Tree Fertilization – The Pros and Cons of Fertilizing Our Trees


Many of the larger tree care companies offer tree health care along with their list of surgical methods. Tree health care is a very valuable service for those who truly care about their trees and want to keep them healthy in spite of problems that they may encounter as a result of being in an urban or suburban setting. The methods used by professional arborists in the practice of tree health care come as a result of scientific studies in botany, horticulture, agriculture, and arboriculture. Brilliant minds in universities with the time and resources to study plant life on the cellular and molecular level have given information to practicing arborists that, when applied correctly, can save and extend the lives of trees.

It’s good to know that there are health care solutions for the problems that sometimes plague our beloved trees. But just because it’s labeled “plant health care,” and is administered by a man in a green uniform does not really mean that it is the right way to go. Plant health care, just like human health care, requires both scientific research for the development of the medicine and qualified and well-studied practitioners to administer the medicine in the right way. We know that the science is there. Sadly, what is often missing in both cases is the well-studied practitioner.

Have you noticed that there is an over-use of medicines that were developed to treat human medical conditions such as attention deficit disorder and depression? The over-prescription of these drugs is an indisputable fact. The social scientists who discovered and studied the conditions also noted the percentage of the population that is afflicted. Medicine is prescribed to a percentage of the population, in some cases, that is 100 times greater than the number with the disorder. There is no doubt that the medicine helps those with the disorder, but what does it do to those who are not afflicted? This is a question worth discussing in another forum.

In the case of our trees, have you noticed that the usual prescription for a problem in trees is deep root fertilization? Why would this be? I have witnessed arborists actually prescribe and sell fertilization before testing the composition of the soil that they are fertilizing. This is a classic example of medicating without diagnosing. The fact that an arborist would add something to the soil suggests that something is missing in the soil. The only way to know this is to test it in a lab. The real question (besides the obvious issue of wasting money) is what harm may be done if we fertilize a tree that does not need it? Let’s talk about that.

In a way, fertilizer is to trees as steroids or growth hormones are to humans. It encourages growth and vitality. It also tends to mute or turn off the natural defenses that an organism has to disease. Like humans and animals, trees react to invasion by turning on their own immunodefense. Fertilizers can sometimes “trick” a tree into vitality. In the process the tree stops or slows production of chemicals on a cellular level that combat the invasion of pests and disease. So, in spite of an outward appearance of health, the parasite that is causing the problem is allowed to grow unfettered by the tree’s immune system.

If the diagnosis of the patient (human or tree) is that it is lacking in nutrients, then it is helpful to apply fertilizer as treatment. But without this diagnosis, fertilizer as a treatment is just malpractice. If fertilizer is suggested to you by an arborist upon his first visit to your property, you should be careful. He may be prescribing the only treatment that he knows or is willing to apply. A good arborist – one who is truly committed to tree health care – will spend time on the diagnosis so that the treatment fixes the problem.

Let’s not be afraid to ask health care professionals (arborists and doctors) what exactly is causing the problem. We shouldn’t take pills unless we know that we have a condition that the pills are treating. And we shouldn’t apply treatment to trees unless we know that they have a condition that the treatment cures.