How to clean flagstone walkway?
My daughter moved into her first house and the large flagstones (Arizona flag, beige and reddish colors) make a nice, non-mortared entrance walk but they are quite dirty, sort of blackened. The same thing has happened to my flagstone patio. I tried washing with a power sprayer with no success. Is there a chemical I can use which will not destroy surrounding plants? The runoff of liquid can not be kept off of the plants.