Our Tri-blend is a mix of Save A Tree (Thrive in Zamzows stores), Worm compost tea and a fertilizer mix made by Dr.Brennan for these Boise area soils.
This takes a special type of equipment and the ability to oxygenate the living organisms in the tank when it is being brewed over a three day period...a bit of a time burner but well worth it...just look at our trees :)
This system uses a diaphragm pump which provides 60 psi of pressure. As the probe goes into the ground the fertilizer is injected laterally at that high pressure which helps fracture the ground and push the material in a more even pattern throughout the root structure.
If you use a system like this you do not need as much material because you are not losing so much from being tied up in the organic material at the surface or competing grass roots above the tree roots.