Under these conditions, the ground accumulates high levels of fine material as the original mulch decomposes. As additional layers are added each season to keep a fresh look, the fine layer below the visible top layer grows. The accumulation of bark fibers remains wet and seals the soil surface. Roots under a sealed surface layer are often starved for oxygen necessary for growth and development. With a weakened root system.
Foliage becomes chlorotic or small.
Stems grow weakly, and older stems may die. Well-established plants can also be injured with an overapplication of mulch piled against the stem. The injury occurs when the plant bark begins to decompose under the layer of mulch. Tree bark that is kept damp under a layer of mulch tends to respond just the same as the mulch in respect to decomposition rates. The essential connection between the food producing foliage and the nutrient and water-absorbing root system is broken.