Common Landscape Pitfalls: Tree Root Problems
See our article Planting and Establishing Trees for more details.
It is easy to assume that a slow growing or struggling tree just needs a little extra care. Unfortunately, root problems below ground are often instead the culprit. All the proper pruning, watering, and fertilizer in the world won't make up for poor root health.
This article covers a few common root-related problems. While homeowners and landscapers can fix some of these issues on their own, a problem with the roots puts the entire tree at risk. For this reason, we suggest you call a certified arborist in to assess the safety of your tree. Tree failure resulting in injury is uncommon, but it's better to be safe than sorry.
Tree Planted Too Deeply
Incorrect planting depth is probably the most common cause of root-related issues. Most trees have a well-defined root "flare" that you should see above the ground. If the tree is planted too deeply, or if the root flare is covered with soil, the entire tree will suffer.
Roots require air as well as water. Roots planted too deeply often lack oxygen. They may also end up receiving too much or too little water, depending on the site. Often the tree will not die immediately. Instead, it may grow very slowly for years before failing. Circling roots, reaching toward the surface, can make the situation worse. As the tree grows, these roots grow around the trunk, becoming tighter and tighter. Eventually they will "girdle" the tree (more on this issue below).
If the root flare of your tree is not above the soil surface, you may still be able to save the tree. The best option is to dig up the tree and re-plant it at the correct depth. With larger trees this may not be possible. If the tree is large and planted only a few inches too deep, you may be able to remove the soil on top and expose the topmost roots. As you do this, remove any roots you find crossing main roots or circling the tree.
Girdling/Circling Roots
Even if the tree is planted correctly, roots growing above the surface can cause problems. Trees grown in containers often have roots that grow in a circle, running along the container's inner wall. These circling roots will tighten around the base of the tree as it grows. We call this girdling, and it is dangerous to your tree's health.
A tree stump showing signs of root problems: girdling roots and the resulting rot. Credit: Madeline Iyer, UF/IFAS.
Girdling is easy to avoid early on. At planting time, shave off the outer inch of the tree's root ball with a sharp shovel or handsaw. This removes most roots that could eventually strangle the trunk. It also encourages roots to grow quickly into the landscape soil and makes the tree sturdier in winds.
After planting, girdling is harder to fix. If the girdling root diameter is less than 25% of the tree trunk diameter (measured 4.5 feet above ground) it is safe to cut and remove root. If you cannot do this without damaging the trunk, you can completely sever the root but leave it in place. If the root is larger than 25% of the trunk diameter, removing it may not be possible. We suggest consulting a licensed arborist to decide if the tree can be saved.
Root Damage Due to Heavy Traffic
Another common root problem is damage resulting from soil compaction. A tree's root zone is wide and shallow. It is shaped more like the base of a wine glass than a reflection of the branches above. Imagine a carpet of roots, just below the surface, extending out beyond the drip line.
Densely packed soil is difficult for roots to penetrate, and is often starved of water and oxygen. These conditions aren't ideal for any tree but some trees are particularly sensitive to soil compaction. Sensitive trees include sweetgum (Liquidambar), dogwood (Benthamidia spp.), sassafras (Sassafras spp.), tupelo (Nyssa spp.), pine (Pinus spp.), white oak (Quercus alba), laurel oak (Quercus laurifolia) and most nut trees, such as black walnut (Juglans nigra), hickory (Carya spp.), and pecan (Carya illinoinensis).
Protecting the area beneath a tree's drip line is the best way to protect the roots below. Driving over the root zone with a car can press the soil down and damage the roots. If you're parking cars under a tree canopy, the chances are the area is highly compacted. Even regular foot traffic can be a problem. Digging up the area to install a hardscape, like a patio, can do damage, too.
Happily, you can remedy compacted easily with an AirSpade or Supersonic Air Knife. These tools blast air into the soil, loosening it without cutting the roots. It won't reverse existing damage to the roots, but new roots can quickly grow into the looser soil. Protect the root zone in the future and your tree will thrive.
If new construction makes some traffic over the rootzone unavoidable, you can still protect the roots. Spread a 12-inch layer of coarse bark mulch under the canopy. Cover this with steel plates. Vehicles can drive on the plates without damaging the tree roots below. Once the construction is finished, remove the plates. Spread the mulch around to a depth of three inches, keeping it well away from the trunk.
Other Root Issues
Even foot traffic can compact soil. Credit: UF/IFAS
Be on the lookout for other clues that you might have root issues. Visible cavities or swellings in the root collar are never a good sign. Fungal growths around the base of the tree may indicate decay as well. Remember, any issue affecting the roots can destabilize the entire tree. If you suspect root problems, call a certified arborist in to assess the safety of your tree.
More information about tree root problems and solutions can be found on the Landscape Plants website from Edward F. Gilman and the UF/IFAS Environmental Horticulture Department.
For more information about root-related tree problems contact your county Extension office.