Using Arborist Wood Chips as Landscape Mulch

Using Arborist Wood Chips as Landscape Mulch

FS160E
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Linda Chalker-Scott, Washington State University Puyallup Research and Extension Center
Landscape mulches are important components of environmentally sustainable gardens and landscapes. Unlike soil amendments, mulches are simply materials laid on top of the soil rather than worked into it. Select the right mulch and you reap the benefits of healthier soils and plants; chose the wrong mulch and the only plants that thrive are the weeds.
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Landscape mulches are important components of environmentally sustainable gardens and landscapes. Unlike soil amendments, mulches are simply materials laid on top of the soil rather than worked into it. Select the right mulch and you reap the benefits of healthier soils and plants; choose the wrong mulch and the only plants that thrive are the weeds. This fact sheet teaches home gardeners how to use arborist wood chip mulches in their landscapes.

Benefits of Arborist Wood Chips

In areas where trees are a dominant feature of the landscape, arborist wood chips are one of the best mulch choices for trees and shrubs. Studies have found wood chips to be one of the best performers in terms of moisture retention, temperature moderation, weed control, and sustainability. In many urban areas, arborist wood chips are available free of charge (Figure 1), making them one of the most economically practical choices.

Unlike uniformly textured sawdust and bark mulches (Figure 2a), arborist wood chips include bark, wood, and often leaves (Figure 2b). The chemical and physical diversity of these materials resists the compaction often found in sawdust and bark mulches. Additionally, the materials vary in their size and decomposition rate, creating a more diverse environment that houses a diversity of microbes, insects and other organisms. A biologically diverse soil community is more resistant to environmental disturbance and will in turn support a diverse and healthy plant population.

Figure 1. Arborist wood chips are often available free of charge.
Wood chips are considered to be slow decomposers, as their tissues are rich in lignin, suberin, tannins, and other complex natural compounds. Thus, wood chips supply nutrients slowly to the system; at the same time they absorb significant amounts of water that is slowly released to the soil. It is not surprising that wood chips have been cited as superior mulches for enhanced plant productivity. Wood chips have been especially effective in helping establish trees and native plants in urban and disturbed environments.

Arborist wood chips provide substantial weed control in ornamental landscapes (Figure 3). The mechanism(s) by which wood chips prevent weed growth are not fully understood, but likely includes light reduction (preventing germination of some seeds and reducing photosynthetic ability of buried leaves), allelopathy (inhibiting seed germination), and reduced nitrogen levels at the soil-mulch interface (reducing seedling survival).

Figure 2a. Bark mulch. Figure 2b. Arborist wood chips create a diverse environment for plants.

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Copyright 2015 Washington State University

Published January, 2015

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Issued by Washington State University Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, sex, religion, age, color, creed, and national or ethnic origin; physical, mental, or sensory disability; marital status or sexual orientation; and status as a Vietnam-era or disabled veteran. Evidence of noncompliance may be reported through your local WSU Extension office. Trade names have been used to simplify information; no endorsement is intended.