Many books tell you that in the northern hemisphere you can find north by looking at trees on moist ground and the side of the tree on which the moss grows highest will indicate north because of the assumption that all mosses require cool, damp, shaded locations and this can often be true, but not always as you can see in the picture below. The picture was taken 1 hour after midday and the moss (on the south-easterly side of the tree) is growing about 1 metre up the tree (in this case an Ash tree).
Mosses have no roots but instead have tiny threads called rhizoids that serve to anchor the moss and to supply moisture and nutrients. Their leaves are thin and cannot retain water so instead they obtain water from rain
and dew and for this reason mosses tend to grow best in wetter places. You can learn more about mosses here.
So when using mosses on trees for navigation look at a number of trees and take an average to give a rough idea of north but not rely on it. I would also recommend getting a copy of this book “Finding Your Way Without Map or Compass” which teaches you how to recognise many natural signs and events to use for navigating.