Proper Tree Planting Depth
June 2, 2016
Good tree planting procedures are the key to giving trees a healthy start. One of the most common problems we find with newly planted trees when we are out doing tree inspections with clients is improper planting depth, specifically trees that are planted too deep. Planting trees too deep is a major concern because most of the roots that provide the tree with water and nutrients are located in the top six inches of soil. If a tree is planted too deep, oxygen exchange is diminished and roots begin to suffocate resulting in root dieback followed by corresponding branch dieback in the above ground branches.
Some species of trees may develop roots in the upper layers of soil to find more oxygen, but often times these roots lose their normal outward orientation and begin wrapping around the trunk or root collar creating stem girdling roots. Stem girdling roots compress the layer of tissue just beneath the bark, cutting off the flow of water and nutrients. This leads to dieback in the top of the tree and possible tree death over time. Tree species especially prone to stem girdling roots include maple, linden, ash, and crabapple.
To prevent stem girdling roots, inspect all containerized and balled and burlapped trees before planting. Look for the root flare (the widening out at the base of the tree) and the first branching root. Remove any additional soil above this point after the tree is in the planting hole. Make sure this first branching root is at or slightly above the original soil grade before backfilling the planting hole. Also, inspect the root system for any roots that may be growing against the stem and remove these roots before planting.
After the tree has been planted, do NOT mound mulch against the stem of the tree. This is the same as planting too deep. Random inspections for early signs of encircling roots are recommended after planting. These inspections are done by root collar excavations using the Airspade, which utilizes compressed air to excavate the soil around the stem without damaging roots.
If encircling roots are found, prune them out before they contact the stem and cause compression. If compression of the stem has already occurred, treatment depends on the severity of the compression. Often the compressing roots can be cut or chiseled away to provide relief. Depending on the size of the roots removed, additional stress may be incurred for the short term until the tree can replace some of the roots removed.