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Mulch -- not just for looks          Send a link to a friend

[JUNE 23, 2006]  CHAMPAIGN -- Many homeowners choose to mulch because they enjoy the well-cared-for look it gives their landscape. But, they may not realize they are also providing many benefits for their trees. With mulch, the result can be a better growing environment for trees and their roots.

Homeowners should be aware that, generally, the root system of a tree spreads out, not down. "The roots of most trees extend out a significant distance from the trunk. Most of the fine, absorbing roots of trees are located within inches of the soil surface," says Jim Skiera, executive director of the International Society of Arboriculture. These shallow roots are essential for taking up water and minerals for trees, and they require oxygen to survive. A thin layer of mulch, spread widely, can provide a healthier environment where these roots grow.

Mulch benefits

Properly applied mulch provides many benefits to the health of a tree. Unlike trees growing in a forested environment, urban trees are not typically planted in an optimal environment for root growth and mineral uptake. Typically, urban environments are harsher, with poor soil conditions and large fluctuations in moisture and temperature. Applying mulch can help reduce the stress of such conditions through these benefits:

  • Helping to maintain soil moisture with less evaporation.

  • Reducing the number of weeds.

  • Providing insulation by keeping soil cooler in the summer and warmer in the winter.

  • Protecting from damage caused by lawn equipment such as Weed Eaters and lawn mowers.

  • Improving soil fertility, aeration and drainage.

Organic or inorganic

Mulches are either organic or inorganic material mixtures that are placed over the soil surface around the base of a tree. Mixtures consisting of various types of stone, rock, pulverized rubber and other materials are labeled as inorganic. Because these types of mixtures do not decompose, they need replenishing less often. However, this also means they do not improve soil structure, provide nutrients or add organic materials to the soil. Inorganic mulches do still provide other benefits, such as insulation and protection.

Organic mulches consist of wood chips, pine needles, bark, leaves and other products derived from plants. These mulches decompose; thus, they are very beneficial in improving soil quality by replenishing nutrients. They do, however, require more maintenance because decomposition creates the need to replenish more often.

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Mulching dos and don'ts

In order for mulch to be beneficial, it must be applied correctly. "'All things in moderation' should be a homeowner's mulching motto," says Skiera. "As beneficial as mulch is, too much can be harmful in more ways than one." Too much mulch can create excess moisture that may lead to root rot. Other problems created by over-mulching include insect and disease problems, weed growth, sour-smelling planting beds, and chewing rodents.

To ensure the health of your trees and plants, follow these practical mulching tips to landscape like the pros:

  • Thin is better. Apply a 2- to 4-inch layer of mulch unless a drainage problem exists; then a thinner layer is recommended. Do not add mulch if there is already a sufficient layer; instead, rake the old mulch to break up any matted layers and refresh the appearance.

  • No volcano mulching. Avoid placing mulch against the tree trunks. If mulch is already piled against the stems or tree trunks, pull it back several inches so that the base of the trunk and the root crown are exposed.

  • Mulch wide. Mulch out to the tree's drip line or beyond if possible.

The International Society of Arboriculture, headquartered in Champaign, is a nonprofit organization supporting tree care research and education around the world. As part of the society's dedication to the care and preservation of shade and ornamental trees, it offers the only internationally recognized certification program in the industry. For more information and to find a local ISA-certified arborist, visit

[International Society of Arboriculture news release]

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