Moss on asphalt shingle roof
I have moss growing on north facing parts of my asphalt shingle roof. There are no nearby trees to prune. Most searches say do not scrape or brush it off since it damages the shingles. They recommend 50/50 treatment with bleach and water. I'd like to find a product which will leave a residual on the shingles which will last for a while, so I do not have to repeat the bleach treatment very often. Any suggestions?
Montgomery County Maryland
We do not know of a product with residual properties.
Here is an old article (1962) from Google Scholar on the subject. Most of the chemical approaches mentioned cannot be used today but the copper sulfate seems to be ok and may leave some residual.
There is a page published by Oregon State on moss control on roofs, which overviews the potential pros and cons of several treatments: http://bryophytes.science.oregonstate.edu/page24.htm. The risk-benefit analysis is best left up to you regarding the costs of treatments, ease of treatments, and risk of damage to existing landscaping from any contaminated water runoff. We do not have any specific information regarding preventing moss growth on roofs in our region, nor do we have data on if moss damages the shingles.