For decades, the accepted solution to protect tree wounds sustained during trimming was to use pruning paint or pruning sealer. These products were applied to open wounds to seal them up and protect the tree. But does this concept really work?
This article will investigate whether pruning paint actually works, examining why this solution was accepted for so long and what modern research has revealed.
What is pruning paint for trees?
From our perspective as humans, our first instinct when we accidentally cut ourselves is to cover the injury. We do this to prevent the wound from getting infected, which leads to serious health problems. And for many years, we applied this concept to trees as well.
When some gardeners or arborists cut or trim a tree, they cover up the wound with various products known as
pruning paint or pruning sealer. These coatings were designed to seal up the open wounds on a tree to prevent it from becoming infected with diseases or fungi or infested with pests.
These kinds of products are usually sold as pots of pruning paint or as cans of sealant that are sprayed on the exposed bark of the fresh wound.
Does pruning paint work?
But does pruning paint actually work? The majority of modern studies say no.
Most research indicates that pruning paint may actually do more harm than good.
The main reason for pruning paint’s ineffectiveness stems from the ingredients used to make it. Most pruning paints are made from petroleum-based components like asphalt. These compounds are used to seal the wound, preventing water from entering the tree.
The problem is that this can also seal in any moisture that was already present on the wound. Pruning sealer also traps any bacteria, diseases, fungi spores, or insects that may have found their way onto the wound. This leaves the tree defenceless against these invaders.
Man-made pruning sealer also inhibits the natural healing mechanisms of the tree. Trees don’t heal the same way that humans do. Instead of repairing the damage, which takes a lot of energy, the tree isolates the wound. It then releases specialised cells that contain the damage and prevent it from spreading to the rest of the tree, forming a natural protective seal.
Any wound sustained by a tree will be present forever but will be contained in a type of stasis to prevent it from causing any more harm. Applying chemical seals to the affected area before the tree has a chance to compartmentalise the wound runs the risk of interfering with the tree’s natural healing process.
Another problem with pruning paint is that these chemical seals will eventually break down way before the tree itself dies. This effectively reopens the wound to the elements, allowing disease and other problems to infect the tree anyway.
What to do instead of using pruning paint
The effectiveness of pruning paint and other products was first questioned by American biologist Alex Shigo, who worked for the United States Forest Service, as early as the 1970s. Shigo’s research showed that pruning paint impairs a tree’s natural healing mechanisms rather than helping.
Rather than continuing to hamper trees with these products, Shigo and other researchers advocate simply leaving a tree to heal itself once it has been trimmed. Trees have been dealing with wounds for millennia before pruning paint came along.
The other thing that arborists and gardeners can do is to use correct pruning techniques. Correctly trimming a tree helps to minimise the amount of damage caused. This involves making clean cuts at the right angle to help stimulate the branch to regrow.
To allow the tree to compartmentalise any wounds properly, never cut into the collar of a branch. This section contains the specialized cells that allow the tree to naturally isolate and seal off the wound from the rest of the tree.
If trimming away diseased branches, make sure to sterilise any cutting tools in between cuts to prevent accidentally spreading the pathogens further.
