Firstly, it significantly reduces the risk of trees accidentally damaging your property. Then there’s also the question of regeneration. Pruning trees promotes new growth, not forgetting the health implications. Pruning trees can be a significant deterrent to pests and prevent potentially damaging infestations and tree diseases.
Should You Seal A Tree Wound?
A pruning sealant is a product touted to assist trees to heal from pruning wounds. There is something comforting about smoothing something viscous over the cut section of a branch or trunk, but does it help? Generally, the answer is no, although there is an exception for using pruning paint for oak trees.
Before you use any tree wound sealer, it pays to find out what the experts have to say on the topic. Read on for an overview.
The Idea Behind a Tree Pruning Sealer
A tree wound sealer is a commercially available product that is applied to the cut section of a recently pruned tree or shrub. In many ways, the idea of applying a tree wound dressing makes sense to a gardener, as a kind of Band-Aid for the plant. But it is usually a bad idea.
When you trim or cut living wood from a tree, you always reduce its potential to photosynthesize sunlight and oxygen into energy. Pruning also creates a wound in the woody plant that requires energy to heal.
Yet the process of pruning is often necessary to form a tree’s branch structure or remove damaged or diseased wood. Since pruning cuts create openings in the wood for insect and disease to enter, it feels helpful to apply a tree wound dressing or sealant after pruning.
Trees Heal Their Own Wounds
Woody plants have been on the planet as long as we have and have developed their own natural defenses. While we think of a tree as “healing” from a wound, a woody plant actually doesn’t heal, but isolates the damage by forming a type of wood over the wound that repels harmful organisms. This is termed compartmentalization.
How does this work? After a tree is pruned, it grows callus tissue at the edges of the pruning wound that moves slowly toward the center of the exposed area. Assuming that the cuts were made carefully and correctly, the new wood slowly expands to cover the entire wound.
This natural process makes pruning sealants totally unnecessary and, in fact, damaging to the tree. Covering wounds with tree wound sealer prevents the oxidative processes from progressing naturally, which slows callus formation. Think of the promotion of these tree sealants as an advertising strategy rather than something to assist the trees.
The only time that painting a tree pruning wound is helpful is when an oak tree must be pruned in spring or summer. Generally, this is to be avoided since oak wilt can enter through the wounds. Painting over the wound with latex house paint is recommended. Winter pruning oak wounds do not require painting.
Why Don’t Arborists Paint Cuts with Wound Dressing?
by: Board Certified Master Arborist, Gilbert A SmithBackyard Wisdom – April/May 2020
Fifty years ago when I was a young “tree skinner” Yes, that’s what they called us and with good reason. I was taught to paint all of the cuts that I made with tree tar. That was the measure of a good job. My father would say, “I saw a lot of ‘white eyes’ in the trees you trimmed today.” What an insult! “White eyes” were the newly exposed round tree cuts that looked like eyes on the branches. If my foreman saw too many of them, then I had to fill my leaky old paint pot, strap it to my tree saddle, climb back up the tree and paint every cut larger than 2 inches in diameter. One good reason we didn’t trim on the way up, but always on the way down, was to avoid touching that sticky black tar from freshly painted cuts as we descended. We believed that paint prevented the tree from rotting. Besides my father and my foreman this was taught by the University of Illinois, the International Society of Arboriculture and the Morton Arboretum.
Forty years ago when I was attending the University of Illinois there was a great debate as to which type of paint was the most effective at stopping rot. So they did testing. Of course they had to have untreated wounds as a control group. Guess which type of paint created the least rot? To everyone’s surprise the untreated cut healed faster with less rot! Oh how the old timers screamed! “I’ve been doing this for 40 years and…. and well you paint the side of a barn to keep it from rotting don’t you?” The old timers had a good point so the US Forest Service and several universities did further testing to find out why unpainted wounds healed better.
The upshot was that trees have been around for a lot longer than we humans with our paint. Trees don’t heal like we do, they do not replace damaged tissue with new tissue. Once a tree is wounded it is wounded for life. To prevent rot their strategy is:
- To dry out so fungal rot can’t germinate as easily.
- Limit nitrogen in their branch wood which makes it harder for microorganisms to degrade and consume them.
- To change cellular structure. Any tree cells near the wound stop what they are doing, fill up with anti rotting resins and physical blocks, such as tyloses. In this way the tree forms 3 walls that inhibit rot.
When we painted the cuts the water was sealed into the wound but within 2 weeks the paint formed microscopic cracks just the right size for the spores of wood rotting fungi to find a happy, moist place to grow.
