Allowing turfgrass to grow directly against a tree trunk and within its root zone is highly detrimental to the tree’s overall health and long-term survival. Arborists strongly advise against this practice because it creates a constant, low-grade conflict for resources and leaves the tree vulnerable to physical damage. The competition between the dense, shallow roots of turf and the tree’s own fine feeder roots creates a state of perpetual stress. Creating a dedicated, grass-free zone around the trunk is one of the most beneficial actions a homeowner can take for their trees.
Competition for Water and Nutrients
Turfgrass is an aggressive competitor that directly threatens a tree’s ability to absorb necessary resources. The most biologically active parts of a tree’s root system are its delicate feeder roots, which are primarily located in the top six to eighteen inches of soil. This shallow location is exactly where turfgrass develops its own dense root network, leading to a direct and intense battle for moisture and mineral nutrients. Studies have shown that turfgrass can drastically reduce the fine root density of trees in the upper soil layers.
This intense competition is particularly damaging for water, as grass is highly efficient at rapidly extracting moisture from the surface layer before it can reach deeper tree roots. When fertilizers applied to the lawn are absorbed by the grass, the tree is effectively stolen of nutrients like nitrogen that it needs for healthy growth. Resource deprivation forces the tree into a state of chronic stress, which stunts its growth rate and leaves it more susceptible to pests and diseases. Newly planted or young trees are especially vulnerable to this resource battle, often resulting in slow growth.
Physical Damage from Maintenance
Beyond the biological competition, grass growing at the base of a tree significantly increases the risk of severe mechanical injury from routine lawn care. The bark of a tree acts as a protective layer for the cambium, a thin, actively growing tissue just beneath the surface. The cambium is responsible for transporting water, minerals, and manufactured food throughout the tree, making its integrity vital for survival.
When a lawnmower is used to cut grass close to the trunk, even a minor bump can bruise or tear the bark, creating a wound that exposes the cambium. The most destructive damage often comes from string trimmers, which can easily sever the cambium layer when used to trim grass right up to the trunk. Repeated damage that circles the tree trunk is known as girdling, which completely interrupts the flow of nutrients and is almost always fatal. Even smaller wounds create entry points for wood-rotting fungi and disease-carrying insects.
Creating a Protective Tree Ring
Establishing a grass-free zone around the tree is the most effective way to eliminate these threats and promote optimal tree health. This protective area, often referred to as a mulch ring, begins by safely removing the existing turfgrass without disturbing the tree’s shallow roots. The best method involves carefully slicing the sod with a flat shovel or edging tool and peeling it away, rather than digging or tilling, which can cut fine feeder roots.
The ideal size for this ring is generous. While a minimum radius of two to three feet from the trunk is helpful, extending the ring out to the tree’s drip line offers the most benefit. Once the grass is removed, a layer of organic mulch should be uniformly applied across the entire ring. The recommended depth for this layer is two to four inches, which is thick enough to suppress weed growth, retain soil moisture, and moderate soil temperature.
The mulch provides a clear visual and physical barrier, effectively shielding the trunk from accidental contact with lawnmowers and string trimmers. However, a crucial technique is to ensure the mulch never touches the tree trunk itself. Piling mulch directly against the trunk, a mistake often called “volcano mulching,” traps moisture against the bark, encouraging decay, fungal growth, and the development of undesirable girdling roots. Instead, the mulch should be spread in a flat, donut shape, leaving a gap of several inches between the mulch and the tree’s root flare where the trunk widens at the base.