Use a broom to remove any loose dirt. Rinse using a garden hose to wash off mud. Scrubbing the rocks with vinegar and a scrub brush will remove algae and moss. Re-rinse rocks after scrubbing with a garden hose.
Hose off and scrub medium to large landscape rocks with a nylon, stiff-bristle brush. Use plain water and rinse the area well when finished. This is an excellent way to remove caked-on mud and bird droppings. Add a squirt of two of dish detergent to your bucket of water to help remove stubborn stains or dirt.