Moss is a simple form of plant growth that thrives in damp, shaded locations. It is found primarily on the north slopes of roofs and roofs shaded by over-hanging trees or nearby structures. The climate along Alaska's coastal regions provides an excellent environment for moss growth.
Moss grows well during cool periods of the year and is relatively dormant during warm weather. Moss growth uncontrolled, can damage the roof and shorten its life. Removing objects or overhanging branches that shade the roof and physically removing the moss may be necessary. Removal should be followed by applying chemicals that kill the remaining moss, and/or by placing zinc or copper strips on the roof that both kill and prevent regrowth.
MECHANICAL REMOVAL
Roof slope should be slight enough to provide excellent footing while handling removal or treatment equipment. Most home owners will be safe working on a roof with 5 feet of rise in 12 feet of horizontal run. If the roof is more steeply pitched, you should hire a contractor or someone who has equipment that allows them to do the job safely.
You may be able to remove larger clumps of moss with a stiff broom or a scraping tool of some type. Be careful not to destroy shingles when brushing or scraping. Asphalt shingles break easily in cold weather. Shake roofs become slick when wet. Removing moss prior to applying a moss killer increases control.
High pressure sprayers can be used on most roofs. Start spraying at the peak and work your way down the roof, directing the spray down the roof. Getting the high pressure spray under the shingles may result in torn shingles and water damage. In some communities, the local water pressure may be high enough to do a good job with a garden hose equipped with a small nozzle.
Galvanized zinc or copper flashing and ridges will control moss effectively for 10 to 15 feet down from the ridge on most roofs. Weathering releases zinc and copper that kills any remaining moss and prevents further moss growth. Copper wire strung every 10 feet horizontally along the butt ends of shingles provides some control. Zinc and copper flashing are available at most hardware stores. Metal ridge tops can be purchased through roofing companies or your local building supply store.
CHEMICAL CONTROL
Moss control chemicals can be purchased at most local hardware stores. The two most common active ingredients in these materials are copper and zinc.
Control is best when the moss is actively growing. In most cases, apply chemicals when rain is not expected for a few days.
Moss controlling chemicals come in liquid, granular or dust formulations. Applying liquids with a hand-held sprinkler can help reduce drift. Don't spray on windy days if you use a hose or mechanical sprayer. Some powder products are applied to the roof dry and require moisture to spread them.
Avoid applying too much solution; this prevents roof runoff onto plants below. You should cover plants below the eaves during chemical application if your house does not have rain gutters.
Copper
Copper is usually applied in the form of copper sulfate. It is corrosive to metal eave troughs, downspouts, and the metal parts of sprayer equipment. They should be flushed with water immediately after using. Unless a great deal of copper is used, it is not toxic to plants.
Zinc
Zinc is usually applied as zinc chloride. Zinc in some forms is corrosive to metal so take the same precautions as with copper. Additionally, the zinc products are toxic to plants. If you use zinc products be sure to avoid runoff onto plant areas.
APPLICATION
Before using any demossing product you need to do the following:
While using these products, be sure to:
REAPPLICATION
After physically removing some of the moss and applying a chemical treatment you will probably have a few years' reprieve from any significant moss build up. If you control new moss at early stages you will be able to use chemical controls and avoid the hard work of mechanical removal.
Some Alaskans have achieved excellent results by putting up zinc flashing after moss removal and treatment, which provides them many moss-free years.
SOURCES
Structural and Turf Demossing Study Manual, EM 4749, Cooperative Extension Service, Washington State University.
Pacific Northwest Plant Disease Control Handbook, March 1987, Page 80.
