When a Tree Goes Too Deep
Trees can be planted too deep and the culprit is typically our over-caring urges to protect them. We want to ensure the tree is anchored solidly and is well braced so we think that planting it deeply accomplishes this. But more often than not you’d be wrong. Even professionals can make the mistake; one recent study suggests that 93% of professionally planted trees are planted too deep.
When tree roots are planted too far underground, secondary roots grow toward the surface to compensate. Rather than growing up and then out from the tree, they often encircle the trunk (called “girdling roots”) and ultimately choke it out. It can also cause bark on the trunk to start falling off and make the tree more susceptible to disease and pests.
This peeling bark on the base of the trunk was the first sign that our two Emperor I Japanese Maples (Acer palmatum) had been planted too deep. The mulch had hugged the trunk bark for so long that it choked off oxygen and caused the protective bark to peel off. For our second identical tree I cleared away the top few inches of soil and exposed the root flare. In the second photo above you can see below the T-bud swell and the beginnings of girdling roots.
If the dangerous wounds don’t kill the tree, the girdling roots just under the mulch would eventually suffocate it. The early sign of peeling bark was actually fortunate for us. For most trees planting them too deep doesn’t have much effect until about 10 to 20 years later when the girdling roots choke the underground trunk like a noose.
No matter what form of tree you choose to plant, whether balled-and-burlaped, container-grown, or bare-root, the key is to determine where the topmost root (called the root flare) is growing off the trunk. You then have to ensure that the root flare is at (or ideally just above) the soil grade of the planting site.
Since mine were already planted I had the tough task of actually raising the trees. Fortunately Japanese Maples have notoriously compact root systems that make them easy to uproot and move. Mine had also only been planted about nine months ago so the root system wasn’t that extensive.
With the help of my father I carefully dug a ring around the trees and lifted them up, adding a thick layer of new tree-friendly soil beneath them until the tree collar was slightly above the ground line. Extra roots on top of the soil should eventually be removed, and then a thin layer of mulch added over it. This time I’ll be sure to keep the root collar above ground and prevent mulch from hugging the trunk. The final product below shows healthy trees that should thrive for decades to come.