Understanding Lichens: Are They Harmful to Your Garden?

If you’ve noticed patchy, crusty, or moss-like growth on your trees or garden shrubs, you may be looking at lichens. These unique structures often raise some questions for gardeners: What are lichens; and should you be worried if they’re growing on your plants?

In this article, I will explore what lichens are, why they appear in your garden, and whether they’re a problem for your plants. Plus, I will share a few helpful tips on how to manage them if needed.

What Are Lichens?

Firstly, lichens are not a plant, a moss, or a fungus — they’re something much more interesting. A lichen is a combination of a fungus and either an alga or cyanobacteria living in a mutually beneficial relationship. The fungus provides structure and protection, while the alga or bacteria uses sunlight to photosynthesise and produce food.

This partnership allows lichens to grow in some of the most challenging environments; including on rocks, tree trunks, fences, and even soil. In gardens, they’re most commonly seen on tree bark, shrubs, and ornamental plants, especially in shaded or damp areas.

Are Lichens Harmful to Plants?

The short answer is no - lichens are not harmful to plants. They don’t take nutrients from the plant or damage the bark. Instead, they simply grow on the surface and use it as a place to live. Lichens don’t have roots and don’t draw moisture or food from the plant itself.

Close-up of lichen growing on tree bark, showing its textured, leafy and crusty surface in shades of green and grey.

In fact, lichens are often found growing on mature, slow-growing, or struggling plants — not because they cause poor plant health, but because the conditions that favour lichen growth (like still air, shade, and moisture) also tend to occur around less vigorous plants.

Lichens Are:

Non-parasitic
Not a disease
Harmless to bark or stems
Indicators of good air quality

Why Are Lichens Growing in Your Garden?

Lichens thrive in environments with:

Clean, unpolluted air
Consistent moisture or humidity
Low light or shade
Stable surfaces like tree trunks or old branches

Delicate, branching lichen growing on tree bark, with fine, bushy structures in pale green and gray hues.

If you see lichens in your garden, it’s actually a good sign that your local air quality is excellent! They're considered bioindicators, meaning their presence shows that your environment is low in pollution.

Should You Remove Lichens From Plants?

There’s usually no need to remove lichens unless you’re concerned about how they look. However, if you’d prefer to reduce their growth, here are a few gentle steps you can take:

Improve air circulation: Prune surrounding plants to let more light and airflow through.
Reduce excess shade: Trim nearby trees or tall shrubs that block sunlight.
Support plant health: Make sure your plants are well-watered and properly fertilised.

Avoid using chemical sprays or scrubbing lichens off bark, as this can damage your plants more than the lichens themselves.

Should Gardeners Be Concerned?

Lichens might look unusual, but they’re completely harmless to your garden plants. Instead of worrying about how to get rid of them, focus on creating healthy conditions for your plants — and enjoy the fact that your garden is clean and biodiverse enough to support these fascinating organisms.

Key Takeaways

Lichens are not harmful to trees, shrubs, or other garden plants.
They grow on surfaces but don’t steal nutrients or cause disease.
Their presence often reflects good air quality.
No chemical treatment is necessary — simple pruning and plant care are enough.

Bright yellow lichen growing on the rough surface of tree bark, showing a crusty texture and vibrant colour contrast.

Lichen FAQs

Where do lichens grow?

Lichens can grow in a wide range of environments, from tree bark and rocks to roofs and soil. They are incredibly resilient and can thrive in harsh conditions, including deserts, arctic tundra, and polluted urban areas.

Are lichens harmful to trees or buildings?

Lichens are not harmful to trees - they don’t take nutrients from the tree and are simply using the bark as a surface to grow on. On buildings, they may cause aesthetic concerns but typically do not damage the structures themselves.

How do lichens reproduce?

Lichens can reproduce in two main ways: through the release of fungal spores (which must find the right algal partner to form a new lichen) or by fragmenting and spreading bits of the lichen that already contain both partners.

Why are lichens important?

Lichens play crucial ecological roles: they help break down rocks into soil, provide food and habitat for wildlife, and are indicators of air quality, as they are sensitive to pollution.

What do lichens look like?

Lichens come in a variety of shapes, colours, and textures. They can appear leafy (foliose), crusty (crustose), or bushy (fruticose), and their colours range from greens and greys to bright oranges and yellows, depending on species and environment.

About the author: Steven McLean

I am an educator and passionate gardener and traveler. Throughout my adult life, gardening has been my passion, therapy, drive and source of purpose. Even as a child I had an intrinsic interest in plants and a desire to understand what makes them grow.

I distinctly remember the moment this began - my family was on one of our regular road trips from Hervey Bay; Australia. We were driving past a field of sugar cane. Dad pulled the car over and we cut a couple of sugar cane stems and brought them home for a treat. To be honest, I didn’t really like the taste, but I did want to try and grow it; and that is exactly what I did. It was then that my fascination, interest and passion for gardening and understanding plants began.

Fast forward a few years and I studied biological sciences and began what would be a 36 year career as a Biology educator. From this, I don’t only love gardening, but I also love helping others learn about gardening. I am also always looking for new ways to develop my own gardening knowledge. I like to think I am truly a life-long learner.

Fundamental to my beliefs about education is that learning is often best done as a part of a community - learning from others, and helping others to learn. It is this type of community that I hope iCultivate will be for its members - a community of gardeners, keen to share their gardening knowledge and wanting to learn about new ways to garden - a community built on the love of gardening.