From Janet H.:

This is a great tip for barns or sheds that have shingles on the roof that have moss starting to grow on them. To get rid of the moss and keep it away for several years, apply baking soda fairly heavily, making the roof appear whitish. Leave it there and watch the moss disappear. It may take some time to work. The baking soda soaks into the shingles and changes the pH, making it inhospitable for the moss. You can also use this trick on wooden decks and concrete porches, patios, and steps. You may want to use a sifter to apply the baking soda more evenly.

Majestic Duke owned by Kelli Hewitt  

http://www.pintabians.org/ranch