Plant fertilizers provide the nutrients that plants need for proper growth and functioning. They may be organic (produced from the breakdown of compost or animal manure) or inorganic (also called commercial or synthetic fertilizers). Inorganic fertilizers contain varying amounts of nutrients, depending on the formula, and are labeled with number designations such as 10-10-10 or 10-20-20. The numbers represent the fertilizer's primary macronutrients in a standard order referred to as the NPK (nitrogen, phosphorus and potassium) number. A 10-10-10 fertilizer, for instance, has equal amounts of nitrogen, phosphorus and potassium. Fertilizer needs of plants vary depending on the crop and its growing conditions.
Nitrogen (N) is important for photosynthesis and promotes green, leafy growth. Fruits and vegetables require various amounts of nitrogen, depending on the crop. Lawn fertilizers contain an abundance of nitrogen and will promote leaves at the expense of blooms when used on flowering plants. Symptoms of nitrogen deficiency include chlorosis (yellowing of leaves) and slow or stunted growth.
Phosphorus (P) is needed for the development of roots, flowers, seeds and fruits. Systems of phosphorus deficiency include premature fruit drop, slow growth and reddish or purplish coloration under leaves and on stems.
Potassium (K) is important for healthy stems and disease resistance. Potassium deficiency results in poor root systems, susceptibility to wilting and wilt diseases, leaf tip and marginal browning, and leaf curl.
Calcium (Ca), magnesium (Mg) and sulfur (S) are secondary macronutrients. They are necessary for healthy plant growth but considered secondary to nitrogen, phosphorus and potassium, since they are generally applied in lesser amounts.
Micronutrients are the remaining elements needed for plant functioning, including boron, chlorine, cobalt, copper, iron, manganese, molybdenum, sodium and zinc, according to Washington State Department of Agriculture.