Who would of thought...
How to weather rocks from the Rock Garden FAQ.
Q. If I am bringing rock in from the outside to construct a rock garden from scratch, how do I hasten the growth of moss on my rocks for that weathered look?
A. Believe it or not, there's a "weathering" trick -- and it's a job for your kitchen blender! Bring in some moss that you find growing somewhere -- this will be one of the ingredients of the "recipe." Your other ingredients will be about 2 cups of yogurt, and about 4 ounces of potter's clay to make the mixture stick better to the rocks. Puree until you achieve a creamy consistency. Pour the moss mixture on your rocks. As the moss takes hold in your rock garden, mist it to keep it moist. And voila: you have instant weathering.