Using mulch around the base of plants has many benefits including retention of soil moisture and prevention of heat loss. However, when applying mulch, one should be careful not to use too much, checking to see that it is not smothering the base of plantings and is not more than four inches high in the beds. The key symptoms that indicate over-mulching are off-color foliage, small leaves, poor twig growth and tieback of older branches. Over-mulching can cause many problems, if not corrected in a timely manner, including root oxygen starvation, inner bark death, disease and insect promotion, and chewing rodent harborage.
Trimming keeps all of your plantings in a manageable and healthy state.