Why Is Grass Growing Right Up Against My Tree a Problem?
Turf competes for water and makes mower or trimmer injury much more likely. A proper mulch ring gives the tree safer ground.
Grass against a trunk is not an emergency, but it creates two persistent problems: turf and tree roots compete for the same water and nutrients, and every mowing brings equipment close to living bark.
CSU reports substantially more fine root-hair development under mulch than under grass. For recently planted trees, CSU also notes better growth where a mulch ring replaces turf near the trunk.
The damage you can see—and the competition you cannot
String-trimmer scars and mower impacts can damage the tissues that move water and sugars through the tree. Repeated injury at the same height can eventually girdle a young trunk. Underground, dense turf roots occupy the upper soil where many tree absorbing roots also grow.
A mulch ring removes the need to trim against bark, reduces evaporation, moderates soil temperature, and makes irrigation easier to direct across the rooting area. Wider is generally more useful than deeper.
Build a flat ring, not a volcano
- Remove or suppress turf carefully without cutting major tree roots.
- Use wood chips or another suitable organic mulch over a broad area.
- Keep mulch at least six inches away from the trunk and preserve the visible root flare.
- Maintain the intended depth; piling new mulch on old mulch reduces oxygen and can keep bark wet.
A Colorado Springs exception
Organic mulch can be combustible. In wildfire-conscious landscapes, especially immediately beside a structure, material choice and spacing should follow current defensible-space guidance. A tree can still have a protected, turf-free rooting area without carrying loose woody fuel against the house.
Sources & further reading
These Field Notes translate Colorado horticultural guidance into practical homeowner language. For the underlying recommendations, start with the original CSU Extension resources: