There are essential elements for plant growth and success, in addition to sunlight, oxygen, carbon dioxide, soil and water they also require mineral nutrients. These nutrients are normally absorbed from the soil, but not all soils are mineral rich or they may not contain the needed quantities. There are 14 mineral nutrients required for healthy growth; nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), sulfur (S), chlorine (Cl), iron (Fe), boron (B), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo) and nickel (Ni). N, K, Ca, Mg, P, and S are considered macronutrients, and Cl, Fe, B, Mn, Zn, Cu, Mo, and Ni are micronutrients. The terms micro and macro refer to the amounts needed of a specific nutrient, not to its importance in physiological processes or health.
Categories of nutrients are further divided; primary macronutrients are nitrogen, phosphorus and potassium and are required in the largest amounts, secondary macronutrients comprise calcium, magnesium and sulfur. Although the secondary macronutrients are required in smaller amounts it does not decrease their importance or necessity. Micronutrients are required in far smaller amounts, relative to the macronutrients these (zinc (Zn), iron (Fe), manganese (Mn), copper (Cu), boron (B), molybdenum (Mo), and chlorine (Cl)) are needed only trace amounts. Typical concentrations for plant growth are provided in the table below:
(After E. Epstein. 1965. “Mineral metabolism” pp. 438-466. in: Plant Biochemistry (J.Bonner and J.E. Varner, eds.) Academic Press, London. )
The important takeaway is that the labels “micro”, “macro”, “primary” and “secondary” all refer to amounts, and is not reflective of their value to the plant. Amounts of micro and macronutrients required may be different depending on the season, when buying fertilizer pay close attention to the amounts as well as any indication of when to utilize that product. For the best results consult with your arborist, they can perform a soil analysis and identify exactly which nutrients are lacking or deficient. Then your arborist can develop a customized fertilization regime, tailored precisely to the needs of your landscape plants.