We often get calls from customers about lichen on their trees, with questions about why lichen grows on trees, whether it’s harmful, if lichen means the tree is dying, how to remove lichen, and more. In this FAQ article, we answer the most common questions about lichen in Connecticut.
Have you ever marveled at those wrinkly, platy, fibrous, or brightly colored patches growing on your trees? Have you wondered what they are and if they’re hurting the tree?
You’re probably looking at lichen; one of nature’s most interesting creations. Read on to learn what it is and what it is (and isn’t) doing to your trees.
What is lichen?
Lichen is a living organism that is part fungus and part algae. These two components live in a mutualistic relationship, meaning that each benefits the other. The algae photosynthesize and the fungi provide anchoring filaments for the algae and collect and hold moisture.
Working together, these two components of lichen can survive in a range of environments, from coastal sea level to the arctic.
Is lichen a type of moss?
Although it is often confused with it, lichen isn’t a moss. Mosses are in a different family of primitive plants and have leaf, stem, and root-like parts. You’ll often find mosses and lichen growing near each other, which can lead to confusion.
One big difference is that lichen prefers full sun to grow, while mosses prefer more shade.
Where does lichen grow?
In short: lichen grows almost anywhere. If there’s sunlight and moisture, lichens will grow.
Unlike green plants with leaves, roots, and flowers that grow and are pollinated in ways that we’re familiar with, lichen is only a surface-living organism. It draws its growing requirements from the algae it grows with and from the atmosphere around it, not through roots.
This is why you’ll find lichen growing on rocks, roofs, gravestones, metal gates, glass, soil surfaces, and, of course, trees.
Does lichen grow in Connecticut?
There are tens of thousands of types of lichen found all over the world. Depending on their type, they may be yellow, orange, green, or gray, and may resemble foliage, hairs, or a powdery or crusty surface.
In Connecticut alone, there are hundreds of species of lichen that you’ll find all around the state. They’re found on forest trees, boulders left behind by glaciers, and on the state’s ubiquitous stone walls built by farmers after they harvested the rocks from their fields. The state’s oldest lichens (the ones that grew on the primeval forest trees that once covered Connecticut) are long gone, along with the trees themselves, but there are plenty more all around you.
How does lichen survive?
As long as the fungi and the algae that makeup lichen can draw moisture from the atmosphere and have enough sunlight to photosynthesize, lichen will survive. There’s no need to water or feed it; lichen can get everything it needs from its immediate environment.
Because of this epiphytic behavior, it can seem like lichen grow from nothing, in thin air. Of course, anyone who’s grown an epiphytic “air plant” knows that they need nutrients and water too, not just air - and it's the same for lichen.
Can lichen survive a drought?
Lichens aren’t able to store or conserve water so they will dry out during periods of drought. However, this doesn’t mean they’re dead!
When conditions improve, lichens will quickly absorb any available moisture, including rain, dew, and even water vapor, such as fog. They’ll even absorb moisture from the air itself if it’s very humid.
Once they’ve absorbed enough water, they’ll start photosynthesizing and growing again.
How does lichen spread?
Most lichens spread by growing across the surface of whatever they’re living on.
When they dry out, pieces of lichen often break off. These small crumbs can be blown to new locations by wind or carried by animals. If they land in a hospitable location, they’ll start growing whenever they receive enough moisture.
Will lichen hurt my trees?
No, lichen will not hurt your trees. Because of their structure and growth habit, lichen will grow on your tree but not into your tree. A tree’s bark is just a useful surface for lichen to attach to.
Because lichen has filaments that anchor it to a surface but no roots that take up water or nutrients, there are no connections from the lichen to your tree’s vascular system or energy stores.
Does lichen grow mostly on unhealthy trees?
Lichen will grow on both healthy, vigorous trees and on older or declining trees.
The health of a tree is not related to the appearance of lichen, although many people think lichens damage trees and associate lichen growth with a stressed or declining tree.
A tree’s bark is simply an ideal location for lichen because it provides everything lichen needs to grow:
- Sunlight
- Moisture
- A surface to attach to
So why do we see more lichen on declining trees?
An older, declining tree may have a sparser crown or leaf and branch dieback, which means an increase in sunlight that reaches branch and trunk bark where lichen grows. Rainfall and atmospheric moisture will also more easily reach the tree’s branches and trunk when they are not intercepted by leaves. These conditions will naturally increase the growth of lichen, as it’s a beneficial setup.
An older tree may also have more brittle and fissured bark which offers more places for lichen to attach to. Plus, an old tree may have stopped exfoliating its bark. Exfoliation is a natural process for many trees and a way that lichen is dislodged from a younger tree’s surface.
Another thing to remember is the slow rate at which lichen grows. It may take years of your tree’s life before lichen becomes extensive enough to be really noticeable.
No matter the age or health of your trees, the growth of lichen indicates that the air is clean (it won’t grow in polluted conditions) and moisture is available. So you shouldn’t automatically associate the appearance of lichen with negative factors affecting your trees.
Should I remove lichen from my trees?
Again, it’s a no. There’s no reason to remove lichen from your trees- except for cosmetic reasons. Lichen isn’t harming it and, more importantly for your trees, removing it may cause permanent damage to your tree.
If I want to remove lichen, how should I do it?
A tree’s bark is a sealed, waterproof layer of protection. Any activity that damages or removes bark can affect the tree’s health by allowing pests or diseases to get inside. So don’t use steel brushes, chisels, or any heavy tool to remove lichen.
If you absolutely must remove lichen, spray your branches with a gentle soapy solution. After wetting the lichen, you can use a natural-bristle scrub brush and gently exfoliate the lichen off. Don’t scrub hard, especially on young, thin bark. You can wash off the residue with a stream of water from your garden hose.
If your tree is in good health, you can prune off branches that have more lichen than is to your liking. But, in general, don’t prune if there’s not a solid reason for it, particularly during the active season of insect pests and diseases that can attack your tree.
Learn more about types of pruning for your trees
What else can I do about lichen in my tree?
If you think your tree has lichen because of its poor health, the best approach is to improve your tree’s health. This could include:
- adding compost around your tree,
- using a foliar fertilizing spray,
- ensuring your tree has enough irrigation, and
- treating any other diseases that might be present on your tree.
Since lichens need a lot of sunlight to thrive, a full-leafed and shady tree crown may be the best revenge.
See how trees in Connecticut benefit from supplemental fertilization
Are there any benefits to lichen?
While we can’t speak for its internal life, lichen does serve many external purposes.
In addition to it being an indicator of healthy air quality, lichen is a food source: animals, including squirrels and voles, will eat it; deer will gnaw at it in the winter, and some indigenous tribes in what is now New England would eat it as well when food was scarce. Birds include lichen as nest-building insulation.
NOTE: Some species are not edible and can be poisonous, so don’t just peel off a length of the first lichen you see and toss it in your mouth!
There is also a long history of humans using lichen. For centuries, lichens have been used for textile dyes. In the U.S. and Finland, lichen was used for its antimicrobial compounds to treat wounds and even athlete’s foot. These same extracts from lichen that have anti-bacterial properties are found today in toothpaste and deodorants. You may have lichen on you right now!
Want to learn more?
Below are two excellent sources of information about lichen in Connecticut.
- The University of Connecticut’s Home and Garden center
- Connecticut Botanical Society’s Facebook page has photos of lichen
Give Us a Call
We’re here to help if you have questions or aren’t sure if you’re looking at lichen or something else on your trees. If your trees are declining, it’s not because of lichen. However, we can evaluate and diagnose what is going on and give you a comprehensive treatment plan.
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