Damp, shady areas of the yard provide ideal conditions for moss to grow on tree trunks, the ground and even stepping stones. While moss can be attractive in some situations, moss on stepping stones makes them slippery and treacherous. You can remove the moss, but if the conditions that foster it persist you may have to make the cleaning a regular chore, as the moss is likely to return. Stepping stones are usually set in the midst of grass, flowers or other desirable plantings, so when you clean them be careful not to harm the plants.
Spread heavy plastic on either side of the stones to protect surrounding vegetation. If your stones are a uniform shape or size, use scissors to cut out a hole for one stone to poke through. Move the plastic as you clean one stone at a time.
Connect the power washer to a water hose, then plug the extension cord into an outlet. Turn on the water and switch on the power washer.
Compressing the trigger on the power washer handle, aim the nozzle at the stepping stone. Direct the water in a sweeping motion back and forth across the stone, blasting away the moss. Work slowly and carefully, cleaning one stone at a time.
Scrub away any moss still clinging to the stone with the scrub brush. Rinse with the power washer or water hose.