Hunker recommends a water-and-vinegar spray for algae on outdoor surfaces: start with a 10% mix, scrub the affected area and rinse. To reduce regrowth, the article advises improving water circulation and drainage, especially in damp, shaded areas.
The article's suggested starting ratio is nine parts water to one part vinegar. For heavier buildup, it says to let the solution penetrate for 15 minutes or more and notes a power washer may help. It says a 5% mix may suffice for larger areas and suggests up to 30% for vinyl siding.
Other prevention measures include running a pool filter or adding a fountain to a birdbath to keep water moving, cleaning gutters, improving drainage around low areas and removing debris that traps moisture. The guide also suggests regularly hosing down shady outdoor surfaces with a 5% to 10% vinegar solution.
