Trees depend on a healthy root system just as much as a healthy canopy. While most people understand the importance of watering and pruning, one of the most common—and least understood—causes of tree decline happens underground: girdling roots. These hidden defects can slowly weaken and eventually kill an otherwise healthy-looking tree.
Girdling roots are roots that grow in a circular pattern around the trunk or base of a tree instead of growing outward into the soil. As both the trunk and the root increase in diameter over time, the root begins to press tightly against the trunk, restricting the flow of water, nutrients, and carbohydrates. Think of it like a boa constrictor slowly squeezing itself to death. The pressure may not be obvious at first, but over years it can have severe consequences.
Girdling roots usually develop because of planting or nursery production issues, or volcano mulching. Commonly, container grown trees are planted without having their roots corrected at the time of planting. Sometimes, the sides of the planting hole are too compacted for roots to grow into, and they start to circle the tree. Girdling roots can also form when a tree is planted too deeply. The roots will struggle to get oxygen and can grow upward toward the surface, and then cross the trunk. Once a circling root is established early in a tree’s life, it rarely corrects itself.
Trees that have been in the ground for a while can also develop girdling roots if improperly cared for. Volcano mulching trees for several years can have the same effect as being buried too deep.. Landscape fabric and weed barrier can also contribute to the development of girdling roots. When water and oxygen supplies to roots are suppressed, either by heavy layers of mulch, or by landscape fabric, the roots respond by growing upward, toward the surface, and then can circle around the base of the tree. This means that even mature trees can develop girdling roots over time.
How Girdling Roots Affect Tree Health
As both the girdling root and the trunk expand over time, this disrupts the tree’s vascular system and limits the uptake of water and nutrients. Symptoms may show up in the form of slow or stunted growth, small or discolored leaves, twig and branch dieback, or eventually, whole tree death. The reduced flow of water and nutrients weakens the tree slowly, and this can leave it more susceptible to other pest and disease issues. A weakened tree has a harder time fighting off pests.
Girdling roots can also give decay an opportunity to set in. Bark dies where the root and trunk touch, leaving the tree susceptible to pathogens. As decay sets in over time, its can spread around the base of the tree, leaving it more vulnerable to storm failures. This is why it is so important to make sure you are using property techniques for planting and mulching trees.
Girdling roots are often difficult to diagnose without excavation, since they most often exist underground and aren’t immediately visible. There are hints that can point to the presence of girdling roots. If the tree trunk goes straight into the ground like a telephone pole, with no visible root flare, this is a sign that the tree is buried too deep. If you also notice sparse, thinning, or asymmetrical canopy growth, twig or branch dieback in the upper canopy, early Fall color or leaf drop, or other signs of decline without obvious pests or disease, the tree likely has girdling roots.
Other hints to the presence of girdling roots include depressions in the trunk near the base, vertical cracking on one side of the tree, or other trunk wounding near the base. Because symptoms can take years to appear, many trees are already severely compromised by the time problems are noticed.
Can Girdling Roots Be Fixed?
There are some cases in which girdling roots can be corrected, but frequently, issues aren’t noticed until it’s too late. When caught early, ISA Certified Arborists can use an air excavator to safely remove soil around the base of the tree. This allows us to see the full root flare and buttress root system, and gives us a chance to assess and possibly correct girdling roots. If the roots are smaller, and they haven’t grafted to the trunk, girdling roots can be pruned out. This relieves the pressure on the trunk’s vascular tissues and can improve symptoms. However, every time roots are pruned, the tree needs to re-grow the portion of roots that it lost. So, follow up care and proper watering is important whenever a tree is root pruned.
Not all girdling roots can be pruned. If the roots are particularly large, or are growing deeply in the trunk, it may not possible to remove them without further damaging the tree. Further, if removing the girdling roots means removing a large portion of the whole root system, the tree may not survive the root pruning. Arborists typically don’t know what they will find until they excavate, and not every tree can be saved. Some species have a larger tendency to develop girdling roots, and some species respond to root pruning much better than others. For example, many Maples are very likely to develop girdling roots, especially if they are not planted correctly. Once Maples have been in the ground for more than 4-5 years, those girdling roots can develop so quickly that they cannot be corrected without killing the tree. Your THM ISA Certified Arborist will guide you on what the best option is for your tree.
The best approach to girdling roots is to prevent them in the first place. Proper planting, mulching, and watering is very important. Many trees already come with circling roots when you get them from the nursery.
Preventing Girdling Roots
Prevention starts at planting:
- Choose high-quality nursery stock with well-distributed roots
- Correct circling roots before planting
- Expose the root flare before planting. Trees often come from the nursery already buried too deep.
- Plant trees at the proper depth with the root flare visible.
- Loosen and spread roots outward when planting container trees
Mulch correctly to avoid future issues
- Use a coarse, organic mulch, like wood chips
- Maintain a 2-3 inch thick layer. An annual layer of mulch can often be too much.
- Keep mulch away from the tree trunk. Make sure the root flare is always visible. Mulch is beneficial for the roots, not for the base of the tree.
- Avoid use of landscape fabric and weed barriers.
- Expand the mulched area as the tree grows. A larger area is always better.
Healthy roots support healthy trees, and trouble in the root system can shorten a tree’s life. If you are interested in planting a tree, or are concerned that one of your trees is struggling with girdling roots, reach out to Tree Health Management for a consultation from an ISA Certified Arborist.