Learning How to Properly Mulch Can Save Your Tree

Mulches have become a standard element of most landscape plantings.  Mulches are commonly used to enhance the beauty of landscapes, suppress weeds, conserve soil moisture, and buffer plants from the damaging effects of traffic and lawn equipment.

Proper mulching is one of the best ways to promote vigorous root growth and tree health. Mulching mimics the natural environment found in forests where leaves and branches blanket the soil surface, replenishing nutrients as they decompose and creating an ideal environment for root growth.

However, excessive or improperly applied mulch can adversely affect plants. When mulch is applied too deep, piled against the trunk of the tree, or the wrong material, it can cause significant harm to trees. Besides causing the roots and stems to rot, over-mulching prevents the movement of oxygen and carbon dioxide in and out of stems; can lead to rodent chewing and stem girdling; nutrient deficiencies and the production of toxic organic acids; and often causes roots to grow up into thick mulch, only to dry out in hot summers, or form girdling roots that encircle and the trunk.

"It seems to be fashionable these days for landscapers and homeowners to create these mountainous mulch "volcanoes" at the base of trees" says Vincent Cotrone, Penn State Extension Urban Forester. "Unfortunately, this continues because there is a lack of knowledge about how trees really grow and the harm caused by this practice." A quick walk in the woods will illustrate how trees have a natural flare where their trunks meet the soil (visible even on young trees). "It is important that we not cover that flare with soil or mulch" says Cotrone. "Spread the mulch out in a layer that is no thicker than 3-4 inches, and don't pile it up on the trunks of trees and stems of shrubs".

Before you mulch your trees and shrubs this season, be sure to read the new fact sheet just released by Penn State Extension's natural resources educator Dave Jackson, entitled Mulching Landscape Trees. The fact sheet is now available on the Extension web site.