I’m sure all of us have walked by a tree and noticed it has a hole in it. It might have been a tiny hole, like one a bug or bird made, or it could have been a cavity in a tree that is big enough for an animal to live in. But what do you do when you find a hole in your tree?
Trees can get holes in them for a variety of reasons, but you may want to fill these cavities to keep animals out, or to keep up with aesthetic purposes. To fill these holes you can use spray foam, mesh wiring, or wound coverings.
Trees are actually pretty resilient and a lot of times, they might not even need to have the cavity that is in them filled. If you are concerned about a cavity in a tree, read on to learn some helpful tips to help you in your tree cavity endeavors!
Why Do Trees Get Holes in Them?
Trees can get holes in them for a few reasons, but usually, no reason is a great reason to have a hole in your tree. Like I said before, the holes in the trees you notice might be small or large depending on how they got there.
Let’s start small!
What Causes Small Holes In Trees?
Beetles
According to the University of Connecticut, if you see a small hole in a tree there is a good chance it came from some sort of boring insect (like a beetle) or a bird that picks through the bark and makes holes.
First, let’s discuss bugs making holes in trees. Typically, a bug that makes a hole in a tree is a beetle and it makes a D-shaped or oval-shaped hole in the tree when it burrows in through the bark that is about the same size as a beetle.
Beetles like trees that aren’t necessarily healthy because it’s easier for them to burrow into if it’s a little bit decayed. Beetles like to get under the bark to lay eggs so that they stay nice and safe.
Once they find a good tree, they will signal for other beetles to come to that tree too, so usually, it is a problem if you notice beetles in your trees.
Birds
Woodpeckers are probably the most notorious bird for making holes in trees. They peck holes into trees so that they can feed off of the bugs inside the bark and they have a very distinct tapping sound when they do this. Woodpeckers make bigger holes in trees and they are usually pretty misshapen (not a perfect circle) and have rough edges.
Sapsuckers are another kind of bird that might make holes in trees, but unlike the woodpecker, the holes they make in trees are small and uniform and they usually look like they are in a grid pattern and put there with a purpose.
When it comes to bird and beetle holes in your trees, you don’t want to patch them up or fill them because it would damage the health of the tree and if there are beetles in them, you will just be trapping them inside to harvest the inside of the tree.
For these situations, you will need to use pest prevention and extermination methods to keep your tree healthy. However, if you have a larger, cavity-like hole in your tree keep reading and we can learn how to fix those.
What Causes Large Holes In Trees?
Tree Gets Injured In Someway
Tree cavities can happen in a few different ways, but typically they happen due to an injury according to Kansas State University. Usually, a tree gets injured and then in place of that injury comes a cavity, and then the cavity is typically followed by decay due to the excess water that sits within the cavity.
When a tree gets a cavity in it and then it starts to decay, it can start to eat away at the cavity and inevitably make a tree hollow. This sounds very intimidating but it’s a fact that a tree trunk can lose up to about 70% of its wood (if you were to cut a cross-section and look, about 70% would be missing) but the tree keeps most of its strength, ⅔ of it.
Mississippi State University explains that the reason the injury turns into a cavity is that bark is to a tree what our skin is to us. The tree is essentially getting a scar.
The bark is the first line of defense for a tree and so a broken barrier (again, a lot like us with our skin) can lead to things like unwanted pests that can damage a tree if it’s not strong enough to withstand the injury.
It may come as no surprise, but there are more wounded trees with cavities in industrial and residential settings because they have more contact with humans! Because of this, they have more contact with lawn mowers, weed whips, cars, etc.
Some common injuries trees might gain a cavity from are things like pruning too close to the trunk when the tree is young, damage to the trunk of the tree when young, cutting of a large root, big branches being removed or damaged or tree trunks, and branches that have been topped.
Why You Should Fill A Hole In Your Tree
To Preserve A Healthy Tree
You might want to fill the cavity or hole in your tree to try to maintain a healthy tree. When a tree gets a cavity, usually the cavity pools with water from the elements as trees do not absorb water through their bark or their wood inside the bark, only through the roots.
Because of this, that can cause a tree to start decaying and when decay happens it can not be reversed. The most you can do for a tree is limit the amount of decay the tree is exposed to.
To Keep Animals
If you have a tree cavity, you might be wanting to fill it because your pets are interested in going into the cavity and you are worried about the integrity of the tree or perhaps you don’t want any animals or insects living in the tree.
