There are approximately 20 elements necessary or beneficial for plant growth and blooming. Some are derived from air and water - Carbon (C), hydrogen (H), and oxygen (O) - while others are mostly absorbed from the nutrient solutions we provide. Six of the elements that should be supplied in your fertilizer - the "macronutrients" - are used heavily by plants: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). The remaining essential elements, the micronutrients, are required in small amounts only: boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), sodium (Na), zinc (Zn), molybdenum (Mo), and nickel (Ni). Additionally, it appears that both silicon (Si) and cobalt (Co) may play a beneficial role in plant health.
Below is a brief synopsis of the roles the elements from fertilizers play in the life of your plants:
Nitrogen (N) is a major component of proteins, hormones, chlorophyll, vitamins and enzymes essential for plant life. Nitrogen metabolism is a major factor in stem and leaf growth (vegetative growth). Too much nitrogen can delay or prevent flowering, while deficiencies can cause yellowing of the leaves and stunted growth.
Phosphorus (P) is necessary for photosynthesis, protein formation and almost all aspects of growth and metabolism. It is essential for flowering. Phosphorus deficiency - sometimes associated with purple leaves - results in slow growth, poor flower production or premature loss of flowers.
Potassium (K) is necessary for the formation of sugars, starches, carbohydrates, for protein synthesis and cell division in plants. It helps to control water absorption and loss, improves the physical sturdiness and cold hardiness of your plants, and enhances flower color. Too little potassium can result in mottled, spotted or curled leaves, or a burned look to the leaves.
Sulfur (S) is a structural component of amino acids, proteins, vitamins and enzymes and is essential to produce chlorophyll, so a deficiency usually shows up as light green leaves.
Magnesium (Mg) is a critical structural component of the chlorophyll molecule and is necessary for functioning of plant enzymes to produce carbohydrates, sugars and fats. Magnesium-deficient plants show yellowing between veins of older leaves, and they may appear limp.
Calcium (Ca) plays a role in the functioning of enzymes, is part of the structure of cell walls, helps control the water content of cells, and is necessary for cell growth and division. Some plants must have calcium to take up nitrogen and other minerals. Calcium, once deposited in plant tissue, cannot move to other plant tissues, so must be supplied regularly. Without a sufficient supply of calcium, your plants may display stunted or stopped growth. Other possible symptoms include distorted new growth, black spots on leaves, or yellow leaf margins. Recent studies indicate that calcium apparently plays a much bigger role in plant health than previously thought.
Iron (Fe) is necessary for enzyme functionality and is important for the synthesis of chlorophyll. It is essential for young, actively growing tissues. Iron deficiencies are indicated by the pale color of young leaves followed by yellowing, and large veins. An adequate supply of soluble iron in the plant nutrient also inhibits the formation of phenol compounds, which can kill roots.
Manganese (Mn) is involved in enzyme activity for photosynthesis, respiration, and nitrogen metabolism. In young leaves, a deficiency may be indicated by a network of green veins on a light green background similar to that seen in an iron deficiency. Dark spotting may occur near the veins. In extreme cases, the light green parts become nearly white, and leaf loss may occur.
Boron (B) is used in cell wall formation, for membrane integrity within cells, for calcium uptake and may aid in the transfer of nutritional sugars between plant parts. Boron affects a variety of plant functions, including flowering, pollen germination, seed development, cell division, water balance, and the movement of hormones. Boron must be available throughout the life of the plant as, like calcium, it is fixed in the plant once absorbed. Deficiencies can lead to very stunted or irregular growth, with leaves that are thick, curled and brittle. Roots can become discolored, cracked and covered with brown spots.
Zinc (Zn) is a component of enzymes or as an important aid in the functioning of them, especially auxins, the plant growth hormones. It is essential to carbohydrate metabolism and protein synthesis. Deficient plants have mottled leaves with irregular chlorotic areas. Zinc deficiency leads to iron deficiency causing similar symptoms.
Copper (Cu) is concentrated in roots of plants and plays a part in nitrogen metabolism. It is a component of several enzymes and may be part of the enzyme systems that use carbohydrates and proteins. Deficiencies can result in the die back of the tips of new growths.
Molybdenum (Mo) is a structural component of the enzyme that reduces nitrates to ammonia. Without it, the synthesis of proteins is blocked and plant growth ceases. Seeds may not form completely, and nitrogen deficiency may occur if plants are lacking molybdenum. Symptoms may include pale green leaves with rolled or cupped margins.
Chlorine (Cl) is involved in osmosis, the ionic balance necessary for plants to take up mineral elements and in photosynthesis. Deficiency symptoms include wilting, stubby roots, chlorosis (yellowing) and bronzing. Flower scent may be decreased.
Nickel (Ni) is required for iron absorption. Plants grown without additional nickel will gradually reach a deficient level at about the time they mature and begin reproductive growth. If nickel is deficient, plants may fail to produce viable seeds.
Sodium (Na) is involved in osmotic (water movement) and ionic balance in plants (much as it is in people).
Cobalt (Co) is required for nitrogen fixation, so a deficiency could result in nitrogen deficiency symptoms.
Silicon (Si) is found as a component of cell walls. Plants with supplies of soluble silicon produce stronger, tougher cell walls making them more heat and drought tolerant. There is also some evidence that silicon plays a role in the prevention of fungal infections in the case of tissue damage.