Natural is a good rule. I save my grass clippings and throw them around the run. I am in Florida and anything to keep them cool is good! The leaves are great cause they love to scratch them around and lay in them. They also will hide under leafy bushes in the cool sand. If it is natural, and not an exotic plant it is okay for them. My husband loves to throw out wild bird seed every evening when he lets them out to roam for an hour or two.