This is an area of great confusion and misunderstanding. It would seem that to "feed" a tree is important and should be done. Not always true. In fact, most mature trees do not need fertilization. What is important, is to understand when fertilization is helpful and when it is not a good idea.

First off, most mature trees, in a normal growing environment, don’t need additional nutrients in the soil. There are always exceptions, but know why you are fertilizing.

Exceptions on mature trees can be; poor growing space, knowledge of very poor soil, trees that need additional fertilizer due to being planted in the wrong soil type , fruit trees, and sometimes, weak trees.

However, knowing that information, here are some important facts that can cause damage to your tree if you fertilize. Some trees are highly susceptible to leaf and twig insects. Lots of rapid growth from fertilization can attract more insects. Another factor that many people don’t think about is that overly fertilized trees can grow faster than the limbs that support the new growth. Fast growing trees can also self destruct! There is an optional rate of growth of new wood to growth of new foliage. One supports the other and the relationship and balance between the two is important. Wind plays another factor in a tree that may become too heavy too fast. Rain is also a contributor to the added weight on a lot of new foliage.

There are some situations where rapid growth can be a good thing. Pine trees infested with beetles might benefit from rapid new growth to possibly overcome the insects.

Japanese Maples with Tip Blight or Pears with Fire Blight also might grow fast from fertilization, to possibly overcome the disease. These are theories that are possibly true, but if a tree is on it’s way out, one might as well try fertilization. In the same breath, I will say that I have seen trees in the last stages of life, fertilized for no good reason. If the foliage on a pine tree is turning brown, fertilizer will not turn it back to green. If the upper canopy of a tree is in the full stages of dieback, then fertilization may cause suckers to grow along the trunk, but the upper limbs will not recover.