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Filling Holes In Tree Trunks: How To Patch A Hole In A Tree Trunk Or A Hollow Tree

Filling Holes In Tree Trunks: How To Patch A Hole In A Tree Trunk Or A Hollow Tree


By: Heather Rhoades

When trees develop holes or hollow trunks, this can be a concern for many homeowners. Will a tree with a hollow trunk or holes die? Are hollow trees a danger and should they be removed? Should you consider patching a tree hole or hollow tree? Let’s look at these questions about tree holes and hollow trees.

Will Trees With Holes Die?

The short answer to this is probably not. When a tree develops a hole or if that hole gets larger and creates a hollow tree, most of the time, it is only the heartwood that is affected. The tree only needs the bark and the first few layers beneath the bark to live. These outer layers will often be protected by their own barriers from the rot that creates hollows and holes inside the trees. As long as your tree looks healthy, it is unlikely that the hole in the tree will harm it.

When you find holes and hollows, you need to make sure that you do not damage the outer layers of the tree in the areas of the holes. This can cause damage to the natural barrier and allow the rot to get into the essential outer layers of the trunk, which then can kill the tree.

Is a Tree With a Hollow Trunk a Danger?

Sometimes hollow trees are a danger and sometimes they are not. The heartwood of the tree is technically dead, but it does provide important structural support to the trunk and canopy above. If the area where the tree has been hollowed out is still structurally sound, the tree is not a danger. Remember, a strong storm can put extra pressure on a tree and a tree that seems structurally sound in normal conditions may not be able to withstand the extra stress of high winds. If you are uncertain if the hollow tree is stable enough, have a professional arborist examine the tree.

Also, be aware that studies have shown that filling in a hollow tree often does not improve the stability of the tree. Do not rely on simply filling in a hollow tree as a suitable way to make a tree more stable.

Remember to recheck a hollow tree regularly to make sure that it is still structurally sound.

Is Filling Holes in Tree Trunks a Good Idea?

In the past, it was often recommended that filling holes in tree trunks was a good way to correct the tree hole. Most tree experts now agree that this advice was incorrect. Filling holes in trees causes problems for several reasons. The material that you fill the tree hole with will not react to the weather in the same way the tree wood will. The material you use will expand and contract at a different rate, which will either cause more damage to the tree or can create gaps where water (which leads to more rot) and disease can get trapped.

Not only that, but if the tree must be removed at a later date, fill materials can create dangerous situations to the person removing the tree. Imagine if someone using a chainsaw were to hit a concrete fill that they were not aware of in the tree. If you have decided that filling a hole in a tree trunk is your best option, make sure that you use a softer material, such as expanding foam, to do so.

How to Patch a Hole in a Tree Trunk

The recommended method for patching a tree hole is to use a thin metal flap or screening covered with plaster over the tree hole. This will prevent animals and water from entering the hole and create a surface that the bark and outer living layers can eventually grow back over.

Before patching a tree hole, it is a good idea to remove any water from the hole and any soft rotted wood. Do not remove any wood that is not soft as this can damage the outer layer of the tree and allow disease and rot to enter the living part of the tree.

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Real question: My mom has an old oak which has developed a cavity between two roots which is hollow out into the tree and is holding water. Can I fill this in with soil and cause no problems? Should I fill with something else- foam? Should I leave alone?

Answer: We get a lot of variations of the above question and typically the best way to handle this is to do nothing unless you can find an elegant way to divert the water. Why? We commercially available cavity fillers haven’t shown to improve the tree health and outcomes. In this case putting soil in the cavity might just make it a breeding ground for pests that can invade the hole. The other idea that comes up is drilling a hole to let the water leak out but again this has a way of creating a hole that pests can enter or promoting further decay in surrounding wood.

I guess it could be argued that standing water could also attract fungii or pests as well. Generally we say to leave it alone. There is no consensus among arborists that standing water will increase the hollowing of the tree.

Here is a great explanation published by the University of Florida Extension Agent

“Cavities and hollows in trunks and branches are typically the result of decay that followed injury. The injury often occurred many years ago (see photo). Injuries could include removing a branch with a pruning cut made too close to the trunk, removing a large branch, large branch breakage, topping the trunk or branches, cutting a large root or a group of roots (see right photo), or damaging the trunk.

In the old days, cavities were filled with concrete in hopes that this would strengthen the trunk. We now know that this actually causes more injury to the tree. Additional injury occurs when the tree continues to move normally in the wind against the stiff concrete column inside. This abrasion allows decay to move into the living wood by injuring the barrier zone formed by the tree to retard further advance of decay. Never use concrete in trees.

