I found this on the internet a while back. Note to myself…
Question: Is there a trick for growing moss on rocks to achieve a weathering effect?
Answer: When rock is brought in from outside the property to construct a rock garden from scratch, it can look out of place. Its "newness" can stick out like a sore thumb, especially if there are no signs of weathering. Growing moss would solve this weathering problem, and, believe it or not, there’s a trick for weathering rocks artificially with rock moss. It’s a job that involves strange bedfellows: namely, moss and your kitchen blender! Bring in some moss that you find growing somewhere — this will be one of the ingredients of the "recipe." Besides moss, the other ingredients will be about 2 cups of yogurt, and about 4 ounces of potter’s clay to make the moss mixture stick better to the rocks. Puree the moss, yogurt and clay until you achieve a creamy consistency. Pour the moss mixture on your rocks. As the rock moss takes hold in your rock garden, mist it to keep it moist. And voila: you have instant weathering. Nothing gives rocks that "I’ve been here an eternity" look quite like rock moss. So make growing moss a priority in your rock garden start-up activities.
