the north face

Question: Why does moss only grow on the north side of trees?

Answer:If the tree is sufficiently shaded, moss will grow on all sides of a tree. If the tree gets a lot of sun, there is only enough shade on the north side (in the northern hemisphere) to maintain the humidity and moisture that moss needs to grow and thrive. It's not the sunlight per se, but the moisture level that determines whether and where moss will grow on a tree.