If you notice green or black stains on your wood or vinyl fence, mildew or algae is likely the problem. Your fence is exposed to a lot of moisture from the elements, so it is no wonder mildew and algae may grown on it. Wood and vinyl fences that are shaded from the sun are more susceptible to mildew and algae growth. Remove mildew and algae from your fence at first sight. If left untreated, they will spread.
Fill an empty garden sprayer with one part chlorine bleach and two parts water. Swirl the sprayer around to combine the ingredients.
Spray a generous coating of the bleach solution onto the fence. Coat the entire fence with the bleach solution to maintain a uniform appearance.
Let the mixture sit on the fence for several minutes until you notice the stains disappearing. Scrub to loosen any remaining mildew or algae. If your fence is wood, use a stiff scrub brush. If the fence is vinyl, use a nonabrasive scrubbing pad.
Rinse the fence with clean water from the garden hose. Repeat this process, if necessary. Allow the fence to air dry thoroughly before staining or painting.
Wear rubber gloves, protective goggles and old clothing that covers your arms and legs when working with the bleach solution.