Does Roundup Harm Trees? Expert Insights on Glyphosate Safety Near Woody Plants

Concerns about glyphosate (Roundup) damaging trees when sprayed underneath them are common among homeowners and landscapers. The answer isn't a simple yes or no—it depends on formulation, application technique, and tree species.

The Surfactant Factor

Research indicates that damage to woody plants often stems not from glyphosate itself, but from the surfactants (adjuvants) added to help the herbicide penetrate leaves. These surfactants can damage thin bark, especially on young trees, allowing glyphosate entry. Different manufacturers use proprietary surfactant blends, making generalizations difficult.

How Damage Occurs

Dr. Mark Czarnota, University of Georgia weed scientist, explains that injury typically results from repeated spray contact with green bark or root suckers, not soil uptake. Glyphosate binds tightly to soil particles and doesn't move laterally to tree roots. Sublethal doses cause stunting, chlorosis, bud blast, and potentially bark splitting or reduced cold hardiness—though peer-reviewed research on the latter is limited.

Safe Application Practices

• Use a shielded sprayer to prevent drift onto bark and foliage.
• Avoid spraying green bark on trees under 2 inches diameter.
• Limit repeat applications in the same zone around sensitive trees.
• Consider pre-emergent herbicides to reduce post-emergent glyphosate needs.
• Read labels carefully—most glyphosate products warn against bark contact.

Bottom Line

Glyphosate itself has low toxicity to animals and doesn't persist in soil. Tree damage is largely preventable with proper technique. When in doubt, hand-pull weeds near valuable trees or use targeted spot treatments with a paintbrush or shielded applicator.