If the tree near your house has a cavity, it’s safe to bet that you don’t want something like a raccoon living in that tree cavity because they cause more problems than just having a hole in your tree.
Overall, this isn’t a bad reason to want to fill a cavity in your tree. This is to help keep keep pests away from your home.
To Keep Up With Aesthetics
Some people just don’t like a tree in their yard to have a hole in it so they want to fill it in and make it look whole and healthy. As stated before, trees can still be pretty healthy with a cavity in them but it might look nicer if you were to fill the cavity.
If you want to fill a cavity in your tree for aesthetic purposes, I strongly suggest also ensuring you are looking for the tree’s best interest to help preserve its health and wellness too so that you don’t end up having to cut it down due to damage because of aesthetics.
To Fill Or Not To Fill A Tree Cavity?
Filling tree cavities versus not filling them has been a debate recently among all tree enthusiasts alike. The go-to solution for a long time was to fill a tree cavity with concrete, but it is now becoming more and more evident that the solution they used to use doesn’t work in the long run.
Reasons To Fill A Tree Cavity
Some people say a cavity in a tree is like a cavity in our teeth, and wouldn’t we want a cavity in our teeth to be filled? This is a valid argument, especially considering that, like mentioned before, a hole in a tree shows that the tree went through some sort of trauma, so shouldn’t we bandage it like we would bandage our wounds?
The Center for Disease Control (CDC) states that a lot of times since these cavities fill with water, mosquitoes will try and make holes in the cavities and lay eggs there and hatch more and more mosquitoes.
So, if you were to fill the hole, you would be causing there to be fewer mosquitoes which would be a healthier environment for a lot of different parties involved like animals and humans and it would rid the area of those pesky little insects.
It’s also said that if you leave a cavity untreated, it might just be left open for more damage from the elements (water pooling causing decay), and more animals and bugs might crawl into the opening and cause greater harm than good to the tree.
Reasons Not To Fill A Tree Cavity
Tree cavities can be great spots for animals that would otherwise not cause any damage to the tree. Cavities can be home to many animals like squirrels, mice, owls, doves, snakes, etc. all of which don’t cause any damage to the tree other than just taking up space.
In fact, they might be doing the tree a favor living in it! After all, the animals usually form some sort of barrier (sort of like a door) to keep the elements out for the most part which might actually in turn help reduce decay in a tree because it would give the tree a chance to dry out. They make friendly housemates after all!
To learn more about the kinds of creatures that live in trees, check out our article 9 Different Animals And Insects That Live In Trees.
Trees can form a callus on them to cover wounds and if this happens, it is a great way for them to hold out excess moisture. So if an animal were to make their home in a tree cavity and keep it dry and the tree was able to create a callus, it would be in favor for both parties involved.
Mississippi State University says that you should not cover or fill small holes or even small cavities in the tree because the tree will more than likely heal itself. It would be the equivalent of us getting a small cut. If we let it breathe, it will heal.
Still Unsure Whether Or Not To Fill The Tree Cavity?
If you are still unsure if you should fill in a tree’s cavity or not, the University of Florida suggests that you call an arborist to come out and look at your tree for you.
A lot of people are worried about trees with cavities being a fall risk, and if you are worried you should call your local tree professional to come and test how sturdy your tree is and if it can withstand things like storms and wid.
Arborists can assess the damage and tell you what percent of the tree’s strength is damaged so that together you can make a mutual decision about what you should do from there.
How to Fill A Hole In A Tree
If you’ve moved on and made the choice to fill the hole in your tree, you have a few options. Let’s take a look at a few!
Spray Foam
The most popular option is to use a can of spray foam to fill in the tree cavity. According to Kansas State University, this is the best method for filling in a cavity.
Using spray foam doesn’t heal a tree and if decay has started within the tree it won’t stop it. However, it will make a great filling to keep kids, animals, and insects out of the cavity in the tree.
There are two different types of spray foam you can pick from, closed and open cell foam. Closed-cell foam doesn’t absorb water, so it won’t absorb any water that falls (like rain) but it also won’t absorb any water that is in the tree cavity.
The open cell does absorb water, but if you only have an open cell and you want to use it, you can paint it when it dries so that it doesn’t absorb water.
