Mildew is a type of fungus that thrives in damp or dark conditions. When mildew grows on your concrete patio, it can appear as green or black, foul-smelling patches. It can ruin the appearance of the patio, and even cause or irritate respiratory problems, according to the U.S. EPA. Clean your concrete patio with a homemade solution to kill the mildew, and keep it clean and as dry as possible to prevent future growth.
Fill a bucket with 3 qts. of warm water, 1 qt. of bleach and 1/3 cup of powdered laundry detergent. Put on rubber gloves, and stir the solution with a wooden spoon until the detergent dissolves completely.
Move any furniture, plants or items from the patio before cleaning.
Pour the solution onto the concrete patio, concentrating on areas with mildew. Allow the solution to sit for up to 15 minutes.
Scrub the patio with a stiff-bristled broom to remove any remaining mildew.
Rinse the patio thoroughly with a garden hose to remove any bleach solution. Allow the concrete patio to air dry.