Mulch around a tree should be spread like a donut, not a volcano. Never allow mulch to touch the tree’s bark, and never pile it higher than two to four inches. Mulch too deep decreases the exchange of oxygen and carbon dioxide, which can lead to fungal and bacterial diseases. The mulched area should extend, where possible, to the drip line of the branches. It is best to mulch with wood chips or other coarse organic material. For more detailed, illustrated instructions, see “Mulching Your Trees”.