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Controlling moss on roofs

Moss formation on roofs is a growing problem (pardon the pun). Many homes have cedar shake or shingle roofs, which are more prone to moss growth than asphalt or fiberglass shingle roofs. More people are seeking privacy by hiding their homes among the trees. And in some areas, interest in the resale value of their homes has caused the owners to try to correct years of neglect for their roofs.

Leaves or needles left on the roof from overhanging or nearby trees will retain moisture and cause moss formation. Roofs should be cleaned off periodically, using either a stiff broom or brush, or a high-pressure jet of water. Removing foreign matter from the spaces (keyways) between the individual shingles is especially important, but take care not to damage the shingles. Prune back overhanging tree limbs to allow good air movement and reduce future leaf drop on the roof.

A copper sulfate solution can also be effective when the moss is actively growing (usually in fall, winter and spring), and rain is not likely for several days. Spray it on the roof at a rate of 1/4 to 1/2 ounce per 10 gallons of water. The copper sulfate is corrosive to metal eave troughs, downspouts and metal spray equipment, so they should be washed thoroughly with water after treatment. Also prevent spray or runoff from getting onto plants you want to keep.