Old fruit trees and other deciduous trees in particular are often densely overgrown with lichens. Many a gardener suspects that these organisms damage their trees. But is it really like that?
Lichens usually do not harm fruit trees
What are lichens?
Lichens are not independent plants, but a community of fungi and algae. Both form a symbiosis in which they support each other. For example, fungi are able to take water and nutrients from the soil or air, while algae produce nutrients through photosynthesis. In this way, the two organisms condition and feed each other. There are around 2000 different species that can take on very different appearances, and the color spectrum also varies greatly. Lichens can lie loosely on their substrate, but some species are also strongly fused with it.
Do lichens damage fruit trees?
Because lichens tend to grow on weakened and old trees, many gardeners suspect them of causing significant damage. This is not true, since lichens are self-sufficient and do not depend on the fruit tree for food. They filter their nutrients from the air and not from the infested tree's pathways. These organisms also do not hinder the growth of the bark, 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: lichens prefer to colonize already weakened trees, as these no longer produce sufficient defenses. 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?
Fighting the lichen is therefore not necessary. However, what you can do is improve the conditions for your infested tree. This can be done by loosening the soil and fertilizing or by moving to a sunnier location. If the tree is heavily overgrown with lichen and often has to struggle with recurring pest infestations, removal can still make sense: some pathogens and pests like to hide in the organisms. However, the lichen can only be scraped off by scrubbing vigorously with a hard brush - chemical agents are not permitted for domestic use.
tips
Lichens are regarded as indicator plants for healthy, clean air: Since the organisms do not have any excretory organs, they are very sensitive to pollutants in the air. Ergo, you can be happy if you find lichen-covered trees in your garden: it simply means that the air is literally clean where you live.