The sight of moss growing on a roof lends a house a romantic, old-fashioned air, but the moss can lead to leaks and structural damage. Apply copper sulfate to a roof to kill moss and limit regrowth.
Copper sulfate kills moss on contact, making it ideal for killing moss growing on your roof. If the moss is growing in thin layers, spraying it with a copper sulfate solution kills it right away, and the dead moss can easily be washed off the roof with a hose or pressure washer.
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To kill moss, add half an ounce of copper sulfate to 10 gallons of water. Mix thoroughly, and then wet the problem moss with the solution. Allow it to sit for 10 to 20 minutes, and then rinse the solution off the roof with water. The rinsing action should carry most of the moss off the roof, although you could need to sweep some patches off with a broom.
You can use copper sulfate yearly on the roof to get rid of moss. It has a good residual effect and will provide some protection against new growth. To prevent moss from growing at all, install copper strips along the top of the roof and run copper wires along the length of your roof every 10 feet below the top strip. The copper emits ions during each rainfall that inhibit future moss growth.