Further research by Dr. Alex Shigo at the US Forest Research Station revealed that cutting branches too close to the trunks (flush cuts) broke those defense walls that trees have put up to protect themselves. This allows rot to enter the trunks, weaken and make trees more dangerous. Oh how the old timers howled then!
So what did we learn about tree wounds?
- The most important treatment to prevent rot is to know how to make a proper cut. The person who mows your lawn, or maybe your spouse, does not know how to make proper cuts. Their trimming can make your trees more dangerous and much less healthy.
- Do not trim Oaks or American Elms in the summer or you risk attracting fatal Dutch Elm Disease or Oak Wilt. This is the exception to the painting rule: If you have storm damaged Oaks or Elms and you have to cut them in the summer it is mandatory that you paint the cuts to mask the pheromones released and avoid attracting the insects that carry those deadly diseases.
If the trimmer doesn’t know how to identify trees then don’t let them trim. - One of the most damaging things you can do to your trees is to let people trim them with unsterile trimming tools. Fireblight is currently devastating Crab Apples, Apples, Hawthorns, Pears, Serviceberry, Cotoneaster, Mountain Ash, Roses, Quince and many other lovely ornamental plants because unknowledgeable landscapers spread Fireblight bacterium from tree to tree on their diseased infected tools.
You’ll be glad to know that I’m no longer a “tree skinner” but I’ve gone on to become an ISA Board Certified Master Arborist and these are a few things I’ve had to unlearn from the good old days.
Are There Any Exceptions To This New Approach?
If disease is prevalent, then yes. For example, oak trees are an exception because of the susceptibility of oak trees to the disease oak wilt. The disease is spread from tree to tree by Nitidulid beetles which are attracted to tree sap.
Because of this, it is recommended practice to seal cut tree limbs with a wound dressing as quickly as possible before the beetles catch a whiff of that sweet-smelling sap.
A wound dressing can be used in such cases, but ordinary paint works just as well. That said, applying wound solution to pruned branches should only be necessary for the first three or four days after an operation.
In other words, one coat should be more than enough to keep those disease-spreading beetles at bay.
In fact, in the 24 states where oak wilt is a concern, including Texas, pruning is positively discouraged during spring. Considering the lasting damage that can be done by this disease, it’s easy to see why.
When pruning your maple tree, just make sure the pruning shears are sterilized before use.
FAQ
Should You Seal a Tree Branch After Cutting With Wound Paint?
The recommended practice used to be to seal cuts and wound wood in tree sealer. The idea was that pruning sealer would prevent decay and speed up the healing process.
However, more recent research has overturned this idea, and it’s now believed that rather than help, pruning sealers actually hinder the natural healing of a tree cut or wound.
In other words, instead of sealing out, they are sealing in disease and decay, as well as preventing the millennia-old process of self-healing known as compartmentalization.
In most cases, it’s simply best to let trees heal on their own.
How Do You Treat Tree Wounds?
The process of compartmentalization, which effectively stops disease from spreading by containing or compartmentalizing wounds under a layer of cells, allows trees to heal on their own. This process is best left to take its course. When pruning your dogwood tree, it will thank you for not using a sealant afterwards.
See also Pruning Rhododendrons: When & How To Cut Back?
Even though there are a plethora of products as wound “dressings” on the market, they are, for the most part, completely unnecessary.
Should You Paint Over Cut Tree Limbs?
The common consensus is no; you should not. Wound paints and pruning sealers are not only unnecessary to the healthy and safe healing of a tree cut but could also be counterproductive and potentially harmful. This, coupled with the fact that they are not the most eco-friendly of products, means that, for the most part, you should steer well clear.
That is unless you live in Texas and you happen to be pruning an oak. Then, by all means, use pruning paint. It’s either that or running the risk of oak wilt. So you might not have much of an option, save for not pruning at all.
What Is Tree Pruning Sealer?
Pruning sealant is usually petroleum-based, while darker varieties can contain asphalt. As well as being potentially harmful to humans, pruning sealers are thought to hinder the cell regeneration and healing of tree wounds.
Don’t More Natural, Less Harmful Products Exist?
While more natural, less harmful products do exist—made from a variety of ingredients, such as collagen, pectin, aloe vera, etc.—there isn’t any hard and fast scientific proof to support the fact that any of them are actually beneficial to a tree wound.
Final Word on Should I Seal a Tree Wound?
So there you have it—what to put on a tree after cutting a branch. The answer, for the most part, seems to be nothing at all. Remember if the cutting is done at the correct time, and following all the best practices, then trees should self-heal perfectly well without the need for any help.
Your job just got a little bit easier.
