How Lawn Care Products Can Harm Your Trees
- Austin Cowen
- Aug 18
- 2 min read
A healthy green lawn is a point of pride for many homeowners, but the products used to achieve that lawn can have hidden consequences for trees. Because tree roots and turf roots often overlap in the soil, fertilizers and herbicides intended for grass can end up being absorbed by your trees. Over time, this can weaken or even kill them.
Fertilizers and Salt Stress
Most synthetic fertilizers are made from mineral salts. When applied in high amounts, these salts build up in the soil and create what’s known as osmotic stress—a condition where water is pulled away from fine tree roots instead of absorbed by them.
Research from Michigan State University has shown that nitrogen fertilizers, especially ammonium-based ones, can burn roots and cause canopy thinning when overapplied. Fertilizers are rated by a “salt index,” which measures their potential to cause this kind of injury. Products with a high salt index, like certain quick-release nitrogen blends, are especially risky near trees.
Herbicides and Root Uptake
Lawn herbicides designed to kill broadleaf weeds often contain chemicals such as 2,4-D or dicamba. These compounds don’t just stay in the grass—they can be absorbed by tree roots beneath the lawn and transported into the canopy. Even small amounts can cause twisted or cupped leaves, yellowing, or abnormal growth.
Dicamba, in particular, is highly mobile in soil and has been documented by university studies to cause root injury in nearby trees. Glyphosate (the active ingredient in many common weed killers) is another concern—it moves inside plants through the phloem and can persist in tree roots long after application, interfering with normal growth processes. Symptoms may not appear immediately but can accumulate over years, slowly weakening the tree.
The Right Way to Fertilize Trees
Unlike lawns, trees require a different approach to nutrition. Tree roots extend far beyond the trunk, and their needs vary depending on soil composition, species, and age.
At NWI ArborCare, we use organic-based blends designed to improve soil health rather than overload it with salts. More importantly, we practice prescription fertilization—meaning we test your soil, evaluate the tree’s condition, and deliver exactly the nutrients it needs, in the right amounts, at the right time.
This targeted approach avoids the risks of over-fertilization, reduces chemical runoff, and strengthens the tree’s natural defenses against pests and disease. By feeding the soil and supporting the root system, prescription fertilization provides lasting benefits without the hidden damage caused by generic lawn products.
How to Protect Your Trees
Use slow-release fertilizers with a lower salt index, and apply them carefully away from tree root zones.
Avoid weed-and-feed products near trees, especially young or recently planted ones.
Create mulch rings around trees to reduce turf competition and minimize the need for chemical treatments near roots.
Monitor for warning signs such as leaf curling, canopy thinning, or premature fall color.
When to Call a Professional
If your trees show signs of stress or you’re unsure about the safety of your lawn care practices, it’s best to consult with a certified arborist. At NWI ArborCare, we provide soil testing, tree health evaluations, and treatment plans designed to support tree health without conflict from lawn care routines.
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