Washers should be seated on the wood, not deep in the wood or on the bark. Cables should allow tree to move slightly. Leave to professionals. Before you fertilize or consider treatments for microelement problems, have a soil test done. Your tree may require soil acidification before fertilization, or treatment of microelement problems.
Fertilizers add elements essential for healthy growth.
Trees get their energy from the sun. Leaves and needles trap energy in a molecule of sugar. Sugar is tree food. Keep leaves and needles healthy by timely treatments so trees can get their food. Keep soils free of compaction so roots can get water and essential elements.