Why Fertilize Landscape Trees?

A Technical Report from The Bartlett Tree Research Laboratories

Trees and shrubs require 17 different elements. If they lack one or more of these nutrients, the tree may become less healthy and more susceptible to pests and other problems. Nutrient deficiencies occur for a number of reasons in the urban environment. Most new construction starts with the removal of topsoil from the entire building area. This means that when the landscape is planted at the end of construction, the plants grow into low nutrient subsoil. On established sites, the annual removal of fallen leaves reduces the level of nutrients that are returned to the soil whereas in forest conditions, fallen leaves would break down releasing nutrients to the soil. Nutrients applied to turf grasses are not always beneficial to trees. Turf requires a higher pH than most tree species, so annual lime applications may be detrimental to trees surrounded by turf. Fertilizer should be applied only when there is a known deficiency. Readily available and reliable laboratory soil and foliar nutrient analyses are superior to visual analysis of leaf color and twig growth at detecting deficiencies and the underlying causes of some deficiencies (e.g., soil pH). Lab analyses can also detect secondary element (e.g., Ca, Mg, Mn) deficiencies or excesses that are overlooked with visual analysis.