Plants require many nutrients for growth and development of flower and seeds. The macronutrients of nitrogen, phosphorus and potassium are needed in the greatest amounts, while micronutrients are required in lesser amounts to sustain certain plant processes or improve plant health. The nutrients in plant fertilizer are listed on the product label and usually include the percentage by weight each element contributes in the product.
Nitrogen (N) is the element most heavily utilized by plants. In fertilizers, it is the first number listed in the three-part ratio. For example, in the fertilizer ratio 10-15-12, "10" means that 10 percent of the product weight is made up of nitrogen.
Nitrogen is responsible for the rapid greening of plant foliage and is vital in the creation of new plant tissues. A lack of nitrogen causes a slowing of growth as well as yellowing of foliage. In severe cases of nitrogen deficiencies, leaves and stems can be ivory in color with hints of pink.
Phosphorus (P) is a central element required for photosynthesis. In fertilizers, it is the second number listed in the three-part ratio. For example, in the fertilizer ratio 10-15-12, "15" means that 15 percent of the product weight is made up of nitrogen.
Phosphorus is most heavily used in new growth. This element facilitates plant cell formation, division and multiplication, and overall use of carbohydrates by plant cells. For a plant to be vigorous and productive, ample amounts of phosphorus ensure healthy and continual growth. Phosphorus is needed to promote production of cells that become flowers.
Potassium (K) is typically the second-most used macronutrient after nitrogen. In fertilizers, it is the last number listed in the three-part ratio displayed. For example, in the fertilizer ratio 10-15-12, "12" means that 10 percent of the product weight is made up of nitrogen.
Potassium plays a central role in plant metabolism, using its manufactured carbohydrates to fuel important cell processes like obtaining energy from sugars. Gerald Kidder and Sydney Park Brown suggest that potassium also plays a role in photosynthesis, protein synthesis and improved cold tolerance. A lack of potassium can lead to foliage being shriveled or with brown streaks or spotting.
Magnesium (Mg) is a silent macronutrient or vitally important micronutrient. It is not found in large amounts in plant fertilizers, unless it is a specially formulated product designed for treatment of a magnesium deficient soil. Magnesium comprises the center of a chlorophyll pigment molecule, and without chlorophyll, the leaf cannot absorb sun energy to make food sugars. Plants lacking magnesium have yellowing in older or lower leaves in their canopy.
Sulfur (S) is the last of the most important components of plant fertilizers, a nutrient in large amounts in the form of sulfate. Sulfur is a building block used to create amino acids and other metabolism products. The protein that provides the odor to onions and chives is heavily comprised of sulfur. In legumes like beans and peas, sulfur is required to create the root nodules that fixate nitrogen in the soil.
Depending on the fertilizer and its intended use, varying amounts of trace elements accompany the five macronutrients. Seven micronutrients play small but key roles in plant health. Soils that lack one or any combinations of these micronutrients result in plants that have limited growth or stunted performance. Also, the soil pH often affects the availability of these elements for roots to absorb. Concentrations of these trace elements can affect a plant's ability to absorb other nutrients. For example, an over-abundance of iron can limit the plant's uptake of manganese.
These are seven key trace elements that are found in varying percentages in common plant fertilizers:
Manganese (Mn) can be used by the plant as a substitute for magnesium, which gives plants their lush green color.
Iron (Fe) is required for creation of the green pigment chlorophyll.
Copper (Cu) activates enzymes in plants.
Zinc (Zn) helps regulate plant growth rates and enzyme reactions.
Boron (B) needs varies considerably across plant types. It is used to regulate the rate of production of carbohydrates.
Molybdenum (Mo) is needed in extremely small amounts, but without it a plant can have difficulty absorbing and utilizing the macronutrient nitrogen.
Chlorine (Cl) is also used in very minute amounts. This element facilitates the usage of water during photosynthesis.