Cavities do not have to be filled. Spray insulation has been used to keep animals and children out of cavities. This should not injure the tree as long as the walls of the cavity are not injured during the repair process. Do not attempt to clean out the inside of the cavity or hollow. Do not drill holes in the bottom of the cavity to remove water. This is likely to spread decay to healthy living portions of the tree.

If a tree has a cavity or hollow and is near a building or area used by people, have it checked by a competent arborist. Hollow trees are not always at risk of falling down but they can be if the tree lacks enough healthy wood to keep it standing. Ample woundwood growth on either side of the hollow (as shown above right) can compensate somewhat for the weakness represented by the decay. This wood often is stronger than normal trunk wood.

Many arborists have come to understand that a tree trunk can loose up to about 70% of its wood cross-sectional area in the center and still retain about two-thirds of its strength provided there are no openings in the trunk. When there is an opening in the trunk (a cavity as shown above) the tree is typically regarded as even weaker. Specially designed tools operated by trained personnel can help determine the amount of decay in trees.”


Is there any treatment for tree trunk rot? Can I repair it?

Let’s start by answering Andy’s question: We don’t recommend cutting off and sealing a rotting portion of a tree trunk.

Cutting rotten wood leaves the plant vulnerable to more infections, which makes the situation worse. That's because trees can’t “heal” damaged tissues. They try to “seal” them off and continue to grow.

Plus, wound dressing (also known as tree paint) doesn’t close wounds or prevent the spread of diseases. It may hurt more than help, which could waste your time and money.

Trying to cut out the problem wouldn’t solve anything because the issue is deeper than that.

Trees rot because of a disease called wood decay, which usually targets old, large specimens and infects their wood from the inside out.

In most cases, it’s tough, if not impossible, to treat wood decay.

Here’s what you want to do instead if your tree trunk is rotting: call an ISA Certified Arborist® asap.

Rot could be a sign that your tree's weak or unstable . You want to know right away if it's at risk of falling on your home (especially if you’re in the middle of a nasty storm season).

During the inspection, your arborist can talk to you about options. She could recommend one of the steps below:

  • Leave it to your tree. If it’s healthy and the decayed area is small, there’s a chance that it will seal over the rotting wound as it naturally grows new wood.
  • Initiate PHC (plant health care).Water. Fertilization. Pruning. They can all do wonders to help extend the useful life of your plant (if it isn’t at risk of falling!). Also, take care and try to avoid any additional injury to the tree.
  • Remove it for safety if trunk rot has weakened the tree to the point where it poses an unacceptable risk to people or property.

Ready to talk to your local arborist? Click here.

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Patching Tree Hole: Fixing A Tree With A Hollow Trunk Or Hole In Trunk - garden

I'm currently thinking about your problem. Is it possible for you to take and post a pic? See go advanced/manage attachments.

One question is just how much of a structural repair is this?
I'm thinking drilled holes with rebar welded in place. Fire extinguisher handy. Like drill top, drill bottom. Weld rebar side to side.

I'm also thinking using rock and reinforcement screening like used for concrete.

Rockite has no "t". I'll have to review the datasheet.

Without having experience and I might even suggest practicing on a vertical 2x 8 with a large hole like 4" and a plate nailed to the back.

One of the hard parts will be creating a form. It has to be depressed from the surface, probably around 1/4" or about the active growing area.

What I'm thinking you can do is get some 1/4" stiff screen and make a few furring strips. Also get some teflon sheet (really thin). I have a source for I think 12" wide stuff.

You can build these in sections ready to bolt in place. I'd take some carpet thread and sew the teflon into the form. Say you made 3 of these.

Tack the bottom one with the furring strip. Mix enough to fill this section. Add the next section (already formed) with the furring strips. Finally add the last section. Might have a 2" hole or so in it. Then wrap something to hold the teflon in place.

The form should remove without sticking.

This stuff flows, so it won't stay in place being that thick.

And as you have read, you have to kill the ants, clean the rotten wood from the inside and keep it dry.

Your repair also has to not allow water to collect and be such that the tree will try to repair itself naturally.

I took some pics of my repairs and you may motivate me to make a sticky.


Tree, heal thyself / Tendency to plug holes in trunks is understandable but misguided

This coast live oak lived for over eighty years with extensive decay. It is best to let the tree deal with the decay itself. Handout

Q: I have two very old oak trees that each have a hole in the trunk about 2 feet in diameter that was there when we built our house 30 years ago. Tree specialists have said to leave them alone, which seems to be a bad idea as water is sitting inside the trunk and may cause rot. I staple plastic material over the cavities to keep out the rain and remove it after the rainy season. Should I also fill the cavities with sand or concrete?

A: Your intuition may tell you that if you have a decay cavity you should clean it out and fill it with Crest, Colgate or concrete. Like the cavities in our teeth, tree cavities never fill in on their own, but that is where the analogy ends.

