The Q&A Archives: Control of Algae

Question: I have a patio paved with bricks in a shaded area. The bricks have a green/black algae growing on them that is being tracked into the house by my pets. What can a I use to kill the algae? I had the brick power washed last year but the algae just came back.

Answer: Bricks and moss or algae seem to enjoy one another's company, especially under shady, moist conditions. Power washing will remove the growth, and is the safest method to use. The chemical zinc chloride is registered for use against moss and algae on concrete, bricks and wooden decks, but it is toxic to plants, so don't use it in areas where you have desireable plants. Even diluted runoff can cause severe problems with plants several feet away from a treated area. To discourage moss from growing, sweep debris off the bricks regularly to help increase air circulation and keep the surface of the bricks as dry as possible. Expect to power wash your brick patio once a year to keep the moss and algae under control.

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