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I am trying to determine the best way to attach trail signs to trees in the woods.

The problem with trees is that they grow. If you firmly embed a nail in the wood, the tree will eventually grow around the nail head. When we put up small plastic trail markers (what we use a blazes), we deliberately leave a ½ inch or so gap between the nail head and the marker. Put another way, we don't bang the nail in all the way. This gives the marker room to slide along the nail, instead of the growing tree pushing all around behind the nail head, and eventually buckling and cracking the plastic marker.

I am now going to put up some aluminum signs that will last much longer than the plastic trail markers. A tree could grow multiple inches over the expected life of the sign. What I'd like is a way to mount the sign so that it stays on the outside, moving with the growth of the tree instead of getting swallowed up by it.

It seems that just the right diameter and length of nail might do it. You want the sign to be held, but the nail be able so slide out as the tree grows and pushes against the sign. What diameter and depth might that be? What studies are there that have looked into this? What experience do you have with this?

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    When I read the title, I thought "does he know what the trees are thinking? How does he know which trees are considering growth?" – Mr Lister Mar 17 '15 at 9:52
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    If you are nailing the signs or stakes to the tree as suggested above, never use steel nails, always use aluminum. In the future, a sawmill operator will thank you. – user5731 Mar 17 '15 at 16:12
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    For some species and in some ecosystems, penetrating the bark with anything or letting the tree engulf anything would put the tree at risk for infection or otherwise damage it to an extent generally considered unacceptable. For example, this is true for most trees in the arid American west. You don't say where your projects take place, but it sounds like this may not apply to your situation. However, I wanted to raise it as a caution for generalization of answers. – Reid Mar 19 '15 at 20:11
  • From an anonymous user: expandfarmproducts.com – ShemSeger Jan 7 '16 at 20:05
  • @Reid I was going to flag you as "tree hugger", but nevermind... – Kyle Mar 18 '16 at 12:28
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Given that trees don't push outward, one option is to use lag bolts, and once a year two go around and turn them out a little bit so they are never engulfed in the growth.

The amount of turning you'll need to do and the frequency will depend on the speed of growth and how secure you need the sign. If you can leave a half-inch out of the tree and have the sign hang on it, as you are currently doing with nails, and if they are slow growing trees, you may only need to turn them every few years. Fast trees with no bolt head gap may need to be loosened twice a year or more.

While the signs are light a thicker lag bolt than necessary should be considered so you can exert the force required to loosen it after the tree re-seals the damage caused by it and makes it much harder to turn initially.

There are a lot of resources about fixing items to trees in the tree house communities and businesses on the internet. There you can find out more about how trees grow with items attached. There are situations where a tree will exert apparent pressure on items affixed to the outside, but the issue is that the pressure isn't great enough to overcome the friction of the fastener into the heartwood. Most accounts suggest that if small nails are used on large flat boards, some trees will push the board away, pulling the fasteners through. Otherwise the board is engulfed as well, becoming part of the tree (and a vector for disease and damage)

Treehouses are usually built using lag bolts with several inches of space between the tree and the board attached to the lag bolt. Once the tree grows to the board, the tree house must be adjusted to move the board away from the tree again, and the lag bolt loosened or re-positioned depending on the tree house redesign.

Stainless steel or hot dipped galvanized bolts are needed for long term tree attachment use.

  • Thanks. This is exactly the kind of answer I was looking for, although not the answer I wanted to hear. Can you provide a few links to the "lot of resources" you mention about fixing items to trees. – Olin Lathrop Mar 17 '15 at 14:00
  • @OlinLathrop I've added the three links I found most relevant to your situation. They focus on treehouses, so there's a lot of information not relevant, but there are sections in each that are relevant. – Adam Davis Mar 17 '15 at 14:42
  • This would work, but it requires regular maintenance. You would have to make sure the sap seeping from the wounds inflicted by the lagbolts doesn't glue the sign to the tree. You may have to knock it loose from the trunck every time you adjusted the blots. – ShemSeger Mar 18 '15 at 16:00
  • @ShemSeger Yes. There's no automatic way to do what Olin wants to do, though. Every method will require maintenance. Some trees will weep sap, but most won't after a short period of time when the tree seals tightly to the lag bolt. – Adam Davis Mar 18 '15 at 16:03
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What you're asking to do is impossible to accomplish.

The signs will never, "move outward with the tree as it grows". Trees don't grow like that. The reason trees have rings is because they grow layer-by-layer each season. If you tie a thread around a tree, the tree will not grow and break the thread, it will grow around it. Similarly, you're not going to get a sign to move outward as a tree grows because the layers (rings) that you've pounded your nail into never move. The tree will engulf your sign as new layers grow each year.

It's for this reason that you'll notice that most signs in parks are nailed to posts that were planted into the ground, or are nailed to dead trees that do not grow.

If live trees are the only option you have for sign posts, then I would recommend doing what the logging companies do for their signs:

Nail a stake to the tree, and attach your signs to the stake:

enter image description here

This way when the tree grows, it'll only engulf your stake. These signs are far more visible in the woods too, they hang out over the trail, and they're visible from both sides of the tree.

