As concern over deep roots grows, more and more established trees with deep roots are being identified in the landscape. Lack of visible root flare can be an indication of deep roots, especially if the root flare is missing on all sides. Lack of roots on just one side may be just a result of poor root development on that side. Probing with a surveyor’s chaining pin or larger tile probe can pinpoint the depth of the structural roots. If all else fails, soil excavation may be necessary.
If the roots are deeper than normal, the first question to ask is "Is the situation severe enough to require remedial action?" There is not always an clear answer. If the tree has been established for many years, and looks as good as nearby trees without deep roots, there may be no need to do anything. If a tree has symptoms of stress, such as reduced twig and leaf growth, off-color leaves, a thin crown, or dieback, deep roots may be the problem if it lacks a well-developed root flare. Be careful not to overlook other causes for these symptoms, though some may be secondary as a result of the stress that the deep roots may be causing. There is no one symptom that can conclusively diagnose a deep root problem. Actual root depth, site conditions, and species tolerance must all be considered. Above all, there is no guarantee that the tree will improve if remedial action is taken.
Short of raising the tree by transplanting, root collar excavation is the only option available to treat an established tree with deep roots. Removing the soil from around the base of the tree provides better aeration to the soil and roots. Typically, soil is removed just wide enough to expose the root flare and create a slope that will keep the soil from falling back into the excavation. Air excavation tools are fast and minimize damage to roots. The depression left by the excavation may need to be filled with another well-aerated material to avoid creating a hazard. Pea gravel is sometimes used in order to keep the base of the trunk as dry as possible. Sand and wood chips provide good aeration, but may hold too much moisture.