborists, landscape architects, municipal urban foresters, and landscape contractors) report that quality of nursery stock is the number one reason for choosing a grower, species availability is second and strong existing business relationship is third, with location and price much lower priorities.
Beyond the Grower: Projects are typically awarded to the lowest bidder, challenging contractors to be price conscious in their tree/shrub sources to offer the most competitive bid. Municipalities, landscape architects, contractors and developers need to be educated to better influence landscape tree buying habits about total quality and not just the above ground tree specifications. Root defects are a ticking time bomb for landscape projects that are only revealed years after planting. And while growers can work diligently to develop quality root structure, long term survival is also heavily impacted by planting practices and care once the tree has been installed in the landscape. The landscape design and construction community must be involved in the correction of root defects at planting time, either by doing the work themselves, training/supervising field staff, or with written specifications regarding root examination and, as needed, corrective action. Ideally, specifications for root quality could be written into the bid request or landscape plans.
Challenges: Timing is everything and it frequently works against quality landscape construction. Too often, by the time landscapes are installed, most commercial construction projects are nearing completion and there is more emphasis on finishing work quickly than doing it correctly. These conditions foster hasty purchasing decisions that rarely emphasize tree quality.
The greatest impediment to purchasing quality trees is that “no other nursery customer in my area seem to be concerned about root quality.” (a) Greater emphasis on producing trees with high quality root system will not be fully realized until the marketplace demands them. Until then, growers like AZT and others will continue to emphasize the importance of root management as part of our overall commitment to quality.
Quality Remains the Guiding Principle at Arid Zone Trees: Tree/root quality, like durability and longevity within the landscape, are no accident. Our commitment to producing premium quality desert adapted landscape trees goes back to our initial planting in 1981. Our development of clonal propagation methods that gave rise to ‘Variety AZT’ was the next step in our quest to find and grow better desert trees. The logical extension from ‘Variety AZT’, that primarily focused on the phenotypic/horticultural qualities of desert trees, was our Root Management Program that focused on producing root systems that were worthy of the trees we have selected to grow.
The Importance of Root Pruning: In sciences, like horticulture, successful repetition of an experiment is essential to establishing its credibility. AZT’s Root Management Program is the application of practices used in other aspects of landscape horticulture modified for the commercial production of desert adapted landscape trees. Our program was inspired by the extensive research conducted by Ed Gilman, Ph.D. at the University of Florida. Prof. Gilman’s work, throughout, emphasizes the critical importance of root health and distribution to the long-term vitality and durability of landscape trees. His studies focus on root development during tree production in the nursery and transplantation and maintenance practices for promoting dispersed roots for trees planted in the landscape.
Since 1999, when AZT first began evaluating and integrating root management methods into our tree production scheme, there has been an ever-increasing attention given to the importance of such practices. The most recent evidence of this has been the publications by Urban Tree Foundation (UTF). These diagrams provide instructions on how root pruning should be done. Paralleling the methods used in the AZT Root Management Program, UTF encourages the removal of a maximum of 2” of the outer edge of the rootball. This practice serves to remove any potentially circling roots and acts to stimulate the rapid development of new roots from the cut edges of more mature roots. The net result of these methods being a more rapidly growing, better distributed root systems. These methods are equally applicable, and equally important, in both bumping nursery production stock and transplanting trees into the landscape.
Certainly, there are quicker ways to bump and transplant trees, but the cost analysis is reflected in the often-used caution, “you can pay me now or pay me later.” In recent years, a focal point of our discussions about the built environment has been sustainability. Nothing is more easily managed or more critical to the durability of trees in the landscape than healthy, well distributed root systems. Production and planting practices, like those illustrated by UTF, that promote tree rooting will always pay long term dividends; environmentally and aesthetically.
a) Nurseries Speak Out On Tree Root Defects
Green Infrastructure
Root Correction Container
Correct Root Ball Shaving