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    I would also add that for the sake of the trees, please find another way. Holes in trees are routes for invaders of all sorts. Your sign will go away eventually, likely before the tree dies. Use a stake or something other than a live tree. – Scott Baker Mar 17 '15 at 17:47
  • I already kind of imply that when I say, "If live trees are the only option you have for sign posts..." And I do mention that posts and dead trees are preferred for signs in parks. – ShemSeger Mar 17 '15 at 17:55
  • @Scott: Live trees are really the only realistic options at trail intersections. Posts cost money, need to be carried to the site, are difficult to dig holes for, and don't keep the sign high enough to be out of reach of casual vandals. – Olin Lathrop Mar 18 '15 at 15:56
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    I can't help but think about this question like a programming problem. Programmers always choose the zero maintenance solution. – ShemSeger Mar 18 '15 at 16:05
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Coming from a heavy ranching area the method used for properly attaching fences to trees is to add a board in between. The board provides enough surface area and strength that instead of the tree growing around the nail it pushes it out .

  • Good point. I can put a backing board behind the aluminum signs. What kind of nails do you use for this case (length into tree, diameter, material)? And in case it matters, what kind of trees? – Olin Lathrop Mar 16 '15 at 21:15
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    I know what you're talking about. This doesn't work the way you think it does. The tree still grows around the board, it just takes a lot longer. I'm from a ranching area too, I've seen old fences where the board was almost all the way in the tree. – ShemSeger Mar 17 '15 at 0:59
  • Part of that depends on the fastening system used. I've seen both happen on the same fence. Clearly if you're using ringshank nails, hot dip galvanized nails or screws it's not going to work anywhere near as well. – dkippers Mar 17 '15 at 22:13
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You are probably finished with this project by now, but I'll weigh in with our experience for others searching for this answer down the road.

We were wondering the same thing about how to attach horticultural signs to trees a couple of years ago. We manufacture interactive plant tags for trees and other plants and many of our users attach our larger signs to mature trees instead of mounting on plant stakes.

We interviewed a lot of people and ended up visiting Bartlett Tree Experts at their arboretum near Charlotte, NC. It turns out they study this. After our meeting, our solution ended up with using a 3" stainless deck screw with a star head, two stainless washers and a stainless spring. Every couple of years you back the screw out to relieve the compressed spring due to the tree growth.

  • The spring is a great idea to allow growth and give your sign a nice offset from the tree. – Erik Mar 18 '16 at 15:39
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The right answer will depend vastly on how fast the trees grow. For example Aspen trees grow extremely fast in certain climates while subalpine fir are pretty slow growing in almost every case. Fortunately, there is an extremely easy way for you to find out the growth rate of your trees. Cut one down, count 10 years worth of rings and measure the distance between them. (As a mathematician I really can't support the math behind this, but it'll probably work.)

Take the expected lifetime of your sign, divide by 10, and multiply by the distance you measured. This'll give you the distance the nail should stick out of the tree. Add a couple of inches so the nail won't fall out and you're golden.

For example if your signs were going to be good for 50 years and the distance between the rings for the last 10 years was 1 inch you would need 5 inches of nail sticking out.

(Note) I'm not sure this is the best way hang signs from trees, but it is the answer to the question asked. I'm pretty sure that dkippers answer is a better idea in practice.

  • Thanks for trying to help, but this is not what I was asking. I want the signs to move outward with the tree as it grows. The question is how to attach to allow that. If the nail is really solidly in the tree, then the growth pressure can't push it out. Not solid enough, and the sign will come off on its own from wind, freeze/thaw cycles, etc. As I said, I expect the tree to grow several inches in radius over the life of the sign. I don't want nails sticking out that far. – Olin Lathrop Mar 16 '15 at 21:18
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    If you don't want the nails to stick out that far you need to use a different method. (Probably one without nails at all.) Nails which don't stick out as far as described will be absorbed into the tree, there isn't a fix for that. – Joe Manlove Mar 17 '15 at 4:25
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Use a finish nail; the undamaged sign will slide off sometime in the future when it has long been forgotten, and the tree will have the smallest wound. I have watched a 16d galvanized finish nail, two inches proud, hold a painted tin can lid to a slow-growing tree for at least a couple of decades. Aluminum sounds like an even better material, if a long enough shank can be found.

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Punch a hole in each corner of the sign. Run a length of 1/8" elastic around the tree and the top 2 holes, and again around the tree and the bottom 2 holes. Tie a rolling hitch behind the tree for each cord, leaving plenty of extra length. Loosen the cord as needed.

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Why to put nails in the trees when you can paint the trail signs on them? I know, I know, it needs some updating each 2-3 years, but plastic and aluminium colors may also fade.

I would consider one information board at the beginning of the trail(s), telling where each sign and direction leads, and then just paint them on the tree along the trail.

trail signs trail signs painted on trees

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Painted wood with 2 galvanized nails like this:

Signs attached to trees

They do that all the time in Finnish natural parks and such signs can take all the 4 seasons with minimal maintenance.

The tree will push the sign outwards as it grows but they won't drop out like ever.

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