Soil tests need not be run every year, but follow-up tests every three to five years may be necessary to monitor fertilization practices. Phosphorus and potassium remain in the root zone until the plant uses them, while Nitrogen, depending on its form, could be volatile, or leached out of the root zone, or taken up in large amounts by the plant. Thus, one may need to replace this element every year in moderate amounts. However caution should be exercised in applying nitrogenous fertilizers. Nitrogen, in excess, can be harmful, and result in plant burns, or encourage weak, fast growth.
Fertilizers are available in commercial inorganic or organic forms.
Choice is strictly a matter of personal preference as both types of fertilizers have distinct advantages and disadvantages. However, cost of the material and ease of handling are usually prime considerations in selecting the respective fertilizer type. Organic Fertilizers Organic materials such as manures and composts are highly desirable for gardens. They supply necessary plant nutrients and improve soil structure, tilth, aeration and water holding capacity. For clay soils, long-fibered materials such as straw could be used to improve the soil, but in sandy soils, materials with more humus, such as peat or rotted saw dust, would be advantageous.