Lichen: What It Is and Should You Worry

An explanation of what this weird stuff really is

🌿 Garden Talk | by Guy Saldiveri | January 24, 2026 | Updated: February 21, 2026

We’ve all seen it, and we’ve all wondered—what is it, and where did it come from? More importantly, what is it doing on my tree or shrub?

Let's hit the most important part first—it's not an alien being, it's not a bad thing, and it certainly isn't hurting your plant. To be quite honest, it's actually a sign of a very healthy environment. It won't grow in areas with high pollutants, so its presence is a signal of good air quality.

Where it can signal a little concern is in the health of the plant. Not that it's attaching itself to a sick plant—this stuff will grow on cement blocks or wood if you let it—it just may indicate a bit of distress on the part of its host.

When a plant is stressed, its canopy thins and more sunlight reaches the branches, which makes the lichen more noticeable—not more harmful.

Let's break it down:

Lichen (pronounced LYE-ken) is actually a combination of fungi and algae living in a symbiotic state, and it doesn’t do any harm at all. It uses the host as a spot to grow just like the host itself uses the soil in the ground. It doesn’t have a parasitic or mutually beneficial relationship with the host; it just uses it as a platform to live. 

Fungi act similarly to roots, providing structure, and a foundation that sits on the branch. It also absorbs moisture and nutrients from the rain, humidity, and dust. The algae collect the sunlight and produce the sugars the organisms need to survive.

Lichen comes in all shapes and sizes. It can be a flat structure resembling moss, or it can grow outward with long, spiky branch-like tendrils. It’s one of nature’s stranger but very interesting designs.

Lichen is also a well used and vital source of nutrition for a wide range of insects and birds. Caterpillars, moths, and snails—as well as deer and squirrels—use the lichen as a healthy food source in winter months when other food is scarce. Birds use the lichen as nesting material and also forage inside for bugs and other insects. 

Seeing lichen is not a bad thing. On the contrary, it’s a vital part of the local ecosystem and should be welcomed. If you have an abundance of lichen, it is a sign that your local air quality is generally very good.

What to do:

Enjoy it, don't fret too much, and pay a little extra attention to the host if there’s a large presence. As previously stated, lichen’s presence is more noticeable when the host is under stress. A little more water… or a little less. Maybe some extra fertilizing. 

Just one of nature’s hints that something might need a little TLC.

Got some weird looking lichen? Leave me a comment, always love seeing new and interesting things.

Happy Gardening 🌱