Fertilizing trees and shrubs in your landscape is not necessarily an annual ritual. Many gardeners have the false impression that the more fertilizer they apply the more the plant will grow. Fertilizer is not plant food. Plants use water, carbon dioxide, elements from fertilizer, and energy from the sun to produce their own food. Synthetic (manufactured) and natural (some times incorrectly called organic) fertilizers provide nutrients for plant growth.
Addition of the correct amount of fertilizer can promote healthy flower production and foliage growth while an excessive fertilizer application can decrease plant health and can lead to decline and death. Over application or incorrect application of fertilizer can contribute to polluting our rivers, streams, lakes, and estuaries. Excess fertilizer can increase the likelihood of some plant diseases. Fertilizing plants that have already outgrown their allotted space can only lead to more pruning. A moderate rate of growth and good, green color is desired for most woody plants. Excessive vigor, which is evident by lush, green leaves and long shoot growth is often undesirable. Such plants are more susceptible to injury by cold in winter, are more likely to be broken during wind and ice storms, and usually will require more pruning than plants making moderate growth.
All too often gardeners assume that if a plant is not doing well they should fertilize to correct the situation. Fertilization may be helpful but only after the problem causing poor growth has been corrected. Plants which are growing poorly will exhibit one or more of the following symptoms:
light green or yellow leaves
leaves with dead spots
leaves smaller than normal
fewer leaves and/or flowers than normal
short, annual twig growth
dying back of branches at the tips
wilting of foliage
These symptoms of poor growth may be caused by inadequate soil aeration, moisture, or nutrients; adverse climatic conditions; incorrect pH; or disease. Recently transplanted trees and shrubs often will not resume a normal growth rate until the original root system is reestablished. Plants disturbed by construction within the past five to ten years may be in shock and exhibit limited new foliage growth. Do not assume that an application of fertilizer will quickly remedy any problem which is encountered, in many cases it can make existing problems worse. You should attempt to determine the specific cause in each situation and apply corrective measures.