Moss can grow on any side of a tree, depending on various factors such as the amount of sunlight, moisture, and nutrients available. However, in general, moss tends to grow more on the north side of a tree in the Northern Hemisphere because this side receives less sunlight and stays moister, providing ideal conditions for moss growth.
But this is not a hard and fast rule, and the presence of moss on a particular side of a tree can also be influenced by other factors, such as the prevailing winds, the type of tree, and the surrounding environment.