What are lichens?
Lichen is not a plant in its own right, but a community of fungi and algae. Both form a symbiosis in which they support each other. Fungi are able to take water and nutrients from the soil or the air, while algae produce nutrients with the help of photosynthesis. In this way, the two organisms condition and nourish each other. There are around 2000 different species that can have very different looks, and the color spectrum also varies greatly. Lichen can lie loosely on their subsoil, but some species are also strongly fused with it.
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Does lichen harm the fruit tree?
Since lichens predominantly overgrown weak and old trees, many gardeners suspect them of causing considerable damage. This is not true because lichens are self-sufficient and do not depend on the fruit tree as a food source. They filter their nutrients from the air and not from the pathways of the infected tree. These organisms do not hinder the growth of the bark either, after all, due to the lack of roots, they do not penetrate into the Cambrian - where the bark is formed. However, their presence is often a sign that the tree is not doing well: Lichen prefers to colonize already weakened trees, as these no longer produce sufficient antibodies. This is especially true for trees that suffer from a lack of nutrients or that are too dark.
When and how should lichen be removed?
It is not necessary to fight the lichens. What you can do, however, is improve the conditions for your infested tree. This can be done by loosening the soil and fertilizing or by moving it to a sunnier location. If the tree is heavily overgrown with lichen and often has to struggle with recurring pest infestation, removal can still make sense: some pathogens and pests like to hide in the organisms. However, the lichens can only be scraped off with vigorous scrubbing with a stiff brush - chemical agents are not approved for household use.
Tips
Lichen are considered indicator plants for healthy, clean air: Since the organisms have no excretory organs, they are very sensitive to pollutants in the air. Ergo, you can be happy if you find trees overgrown with lichen in your garden: This simply means that your air is literally clean.
