The Great Sealant Battle

Finally, a good debate on BonsaiNut with just the right amount of flame to make the discussion toasty but not rude. I avoided this for a long time, but I finally weighed in today. You can find the whole massive thread HERE.

My contribution:

Quote from king kong:

A page of information Mr. Pall and you still have no answer to Dr. Shigo's finding. "All trees will be infected after wounding" "So long as new parts are formed exceed the amount of wood being invaded, the tree will live". If I injured my hand and my Doctor told me this I would checking my calender to see if it was April first. Who cares about compartments. I have no rot fungus for the tree to contend with. Zero fungus do you understand? What is there so hard to understand? Dr. Shigo's work on sealants is based on a condition that does not exist in my back yard. There are no microorganisms having picnics and parties under my wound dressing of pine tar"

KK

I think the reason you aren't getting any real responses to this question is that no one is quite sure what you are asking. After seeing it now several times, I think I now understand, especially with your addendum about no microorganisms in your backyard.

"So long as new parts are formed exceed the amount of wood being invaded, the tree will live"

I think we can all agree this is true. We see it all the time, and Walter has expanded this to bonsai as well as to landscape. The entire center of a tree can be hollow and the tree lives, sometimes with on a 1/4 inch thick 'trunk' circle. The living parts of the tree are intact and continue to grow. I have several completely hollow trunked bonsai. The only concern is stability as Walter points out.

Before parsing out the quotes further, let me digress and further complicate the issue of 'rotting'. Most folks are not clear about disease and 'rotting'. Rot and disease, if I can use those two common terms are not the same thing biologically and are normally caused by different species of microorganisms or fungi. Disease is caused by pathogens. Pathogens live by attacking [I][B]live[/B][/I] wood. Rot is caused by non pathogenic fungi and other benign microorganisms and feed on [I][B]dead[/B][/I] wood. These are composters. Nearly all the interior wood of trees is dead. It serves no purpose other than for stability and water transport.

Having pathogens attack a tree through a wound, any wound is serious business and threatens the life of the tree because it does attack the living portions of the tree. Fortunately, this is an exceedingly rare event relative to rotting of dead wood by composters. For most bonsai applications you can just forget about it. If you want to be super careful, you can disinfect your tools between every cut and disinfect every cut with a spray of disinfectant. It may or may not work. The best defense against plant pathogens is keep them out of the area and to reduce environmental conditions that favor their growth. This should not be confused with the action of composters, of which we are trying to deal with in using cut paste.

"All trees will be infected after wounding"

Although it isn't entirely clear from the short excerpt, I believe that Dr. Shigo is referring to composter (non pathogenic) rather than pathogenic species, although I can see a case for lumping the two together. Unless the sealant is also an effective disinfectant, simple drying of the wound might be a better defense than sealing the pathogen in. If we consider composters only, one must consider how difficult it is to kill to some of these. Some fungal spores are notoriously difficult to kill. Just consider what it takes to keep composters out of the canning of fruits and vegetables. These can survive several minutes of boiling temperatures. So, I cannot see how it is possible to 'seal out' non pathogenic composters, even if you disinfect a wound, nothing short of autoclave temperatures could achieve that. Even good disinfectants like bleach and methanol are only going to reduce but not eliminate the population in such a 'dirty' environment. So, it is in this context that I think Dr. Shigo is making these remarks.

I do understand your comment about not have "rot fungus" in your backyard. In light of the above, if you mean pathogenic species, you are probably correct, most of us don't have these, or at least not in the number of environmental conditions conducive to attack. If you mean non pathogenic species (composter) than you are most certainly wrong. Composters are virtually everywhere on earth. Nothing would decay or rot without them. In Florida you have a bonanza of composters, and I do not believe you can possibly keep them out with any sort of sealant.

As to whether or not the decay process of the dead inner wood will occur faster or slower with a sealant, I believe there are too many parameters to really make a broad generalization. Clearly, it is species dependent and environment dependent. I personally do not use sealants and believe that the effort of using them in[I] my situation[/I] is clearly not justified. I believe this to be true  for most containerized ornamental tree growers. It has been clearly demonstrated to be true in landscaping and orcharding.

Understanding the physiology of tree growth can give you better tools for handling wounds than sealants. I don't see how this can be disputed. As an example, if you want maximum growth of scar tissue and minimum recovery time, there are a couple simple things you can do. First is to NEVER remove the collar tissue when removing a branch. The first thing you should do is to identify this feature and make sure you don't disturb it. Collars are the tree's way of diverting the growth pathways around a branch. Remove a branch and leave the collar and the upper and lower parts of the tree are basically unaffected from a health standpoint. It will just keep on doing what it has been doing and callus tissue will quickly grow over the wound eventually sealing it except for a tiny hole. Secondly, when removing a large branch, leaving the collar intact, you want to maximize growth in the area of the collar. You do this by leaving a sacrifice branch directly [I]above[/I] the collar. This will 'pull' vast nutrients through collar area and increase the growth of the callus. Of course the sacrifice has to be removed too at some point.

The other issue is trunk chops, about which I have changed my mind over the years. In a trunk chop, you are doing the reverse of branch pruning and leaving a collar is not possible except that should you cut back to a lower smaller branch, you should be careful not to disturb the collar of the branch. This is actually my preferred method since it foster faster healing and give you an insurance policy on the tree's survival. In any case, there is still the cut of the main trunk with which you must deal. Formerly I recommended a diagonal cut approaching the final desired shape. I no longer do that. When you make a cut that does not involve collar material, you will indeed get dieback down the trunk. It varies with species and vigor, but you will get dieback. This usually takes the shape of a V or U down the trunk beneath the cut. When you make a diagonal cut, you just guessing how much dieback there will be. Sealants are probably not going to change this, at least to any great degree. A [I]much better[/I] solution is to cut higher, making a perpendicular cut across the trunk. Wait a year and then go back and find out where the tree has decided to dieback, that is where compartmentalization has place. Then you can go back in and carve down to the live tissue which will the beginning of a new collar forming. You can leave a stub or carve a feature for large cuts or crater it out a bit to heal it over more smoothly. Either way you substantially reduce the risk.

You can get very creative with this. Jim Gremel (who does use cut paste) carves out large Cedar branches down to the collar, but leaves a stub about the [I]size of a branch that would have been proportional for the finished tree[/I]. He lets the callus roll over to this stub and creates a totally natural feature of the right size.

I personally don't fight this sealant battle anymore. In the vast majority of cases, I don't think it does anything, but if it makes you feel better, fine. In bonsai, I don't think there is much of a downside either. But clearly, it helps to know all the facts and principles and I hope that I have helped to achieve a bit of that here.

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