Over the past couple of decades landscapers have started a trend of over mulching trees. Although a fresh layer of mulch may look nice sometimes, you could actually be over-mulching your trees causing stress and a decrease in vigor.
“Mulch Volcanoes” is the term used when mulch is piled high directly against the trunk of trees, creating a volcano shape. They are very harmful to trees and cause many symptoms of deterioration. Mulching in this manner can even send the tree into irreversible decline.
Problems Associated with Over-Mulching Trees:
Root Suffocation/Root Rot
Deep layers of mulch cause waterlogged soil slowing water loss by preventing evaporation. To breathe, roots must have sufficient oxygen exchange.
Development of Secondary Root System
Roots navigate to the nearest available oxygen and water source. Roots buried under excessive mulch will actually begin to grow up into the mulch rather than down into the soil. This will cause roots to girdle the trunk, killing the tree.
Inner Bark (Phloem) Stress
Continuous moisture on the trunk prevents the phloem tissue from proper gas exchange, leading to poor nutrient uptake and eventually death.
Proper Tree Mulching Method
- Two-four inches (2-4") in depth
- Keep all mulch three-four inches (3-4") away from the trunk, exposing the root flare zone
- Mulch to the tree's drip line (outermost circumference of a tree canopy where water drips from and onto the ground), if possible
If a fresh look is desired each season, take some of the old mulch away before adding a new layer. Applying new mulch over old in successive years is the same as applying too deep of a layer all at once. If you have any questions about volcano mulching or tree & shrub health, post your comment below...I'd love to start up a discussion.