Tree Root Health

Clara Williams – Boxerwood Gardener

I recently attended the Mid-Atlantic Horticulture Short Course Conference in Virginia Beach, which consisted of three days of lectures ranging from basic botany to wetland restoration.  Since I have only learned horticulture through hands-on practice and self-guided research, it was stimulating to have a scholarly classroom experience.  Most of the lectures were informative and useful; however there was one lecture that was actually rather shocking.  Of course the entire lecture wasn’t all shocking, but one pivotal piece of instruction was, and when it was given, I swear I heard gasps.

Dr. Edward Gilman from the University of Florida gave the lecture entitled “Tree Care from the Ground Down.”  Dr. Gilman runs an extensive tree research program and has been studying tree systems for over 25 years with a focus on urban tree planting.  His main quest is to target the science behind what makes a healthy and strong tree, beginning in the nursery all the way to maturity in the landscape. This man knows his trees and is a self described “root nerd.”  There are two pieces of information I learned from Dr. Gilman that I want to share. The first, not so jaw-dropping, but really cool; the second, well, hold on to your gardening gloves!

Anyone who has planted a tree from a container knows that roots and plastic barriers just don’t get along.  Containers induce gnarly root girdling and wrapping, which does not help grow strong root systems. Dr. Gilman reported that the ‘shaving’ method is the best root pruning practice to correct these defects when planting. This is truly a simple method that anyone can properly do, and will undoubtedly contribute to the overall health of your tree. When planting, leave the rootball intact and place the tree in its dug hole. Take a sharp digging spade and shave off the outer ½ to 1 inch of the entire rootball, thus ‘shaving’ off the roots that are the most matted and flawed. This ensures that the severed roots will produce new growth outward, away from the rootball and horizontal to the ground surface. Leave the shaved periphery where it lies, and that’s it!

Now for what you all have been waiting for. The words that caused many arborist hearts to skip a beat: Do not mulch.  That’s right - Dr. Gilman concluded that mulching causes two major problems: it acts like a sponge, absorbing water away from the roots and therefore can cause the roots to surface to retrieve the stored water. After some concern about selling this idea to clients, Dr. Gilman seemed to reluctantly compromise with do not mulch the rootball.  If you have to mulch for whatever reason, keep it three inches or less, and leave at least a 24” mulch-free circumference around the tree base so that water can easily reach the rootball.

Spring is right around the corner, so perhaps then we can all introduce these practices into our own garden. In the meantime, visit the University of Florida’s website to read more.  http://hort.ifas.ufl.edu/woody/.