A good tree fertilizer contains micronutrients including iron, sulfur, copper, cobalt, magnesium, manganese, molybdenum, and zinc. The concentration of these nutrients has a tremendous effect on plants, so proper formulation of fertilizer is vital. A low concentration of salt is also important since excess salt can damage most plants. While using the right concentration of fertilizer is important, it is also important to use the right type of fertilizer. Fertilizer is available in liquid and in granular forms.
Liquid fertilizer is absorbed quickly by the roots.
Delivering liquid fertilizer directly to the roots is especially beneficial to trees that are suffering from a drought. An additional benefit of liquid fertilizer is that pumping liquid into the ground causes aerification of the soil, which provides additional benefits to the surrounding plants. Granular fertilizers are coated to decrease solubility, allowing the nutrients to be absorbed for a longer period of time. Fifty percent of a tree's surface area is under the ground. This hidden portion of the tree is frequently neglected.