The accumulation of ivy on a structure is often considered picturesque, however, this view does not extend to moss. Moss growth on a rooftop is a problem most homeowners would like to avoid. The accumulation of moss is usually associated with shaded older roofs. It may cause problems on the roof if it is not very steep, as moss may cause moisture to back up under the shingles. Asphalt shingled roofs are normally guaranteed for 15 years. Moss usually starts showing up at the end of this period in shaded area caused by trees or buildings, or on the north side of steep roofs. The most likely cause of moss growth are trees located near the building. In addition to providing shade, the trees drop twigs, leaves, flowers, and fruits which rot and provide a place for moss spores to germinate.
The are several ways in which a homeowner can "moss proof" a dwelling, discouraging the growth of unwanted moss. Periodically sweeping the roof with a push broom with stiff bristles will help to alleviate the problem, as will spraying the roof with a strong stream of water from a garden hose or from a power washer used to clean siding.
Moss will also grow on a variety of outdoor objects. De-moss is a lasting treatment available from nurseries or from SAFER AGRO-CHEM, Jamal, CA 92035. These can be used on garden furniture, outdoor containers, and tree trunks.
Hortopics: 6/81 and 7/84. Lee Taylor, Michigan State University