Causes of Mold

• Overmulching is the most common reason for the development of mold in mulch. In general, 2 to 3 inches of mulch around the base of a plant provides enough coverage to lock in moisture, block sunlight and prevent weed growth. If you apply 6 or 7 inches of mulch around the base of a plant, it prevents air circulation around the plant base and the soil and keeps excess water from evaporating, which leads to mold growth.