Over-mulching can be dangerous

Over-Mulching Can Kill Your Plants

Over-mulching can be dangerous.

A recent and serious trend has been over-mulching landscape plants. Although a fresh layer of mulch may look nice, you could be using too much mulch.  Mulch volcanoes is the term used when mulch is piled high directly against the plant trunks, creating a volcano shape.  This can cause stress and deterioration of the plants. Here are a few problems caused by over-mulching plants.


Root Suffocation

Suffocation of plant roots is a common cause of stress.  When too much mulch covers the soil surface, air cannot get through the mulch layer and the underlying soil becomes depleted of oxygen.  Also, deep mulch can slow water loss through evaporation promoting waterlogged soil and root zone. Roots must take in oxygen to stay healthy.  When soil oxygen levels drop too low, plants cannot absorb water and nutrients causing root growth to diminish.  If too many roots diminish the plant can die.

Secondary Root System Develops

Roots navigate to the closest water and oxygen source. Roots buried under excessive mulch will 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 Death

Phloem is the inner bark that carries photosynthates produced by the leaves to the rest of the tree. Root flare and trunk tissues stay constantly wet when covered by too much mulch. Continuous moisture limits oxygen and carbon dioxide gas exchange between living cells in the trunk and the atmosphere. If wet conditions are prolonged, phloem tissue will die, and roots are starved of essential carbohydrates.


The wet, decaying moisture from piling the mulch next to the trunk can allow fungal and bacterial diseases to grow and reproduce.  Once established, the disease can starve the roots and kill the plant.

These are a few reasons why it is important not to over-mulch.  Call Integrity Tree Care today to evaluate your landscape.

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