When using spray foam, it is suggested to use a template so it packs the foam in better. You can make one easily by measuring the opening cavity and then cutting a piece of cardboard (or anything you can find) to that size, holding it on the opening which you spray foam into a hole cut into the center of the cardboard.
When you can no longer spray foam into the hole and it starts to come out of the hole, you are done. Leave the template there until the foam dries (this also helps to keep animals and bugs out of the foam) and then peel it off when the foam is dried.
The CDC recommends cutting off any excess foam that you get if you overfill the tree and disposing of it properly to avoid an animal munching on it.
Great Stuff Big Gap Sealant is a great spray foam to use to fill cavities in trees and this particular sale comes with 3 cans to ensure you have enough to finish the job well.
Wire Mesh
This can be used by itself or in conjunction with the spray foam. If you use it with the spray foam, simply cut the wire mesh to size and place it over the foam when it is drying so that it sticks.
If you use it with the spray foam, it’s a good way to keep smaller animals (like mice and squirrels) from digging into the spray foam to make a home in the cavity regardless of your efforts to keep them out, so make sure you use mesh that has narrow openings (according to Kansas State University).
If you use this mesh by itself, make sure you are not putting a lot of stress on the tree by using a lot of nails or screws to keep it in place. If you can, just try and fit it snugly in the opening of the cavity with very few modifications.
304 Stainless Steel Woven Wire Mesh Screening is a great option because it has narrow openings to keep out even the tiniest pests and it also comes in sheets so it is easy to manipulate and cut to size.
Preventative Wound Coverings
Mississippi State University suggests that you take preventative measures to help your trees when they are wounded so that if they do form cavities, they are small and manageable.
If you notice your tree looks wounded or you witness a tree get wounded, you can get petroleum-based tree paint to fill in the wounds. When you do this, it helps the wounds to create a callus faster and to overall heal itself quicker.
Treekote Tree Wound Dressing is perfect for this and it comes with a lid that has a brush attached for easy application and fewer tools for you to gather when trying to help your tree.
Helpful Tips for Filling A Tree Cavity
When filling a tree cavity, Kansas State University suggests that you should try and keep any added damage you make to an absolute minimum. You do not want to clean out the cavity before filling it with anything or before covering it up.
You also don’t want to remove any of the ]punky wood you see although it might be tempting. You might see it due to moisture, but that punky wood is the tree’s barrier between decay and healthy wood so by removing it, it’s like picking a scab, you’re just exposing the tree to new harms.
The CDC recommends that you do not use concrete, gravel, or sand to fill in a tree. Concrete used to be the main method for filing trees, but it became pretty dangerous as it was heavy and if the tree didn’t have structural support, concrete didn’t fix that. It would cause more trees to fall and now they were heavier and it’s not flexible at all.
Sand and gravel are also not the best options because they can pose a big safety risk if the tree were to ever need to be removed, especially if the arborist or even average joe cutting the tree down didn’t know it was filled with sand or gravel. It also can add a lot of unnecessary weight to the tree-like concrete can.
In Conclusion
Overall, tree health is the most important factor we should be looking at, and getting an arborist out to assess the health of the tree will be vital in this step of the process. Once you can agree with the arborist on how healthy or unhealthy your tree is you can move on to deciding where to go from there.
Spray foam, mesh wire, and preventative wound measures are your best bets in keeping a tree and its cavity healthy if you prefer to treat rather than see if nature heals itself. Just make sure you aren’t adding any new damage to the tree!
Best of luck taking care of your trees!
References
Boyle, W. A., Ganong, C. N., Clark, D. B., & Hast, M. A. (2008). Density, distribution, and attributes of tree cavities in an old‐growth tropical rain forest. Biotropica, 40(2), 241-245.
Gysel, L. W. (1961). An ecological study of tree cavities and ground burrows in forest stands. The Journal of Wildlife Management, 25(1), 12-20.
Levison, J. J. (1909). Filling Tree Cavities. Mycologia, 1(2), 77-79.
Lindenmayer, D. B., Blanchard, W., McBurney, L., Blair, D., Banks, S., Likens, G. E., … & Gibbons, P. (2012). Interacting factors driving a major loss of large trees with cavities in a forest ecosystem.
Maziarz, M., & Wesołowski, T. (2014). Does darkness limit the use of tree cavities for nesting by birds?. Journal of Ornithology, 155(3), 793-799.
