Caution should be used in applying slow-release fertilizers around trees and shrubs because they may keep the plant growing late in the summer. Late-season growth may not harden off completely and excessive winter damage may occur. The major reason for buying a fertilizer combined with a pesticide is convenience. The problem is that the timing for a fertilizer application often does not coincide with the appearance of a disease or an insect problem. The type or form the fertilizer comes in is called the formulation.
Soil type dictates the frequency of fertilizer application.
Sandy soils require more frequent applications of nitrogen and other nutrients than clay-type soils. Other factors affecting frequency of application include the plants being grown, the frequency and amount of irrigation, the type of fertilizer applied and its release rate. Root crops require less nitrogen fertilization than leafy crops. Corn is a heavy nitrogen-feeder, while most trees and shrubs perform nicely with one good application every year. It is important to group plants with similar fertilizer needs close together to avoid improper rates of application.