How Turf Impacts Tree Health
What’s your version of a perfect backyard? Most people we hear from say a sprawling, lush, healthy-looking emerald-green lawn accentuated with a perfectly located majestic tree to provide just the right amount of shade.
It’s no wonder this image is deeply ingrained in the minds of homeowners; the landscaping industry does a great job of selling this picture. But the fact is, turfgrass and trees go together like oil and water.
This is because grasses and trees are in competition for resources – like water, sunlight, and nutrients from the soil. In forest environments, trees thrive with a forest floor covered in leaf litter and organic matter, not dense grass.
In residential yards, it’s all too often a battle for survival, which inhibits both grass and trees from reaching their full potential. However, this does not mean that you can’t achieve the yard of your dreams. After all, golf courses are a great example of how grass and trees can both thrive.
Understanding the specific ways turf impacts tree health – and vice versa – is necessary for any homeowner who wants to protect their long-term landscaping design investment.
The Underground Competition for Resources
Many homeowners believe tree roots grow deep underground, but in reality the vast majority of a tree’s critical feeder roots are located in the top 6 to 24 inches of soil. This underground segment also happens to be the exact same environment occupied by the dense, fibrous root systems of turfgrass.
Therein lies the competition for water and nutrients.
Turf roots form a thick mat, making them very effective at catching and extracting water and nutrients before they can even reach the tree roots below. Recent research indicates that turfgrass is an aggressive competitor that can significantly reduce the growth rates of trees by hogging the majority of these essential resources.
Turfgrass & Trees Have Different Watering Needs
Everyone knows that proper watering is one of the most important things homeowners can do to keep their yards looking healthy, lush, and green. But what’s good for the goose is not good for the gander when it comes to turf and tree health.
Trees and lawns have fundamentally different hydration needs.
- Turf needs: Frequent, shallow watering to keep the top inch of soil moist and green.
- Tree needs: Infrequent, deep soaking that penetrates 12+ inches into the soil profile.
Problems arise when a one-size-fits-all irrigation system is set to keep a lawn healthy and green, it often keeps the soil around the base of the trees in a constant state of dampness.
This moisture can be disastrous for many tree species, particularly native evergreens like Douglas firs and cedars, which are adapted to dry summers. Excessive irrigation in the summer can lead to root rot and fungal pathogens.
This effectively drowns the trees in an attempt to save the grass. Despite this fact, with a little intentional planning and irrigation management, it is still possible to have a thick, green, lush-looking lawn combined with full, healthy tree coverage.
Mechanical Damage: “Lawn Mower Blight”
Lawn mower blight is when the blades of a lawn mower or weed trimmer string hit the base of the tree and cause injury to the tree. The area around the base of a tree, where the trunk widens at the base, is known as the “root flare.” This is where trees are particularly vulnerable, since that’s where mower blades and trimming strings come into close contact.
Repeated strikes from lawn mowers or string trimmers (aka weed whackers) can strip away the bark and damage the cambium layer beneath. The health of this layer is important for the tree’s long-term survival because it transports water and nutrients from the ground up through the trunk, branches, and leaves or needles.
Once the protective barrier of bark is compromised, wounds become entry points for decay, fungi, and insects, which can compromise the tree’s health and structural integrity over time.
Chemical Conflicts: The Dangers of “Weed and Feed”
In an effort to maintain that picture-perfect Good Housekeeping cover shot of a pristine monoculture lawn, homeowners often rely on “weed and feed” products that combine fertilizers with herbicides.
These products are designed to kill broadleaf weeds (like dandelions) while leaving the grass unharmed. All well and good for the grass, but do you know what the other broadleaf plants are in your yard?
Trees are also broadleaf plants.
While the weed-and-feed approach works for grasses, tree roots extend well beyond the canopy’s drip line and can absorb these fertilizers and herbicides from the soil. Exposure to products containing herbicides like Atrazine or 2,4-D can cause leaf curling, dieback, and significant stress to trees, as the poison intended for the weeds is taken up by the tree.
It’s akin to us drinking contaminated water.
The Problem with Artificial Turf
In an effort to reduce mowing, save water, and maintain a green lawn year-round, some homeowners turn to artificial turf. If there’s no competition with soil, shade, and nutrients, then surely this has to be the perfect balance.
While artificial turf certainly eliminates mowing and yard work, it also causes major problems for existing trees. These are the most common tree health issues resulting from artificial turf:
- Heat Island Effect: Artificial turf absorbs and radiates heat, significantly raising soil temperatures, which can bake tree roots.
- Compaction & Suffocation: The installation process often involves compacting the base layer by either manually or mechanically tamping down the subsurface. This destroys the soil’s porosity, thereby limiting the oxygen and water exchange critical for tree root survival.
- Biological Dead Zone: Synthetic turf creates a barrier that prevents organic matter (leaves and/or clippings) from decomposing and returning nutrients to the soil, effectively starving the soil ecosystem.
No matter which way you cut it, you’re probably not going to have healthy trees in a yard of artificial turf.
Tree-Friendly Alternatives
For those who want to balance the look of a lush, green lawn with tree health, there are better alternatives to traditional high-maintenance turfgrass.
Clover Lawns
Mixing clover into a lawn or using it as a primary ground cover offers several advantages for homeowners wanting the best of both worlds. Clover is nitrogen-fixing, meaning it naturally adds fertilizer to the soil rather than depleting it. It is also drought-tolerant and requires significantly less mowing than grass, which reduces the risk of mechanical damage to tree trunks.
Mulch Rings
The single best thing you can do for a tree in a lawn is to establish a mulch ring. A 2-to-4-inch layer of wood chips around the base of the tree (but kept away from the trunk itself) mimics the forest floor. This simple addition conserves moisture, moderates soil temperature, and provides a physical buffer that keeps lawn mowers at a safe distance.
Your Turf and Trees Can Thrive Together
Although trees and turf can coexist beautifully, they are not natural companions. The competition for water and nutrients, combined with the risks of mechanical damage and chemical exposure, places significant stress on trees.
But that doesn’t mean that homeowners can’t have the yard of their dreams; it just takes an understanding of fundamental plant and tree health, and a little proper previous planning.
By understanding these dynamics and maybe compromising on the size of the lawn in favor of larger mulch beds or alternative ground covers like clover, homeowners can help their trees remain healthy, safe, and valuable, curb-appealing assets for decades to come.
