Moss loves shade and wet areas. Moss is easily controlled. Moss Control products for plants contain a natural iron compound which not only kills moss but turns grass and leaves dark green. Iron compounds can stain concrete a rust color. So if some is spilled on concrete, brush it off before it becomes wet. (I have had some success removing rust stains on concrete with “Lightning Rust Remover”.) Many fertilizers contain iron. A minimum of 5% iron is necessary for moss control. Moss Out for Roofs and Structures contains a natural zinc compound which is non-staining and non-corrosive to wood, concrete, asphalt and metal.