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This is second in a two-part series on mulching. Part 1 appeared in the December 2001 issue.
Chris Carlson is Director, Horticulture Technology, and Associate Professor at Kent State University, Salem Campus, Salem OH. Photo credits: Chris Carlson and Gary Watson.
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Experience and observation teach the truth in Alex Shigo’s observation: "Pruning is one of the best things an arborist can do for a tree but one of the worst things we can do to a tree." Pruning is a double-edged sword, either helping or hurting—depending on where, when, how, and why it is applied. Arborists must understand the biology of trees and how trees respond to pruning in order to optimize the health and structure of trees through pruning.
The benefits of mulching and its effectiveness in improving root development and plant vigor have been documented in scientific literature for nearly a century. Unfortunately, many landscapers, home owners, and even arborists do not fully understand when and how to properly use mulch for its positive effects on plant health and vigor. One need only look at the continued improper mounding and piling of mulch against the trunks of trees and shrubs to fully appreciate the magnitude of the problem.
Mulch truly is worth its weight in gold if selected and used properly. Research has shown that an 8-foot circle of mulch properly applied under young trees can quadruple tree root densities when compared to young trees growing with turfgrass competition and no mulch. Likewise, in mature trees, mulching has been shown to increase fine root densities up to 15 times compared to trees growing with turfgrass competition and no mulch. Research also has shown that proper mulching can reduce soil pH and relieve leaf chlorosis (yellowing), increase soil moisture, increase mycorrhizal activity, improve soil structure and drainage, and reduce soil compaction levels over time (three to five years).
Gary Watson's research illustrates the increased root density below mulch (right) compared to turfgrass cover (left)
Benefits of Proper Mulching
Most people are aware of the many benefits of mulch. Mulch reduces soil moisture loss via evaporation.
• minimizes weed competition when applied more than 2 inches deep.
• moderates extremes in surface soil temperatures.
• improves plant growth and vigor.
• reduces soil compaction and erosion.
• improves soil aeration and soil structure.
• minimizes frost heaving of small transplants.
• may increase soil fertility.
• can reduce salt buildup.
• reduces reflection and re-radiation of heat.
• reduces the incidence of some diseases.
• is aesthetically attractive.
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International Society of Arboriculture
