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What's This Green Stuff Growing on my Trees and Rocks

Himni Palacios
Content Contributor

Are leaves not the only green thing growing and living on your trees? If you're wondering what that might be, the answer to your question is moss and lichen.

You'll Be Lichen This Article | Field Station

What is Lichen?

Lichen looks much like a plant but is actually a fungus. Lichen can grow on many surfaces from trees to concrete, and even metal poles. Lichen can only exist if there is a cyanobacteria (tiny organisms of blue-green algae), present. The lichen and algae have a symbiotic relationship, the algae providing photosynthetic energy while the lichen provides protection. The algae make energy through the process of photosynthesis, and the fungus provides protection from the elements to the algae. Lichen reproduce through the production of spores as with other fungi, or when pieces of bark fall on the appropriate terrain.

Myth Buster: Moss Doesn't Only Grow On The North Side of Trees - Forest  Preserve District of Will County

What is Moss?

Moss is not only a plant, but it is one of the most primitive plants, with a simple structure that has remained largely unchanged over the course of millions of years. Unlike most plants, they do not flower or seed, and instead produce spores.

They grow in dark, damp, shady places. Their roots are shallow, as moss seeks to attach itself to a rock or tree, to absorb the moisture that falls on them. Moss is beneficial to forests as moss will form a carpet that slows down and retains water, reducing soil erosion. Moss allows tree seeds a soft, safe landing, and a place for seeds to germinate.

Can Moss or Lichen be Hurtful to My Trees?


Mosses have different features, colors and textures, but despite their variety, they have one thing in common: they are almost never harmful to trees. In places like Oregon and Washington State, mosses can grow so thick that their weight can be harmful and cause breaking. However, in but New Jersey, it is not moist enough to have that degree of moss growth.

In rare cases, and with only certain species, when moss is girdling the tree, the moss can cause bark rot and be a breeding ground for some fungi and bacteria. Currently, billions of trees live harmoniously with moss as they are not parasitic and do not take nutrients from the tree.


While most funguses on trees can cause significant harm to the tree. Lichen is believed to benefit trees by providing nutrients. Because the lichen feeds off of algae, and algae uses photosynthesis to create food, Lichen tends to grow on trees that see a lot of sunshine. Often, these are trees that have lost their foliage to some other cause, which can lead some people to blame the lichen, however, the lichen could very well be preventing the damaged tree from suffering sunscald as well.

Preventing Moss on Trees

Despite the fact that moss is almost always harmless to trees, some people prefer not to encourage its growth. By pruning the tree and aerating the lawn around the tree, you can both discourage large puddles around the base of the tree and allow more sunlight in to dry the area. Some people advocate power washing moss off trees. This can cause significant damage to a tree and should not be done. (Tree professionals have special nozzles for spraying trees that do not cause harm.)

The Benefits to Both

Lichen and Moss are both important to our environment. The consume pollutants and CO2 from the air, making it cleaner to breathe. Moss creates a soft bed on the forest floor providing a healthy environment for new growth. An abundance of both is a good indicator of the overall health of an ecosystem.

The next time you are hiking in the woods or nature trail or walking along the neighborhood streets, take a look around and see if you can spot some of Earth’s natural wonders.

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