Root flare
Root flare
The Maine Department of Agriculture, Conservation and Forestry recently issued tips for properly mulching trees, as spring yard work time has arrived. Mulching can benefit trees, but improper techniques can hurt or even kill them.

The benefits of properly mulching landscape trees with organic material, such as bark or wood chips, is well known. Mulch inhibits weeds, helps retain soil moisture, enriches the soil as it decomposes and may moderate soil temperatures. Perhaps even more importantly, a circle of mulch around a tree can help protect it from errant lawnmowers and string trimmers. However, a little goes a long way.

“Volcano” mulching is an improper tree care technique in which mulch is piled against the trunk of a tree year after year. Properly planted trees (or naturally grown trees) will develop a characteristic root flare near ground level. Volcano mulch buries the root flare or, in young trees, prevents a proper flare from ever developing. Trees without proper root flare lack stability and are more prone to windthrow. Mulch piled against a tree’s stem also encourages disease and decay because the bark is almost always wet. Huge piles of mulch also interfere with good root development — if the top few inches of soil are always moist, roots may not spread deeply into the soil, leaving trees high and dry during a summer drought.

To mulch properly, spread a layer of mulch two to four inches thick under trees, making sure that no mulch touches the trunk. For younger or newly planted trees, spread mulch out to the dripline (the outermost part of the tree’s canopy where water drips onto the ground). For older, well-established trees, try the “3-3-3 Rule”: Spread a three-inch layer of mulch in a three-foot donut around the tree, making sure to leave at least three inches between the mulch and tree stem.