We have all heard that moss grows on the north side of a tree right? And if we get lost on the woods, we should look for moss to find north and hopefully, our way home. True or folk lore?
Well, moss will grow on the north side of a tree because it is more shady in summer, thus retaining more moisture. However, moss will also grow on the south, east and west side of trees as well. Mosses are primitive plants with no roots, stems, or leaves. Instead, they have large colorless hollow cells which allow them to absorb water and hold it like a sponge. In the dry summer, you find brown dry moss, but as soon as it rains, the moss plumps up and turns green again.
Mosses need a lot of water for two reasons. One is that they’re not “vascular” plants–that means that they don’t have the plant version of a circulatory system, and they can’t move water around inside their bodies. All cells in a moss’ body need to have easy access to water from the environment. The second reason they need water is because their male reproductive cells can only survive by swimming in droplets of water. The only way these cells can get from one plant to another is to hope that a raindrop will cause the water they’re swimming in to be splashed onto a neighboring plant. If the surface that they live on (like a tree trunk) dries out, the moss will be unable to reproduce, and it will dry out. That’s much more likely to happen on the sunnier side of a tree trunk than on the shadier side.
As I walked down the muddy paths today, enjoying the rare January sunshine, I noticed that many of the trees near Little Huckleberry Creek had bright green moss growing on the south side of the trunks. In winter, the sun doesn’t give as much energy as it does in the summer, so the moss is going for the most solar energy it can find – on the south side of the trees. Since it rained recently, and the sun is out, the green chlorophyll went into action to generate some food for the moss while the conditions are just right! Let’s go back next summer and see if the moss still grows on the south side of those trees!