I have three 20 year old Japanese white spire birch in three raised 40"...
I have three 20 year old Japanese white spire birch in three raised 40" x 70: boxes next to each other and 1 to 3 feet above ground (see attached photo). Rainbow Treecare has proposed applying Maintenance Rootcare Fertilization with 3 Macronutrients & 8 Micronutrients. Lasts for About Two Years for $182. I definitely want to do what I can to keep the trees, but $182 sounds like a lot. It particularly seems a lot since Rainbow indicates it is applying the fertilizer to 400 sq ft and shows a diagram in which the fertilizer is applied in a large circle around the tree. There is no way to do this with the boxes. Can I do something just as good for the trees myself, probably applying the fertilizer just in the boxes and if possible using spikes or something so that I only have to do it once or twice?
Fertilizing inside the boxes will only aid the plants growing there, trees feed at the drip line and possibly beyond. The tree care company is correct, see http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/tree-fertilization-guide/#when-to-ferti... for much more information. Using spikes make the user feel well while root feeding is better for the tree.
On one side of the row of boxes is the neighbor's yard and on most of the other is pavers. Would you recommend feeding at the drip line in what will an uneven way? We can probably do 180 degrees to the east with the neighbor's permission but only maybe a total of 60 hit and miss degrees to the west.
It is what it is, meaning you can only work with what you have and some is better than nothing. I have found several sources telling me that mature shade trees need not be fertilized at all unless they are showing problems. I know this is not what tree services want to hear but after all they are in business.