“Mulch volcanoes” are a protective ring of mulch gone mad. Heaping cones of mulch packed around the trunk of trees and shrubs and pushed right up against the bark is deadly to the health of a tree or shrub. Bark is the tree’s outermost protective layer, and needs to be exposed to air. Moisture from constantly moist, piled up mulch softens bark causing it to be susceptible to several bad actors, including:
- Wood-boring insects living in the mulch can tunnel through to the softened, partially-decomposing bark and gain easy-access to the greenwood or vascular tissues beneath the bark, introducing vectors of disease.
- Diseases such as harmful fungal canker diseases (rots), bacterial attacks or virus diseases can more easily penetrate to the interior of the plant when the bark remains continually moist.
- Critters such as mice and meadow voles can tunnel through the mulch and chew through the outer bark to reach the tasty living inner bark. This will cut off the flow of water up from the roots and nutrients down from the leaves, causing the plant to die.
- Roots tend to migrate up toward the top of the mulch layer during rainy periods, only to dry out when summer drought sets in.
- In times of drought, such a thick “volcano” of mulch a foot high can prevent rainfall or irrigation water from reaching the root system in an “umbrella” system, causing additional plant stress.
To rescue a tree from mulch death, go to this video on excavating a root collar: