A major problem for gardeners and arborists is the development of lichen on trees. You are no doubt familiar with lichen, even if you don’t know the actual term. Lichen is that strange, hard growth that grows along the bark of trees and nearby surfaces in a rainbow of blue, green, white, and gray.
Lichen doesn’t physically harm trees, but it can be a pain for anyone who wants to keep their trees beautiful and unmarred by this strange substance. After all, it tends to give trees an almost rotting effect. If it is growing on any of your trees – deciduous, coniferous, fruit, etc. – consider one of these methods to get rid of it for good.
How to Get Rid of Lichen on Trees
It can be frustrating to have watched a tree sprout from a small seed into a beautiful tree, only to be confronted with the reality of lichen. Lichen often forms patches all over the bark, covering the tree with green, brown, or even blue growths that are alien to everything a gardener knows. This often leads novices to go into damage control mode, followed by a frenzy of “burn it all to the ground” out of fear that the lichen will spread. Thankfully, this is not the case.
While lichen keeps itself close to tree bark, there are several ways to get rid of lichen on trees without harming the bark underneath. These methods work by targeting the structure of the lichen itself, which is one of the most unusual in the plant kingdom.
What Are Tree Lichens?
Lichen is a unique lifeform constructed by two others: fungus and algae. Sometimes a cyanobacterium can take the place of the algae if it’s not available. These organisms form a symbiotic relationship, meaning they benefit one another and use each other to survive. This symbiotic relationship creates a vegetative body called a thallus, which is the lichen you see on the trees.
The thallus’s structure is composed mostly of fungal fibers. The fungus cannot make its own nutrition, so it protects an interior deposit of algae or cyanobacteria, which produces food through photosynthesis. The result is the strange lichen you see growing on your trees.
Lichen lacks most of the elements gardeners associated with plants. There are no stems, leaves, water-storing waxy cuticles, or roots. Lichen doesn’t even feed on the tree bark, although many people think so. Instead, trees just serve as a convenient surface for the fungus and algae or cyanobacteria to grow undisturbed by the chaos on the ground.
So, when you want to remove lichen from your trees, it’s important to focus on using methods that work on fungi, algae, and similar structures. The methods below are some of the best for gardeners of all experience levels.
The Scrubbing Method
If you’re worried about damaging your tree by using sprays or chemicals on the lichen, consider avoiding them all together with the scrubbing method. The majority of lichens are harmless, and since they are made of fungi, algae, or cyanobacteria, a little soap and water are all you need. Lightly scrub the solution over the lichen, and it will fall off.
Be careful not to scrub too hard, though. If you do, you can accidentally take some of the bark off of the tree as well. If you’re not sure what kind of soap to use, the best solution is dish soap.
Lime Sulfur and Copper Sulfate
Lime sulfur is a material that should only be used by experienced gardeners. It is a white substance composed of calcium hydroxide and sulfur, a potent combination. It can only be used on dormant plants, as the powerful life will destroy any leaves, stems, or roots it touches. This is great news because it eliminates lichen, but bad news if you accidentally spread it to another part of the tree.
If you want to use lime sulfur, consider investing in a horticultural dormant spray that mixes it with oil. It can be applied directly to the lichen and will eat right through it. It can also be used to attack a variety of other problems, including black rot, black spot, blights, powdery mildew, and anthracnose.
Similar to lime sulfur is copper sulfate, which can be sprayed on lichen during late spring through early fall. Copper sulfate is another potentially toxic substance, so keep it away from leaves, stems, and roots. It also doesn’t work in cooler weather, so it must be sprayed in warm weather like the summer.
If you’re unsure about the best way to get rid of lichen, or simply don’t want to use soap or harsh elements near your trees, consider branch thinning. Lichen grows best in cool, moist areas that only receive sun part of the time. If the side of your tree has lichen on one side of it, consider thinning the branches above the area so more sunshine leaks through. It would also be a good idea to remove regular water sources, like a sprinkler, if they keep hitting that side of the tree.
Changing the environment of the tree and its lichen will take some extra time and effort, but it will help prevent the growth from coming back in the future.
If you are struggling with lichen in your garden, you’re not alone. These fungi/algae/cyanobacteria combinations grow in cold climates all around the globe and seem to enjoy trees because they provide an ideal location away from the dangers of ground. Plus, the branches of the trees offer protection from the warmth and sunlight that the fungi dislike.
If anyone of these methods does not work for you, consider trying them in descending order. So, wash with soap and water first. Follow up with lime sulfate or copper sulfate. If you’re still struggling, it might be time to prune and rearrange the yard.
Don’t let the lichen get the best of you. It’s a delicate symbiotic relationship, and it will be easy for you to disrupt it.
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