Junebug
I'll move this thread to the Ask an Arborist area.
Deep root feeding is like so many other things people do to trees ... is it necessary? Like many people prune and cut trees, seldom for the trees good but for their fetishes.
Over fertilizing trees or with the wrong fertilizer as mentioned above can also spell trouble. One of the illusions we fall to is that when a tree is lush and green and booming on with growth ... it's healthy right? Not so.
Trees generally will put off defending themselves from pests and diseases over growing ... that's their code, grow more to get more light and the biggest tree of the forest succeeds where the smaller ones get shaded out.
Too much nutritional value could see trees with over extended structure, heavy foliage and possible more bugs.
Whilst the decompaction and aeration of the soil in compacted areas is beneficial so is good soil care, which means building and providing a good microbial soil with worms, beneficial fungi etc (mulch is the best).
So, what is going in the ground is important. In most cases some Seasol/fish style product benefits as does some organic matter perhaps liquid blood/bone. Keeping down the nitrogen (n) will also prevent rapid growth and lush foliage.
So, knowing what the tree needs (if anything) and knowing what the soil is deficient in are the beginnings of the project. But what you will usually see is a "one size fits all" approach to this.
For instance, the trees leaves are showing some yellowing so landscaper deep root feeds and has a higher N product. The tree improves slightly however you notice a sap sucker infestation developing. Under closer analysis what we discover is the soil was out of the Ph range needed for the tree to take up nutrient that was already present so we added and watered in lime and the tree is fine.