Trees do not heal like humans. They compartmentalize or wall off decay by filling the cells around the cavity with antibiotics and fungicides that the trees make themselves. They also plug the vascular system around the wound to prevent the spread of decay.

The new growth will contain a zone of special cells to resist the spread of decay. Water sitting in the cavities may actually slow decay because water favors bacteria over fungi, and bacterial decay generally progresses more slowly than fungal rot.

So I am happy to report that your arborists are right and righteous, even if it is bad business. However, tree cavities filled with water make wonderful habitat for mosquitoes, and mosquitoes are wonderful habitat for West Nile virus. So you may want to empty your tree cavities before the mosquito season.

Q: I was shown the largest giant sequoia growing on the grounds of the Ahwahnee Hotel in Yosemite. I was told that the tree was planted about 80 years ago in honor of the birth of the granddaughter of the hotel developer. The tree was at least 6 feet in diameter, probably wider than the redwood cross section hanging in Muir Woods said to be 2,000 years old. The Yosemite tree is situated beside a tiny stream, probably providing maximum growth.

I have always believed that coast redwoods are faster growers. Would you please explain the difference shown here?

A: Size does not indicate age. In fact, you and I will shrink with age, although we may grow in belt and nose size. A lot of factors affect the rate of growth and the ultimate size of trees, particularly when it comes to redwoods. Coast redwood is extremely efficient at photosynthesis. Therefore, it can live as a suppressed dwarf in dense shade for many decades. On the other hand, its photosynthetic prowess can make it grow like Godzilla when it has a lot of sun and growing space.

Consequently, a 200-year-old redwood may be less than 6 inches in diameter or more than 60 inches in diameter. Environment (soil quality, access to water, sun, growing space and temperature) is the dominant influence on rate of growth and ultimate size.


Dealing with Tree Cavities

By Jeff Rugg

Q: We have a can of spray foam that says it can be used to fill cavities in tree trunks. There's a hole in one of our trees where a branch was removed — it's about waist-high. The hole extends up and down inside the trunk. It seems to be about half the diameter of the trunk, which is about 2-feet thick. Will spray foam protect our tree? I have also heard that concrete or mortar can be used.

A: Using polyurethane foam isn't necessarily the best way to care for most trees. Only a paper-thin layer of tissue under the bark of a tree trunk is live wood the outer bark and the inner wood are dead. As we know, dead things decay. Decay organisms — mostly fungi and insects — are found in tree trunks.

It may seem like filling the hole could prevent fungi and insects from decaying more dead wood. Unfortunately, what will really happen is the foam will trap moisture in the cavity and allow these organisms to work unseen. It won't seal all of the nooks and crannies in the cavity, and as the tree flexes in the wind, gaps will develop between the foam and the wood. Fungi and insects will survive in these gaps and perpetuate the decay process, making the gaps even bigger.

Trees naturally try to seal off a wounded area in their trunk by releasing chemicals that prevent decay organisms from surviving. Sometimes this works sometimes it doesn't. Animals may enlarge the hole, which can allow decay organisms to get past the tree's defenses.

Using something solid like concrete to fill a hole not only hides the decay organisms, but it also creates an inflexible area in the trunk that can cause the trunk to break at that point. Concrete will eventually crack and allow water and decay organisms into the cavity. It's also impossible to pour wet concrete above the entrance to the cavity. Drilling a hole above the cavity to pour concrete in would damage and weaken the trunk even more. Eventually, the tree will need to be cut down, and it will be harder to cut up the pieces with concrete in the trunk.

Instead, leave the cavity open so you can monitor decay organisms and the rate of decay. If you see harmful insects, such as carpenter ants, apply an insecticide. Pull out any loose rotting material by hand — don't scrape it out with tools because they could damage the natural chemical barrier the tree has built inside the cavity. You can also spray a fungicide in the hole if you like.

It is a good idea to consult a licensed arborist to determine the best long-term care for the tree. Hollow trees can become a hazard, so don't put off getting appropriate care for the tree.

Q: For the past few days, a pair of robins has been attacking our living-room window. We closed the curtains, but that didn't work. We hung strips of cloth on the window — that worked a little. We put some stickers of a hawk on the window, and that stopped them a little more. How can we get them to stop?

A: There are a lot of bird species that have been seen defending their territory from an imaginary foe: their own reflection. Usually it is the male, but sometimes it is the female, too. They see the intruder in unusual places, like windows, car mirrors and chrome materials on vehicles. The easiest thing to do is to change the reflection. No, don't paint a mustache over the bird's reflection. Put a piece of paper or cloth over the outside of the window so they can't see their reflection. The defense phase only lasts a few weeks, so you won't lose your window view for too long.


Watch the video: Filling an old tree hole.