The Case for Mulch — International Society of Arboriculture

The Case for Mulch (#04)

Bert Cregg 1
  1. Horticulture, Michigan State University, East Lansing, MI, United States

Mulch has long been viewed as beneficial to trees and shrubs.  Recent research, however, suggests that the benefits of mulch may be overstated; resulting in a re-examination of mulch recommendations for trees.  For this presentation I compiled the results from three long-term (up to 8 years) field studies conducted in my lab on the impacts of mulch on survival, growth, and physiology of deciduous trees, conifers, and landscape shrubs.  In one study four types of mulch (wood chips, cypress mulch, hardwood bark and pine bark) were compared.  In the other studies, either wood chips or pine bark were used as mulch. The results of these studies show a clear and consistent pattern of significant improvement in soil moisture, plant water relations and growth when trees and shrubs were mulched compare to when they were not.  Mulch reduced weed competition and reduced soil temperature but did not affect foliar nutrient concentration (i.e., no evidence of nutrient ‘tie-up’).  The results confirm the preponderance of studies which clearly show that mulch is a critical element to maintaining healthy landscape and urban trees.