A tree’s root collar is the transition area from the roots to the trunk. It is usually noticeable because of the prominent flare leading to the major buttress roots. Trees should have this visible flare where the roots curve out of the ground. On the other hand, trees that seem to grow straight from the ground (like telephone poles) are a red flag of tree root collar disorders.
The root collar is considered ‘buried’ under soil or mulch when a tree is planted too deeply or when excessive mulch is piled against the trunk. Improper planting is a likely cause so be sure to follow proper tree planting tips. Volcano mulching, where mulch mounds surround the trunk, is another frequent culprit.
Buried root collars are a common and serious issue. The bark in this area is actually more trunk-like than root-like. While a tree’s roots are able to tolerate high levels of soil moisture, the root collar is not. When buried, the root collar remains damp and moist inviting numerous problems.
Damage to the bark on the root call can interfere with the downward movement of food (photosynthates) to the roots and inhibit the movement of oxygen and carbon dioxide. Ultimately, this can lead to root dieback, reduced water uptake and, possibly, tree death.
Also, root collars with damaged bark are more susceptible to infection and disease. Moreover, for some tree species, a buried root collar can lead to girdling roots. This is when roots circle the trunk and eventually strangle the tree.
Symptoms of Tree Root Collar Disorders
When the root flare is not visible, it is important to excavate and examine the bark and and sapwood for signs of infection. Beyond the bark and sapwood in the root collar area, there are other symptoms. Foliage yellowing, early leaf coloration and drop, and dieback in the upper crown can indicate root collar disorders.
Treatments to Improve Tree Health
Remedial action can often be taken if the tree is not severely declining from a root collar disorder or root decay.
- First: Remove excess soil or mulch that is covering the root collar. Root collar excavations should be done carefully with small digging tools and a brush. A high-pressure air tool such as the AirSpade is an excellent alternative to remove soil without causing further injury to the tree.
- Second: Carefully prune out any stem girdling roots.
- Third: Fertilize based on a soil analysis.
- Fourth: Be sure to irrigate during dry periods. Do not apply water directly to the trunk or root collar area and be careful not to overwater.