(HIT)- Mulching is one of the most beneficial things a homeowner can do to keep trees healthy. It makes growing situations more “friendly” for trees in general. But over-mulching can be one of the worst landscaping mistakes you can make, causing significant damage to trees and other plants.
“All things in moderation should be a homeowner’s mulching motto,” says Jim Skiera, Executive Director of the International Society of Arboriculture (ISA). “As beneficial as mulch is, too much can be harmful in more ways than one.”
|Improper technique – Fredric Miller, Joliet Junior College, Bugwood.org|
The generally recommended mulching depth is two to four inches, according to the ISA. When applied properly, mulch helps maintain soil moisture, control weeds, improve soil structure, and inhibit certain plant diseases. Mulch also protects plants and trees from “weed whacker” damage and “lawnmower blight” in addition to giving planting beds a uniform, well-cared for look.
But too much mulch-be it layers deep or piled high against tree trunks-can cause major problems for homeowners, including:
- Excess moisture in the root zone, which causes plant stress and root rot
- Insect and disease problems
- Micro-nutrient deficiency or toxicity
- Weed growth
- Smelly planting beds, caused by anaerobic conditions and “sour” mulch
- Habitat creation for rodents that chew bark and girdle trees
Why mulch at all?
Urban landscapes are typically harsh environments with poor soil conditions, little organic matter, and big fluctuations in temperature and moisture – all “unfriendly” growing situations for trees. A two to four inch layer of organic mulch can mimic a more natural environment for trees and improve overall plant health.
When mulching, Skiera says it is important to remember that the root system of a tree is not a mirror image of its top. “The roots of most trees extend out a significant distance from the trunk. Also, most of the fine absorbing roots of trees are located within inches of the soil surface.”
|Proper technique – Joseph O’Brien, USDA Forest Service, Bugwood.org|
These shallow roots are essential for taking up water and minerals for trees, and they require oxygen to survive, Skiera says. A thin layer of mulch, applied as broadly as practical, can improve the soil structure, oxygen levels, temperature, and moisture availability where these roots grow.
To ensure the health of your trees and plants, follow these practical mulching tips to landscape like the pros:
- For well-drained sites, apply a two to four inch layer of mulch. If drainage problems exist, use a thinner layer.
- If mulch is already present, check the depth. Do not add mulch if there is already a sufficient layer (2 to 4 inches) in place. Instead, rake the old mulch to break up any matted layers and refresh the appearance.
- 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 out to the tree’s drip line or beyond if possible.
- Most commonly available mulches work well in most landscapes. Be mindful of the fact that some plants may benefit from the use of a slightly acidifying mulch such as pine bark.
- Organic mulches are preferable for their soil-enhancing properties. Be sure it is well aerated and composted to avoid sour-smelling mulch.
- Avoid using uncomposted wood chips that have been piled deeply without exposure to oxygen. Use composted wood chips instead, especially when they contain a blend of leaves, bark, and wood.
The International Society of Arboriculture (ISA), headquartered in Champaign, Ill., is a nonprofit organization supporting tree care research around the world. As part of ISA’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, or to find an ISA Certified Arborist, visit www.isa-arbor.com.