Every plant, like any organism, needs certain components for growth over and above fertilizer, sun, rain, and air. Plant nutrition is a term that takes into account the interrelationships of mineral elements, biostimulants, and organisms in the soil or soilless solution as well as their role in plant growth. The term "nutrition" refers to the interrelated steps by which a living organism assimilates food and uses it for growth and replacement of tissue. Previously, plant growth was thought of in terms of soil fertility or how much fertilizer should be added to increase soil levels of mineral elements. Most fertilizers were formulated to account for deficiencies of mineral elements in the soil. The use of soilless mixes and increased research in nutrient cultures and hydroponic techniques, as well as advances in plant tissue analysis have led to a broader

A plant is a plant. By current standards, all plants use 16 primary or essential elements to grow, albeit in different concentrations. The term essential mineral element (or mineral nutrient) was proposed by Arnon and Stout in 1939. They concluded three criteria must be met for an element to be considered essential. These criteria are:

1. A plant must be unable to complete its life cycle in the absence of the mineral element.
2. The function of the element must not be replaceable by another mineral element.
3. The element must be directly involved in plant metabolism.

These criteria are important guidelines for plant nutrition but exclude beneficial compounds, such as amino acids, carbohydrates, enzymes, etc. and beneficial mineral elements. These include minerals that can compensate for toxic effects of other elements or may replace mineral nutrients in some other less specific function, such as the maintenance of osmotic pressure. The omission of beneficial compounds and minerals in commercial production could mean that plants are not being grown to their optimum genetic potential but are merely produced at a subsistence level. This is one of the major blunders associated with the industrial commercial agricultural revolution that accompanied the Industrial Revolution in the late 1800's. By assuming plants only need a finite number of materials to grow, farmers neglected the benefits of myriad other compounds and biological materials towards plant growth in soil. They essentially brought hydroponic fertilization (salt or synthetic based) into the soil zone effectively locking out beneficial biological systems. This miscalculation is prevalent in our farming today and is just now being augmented by organic farming in the mainstream.

There is a common misconception that what a plant "eats" in a hydroponic or soilless scenario is somehow different from what a plant "eats" in soil. The truth is that a plant has evolved over millions of years to the point that it uses certain aspects of its environment for its growth. With the understanding of these respective plant requirements and environments being furthered everyday by the scientific community and the increasing collective education of the public regarding these concepts, it is possible to provide specific materials to enhance specific plant processes on a commercial and individual level. For example, a plant utilizes more Nitrogen in the vegetative stage and more Phosphorous in a flowering stage. This phenomenon is apparent in the formulation of complete fertilizers used in a hydroponic or soilless scenario with "veg" fertilizers emphasizing Nitrogen and "bloom" fertilizers emphasizing Phosphorous, generally. The ability to bring a full spectrum of nutrients in a pre-calibrated fashion allows the grower more control and, in turn, potentially higher yields.

Function and Sign of Deficiency of the Essential Elements
It should be noted that this spec analysis is only a start and that a plant can only respond to stress and deficiency in a handful of ways. For example, having an HID light too close to your plants can cause leaf curling, overwatering can cause yellowing, etc. If growing indoors, before you try and correct what you think is a mineral deficiency troubleshoot your environmental conditions. However, deficiency can still be experienced using complete fertilizers so listen to your plants.

Sub category navigation:      Macronutrients          From Air and Water          Micronutrients          Others

Macronutrients

1. Nitrogen (N): Part of a large number of necessary organic compounds, including amino acids, proteins, coenzymes, nucleic acids, and chlorophyll. Deficiency: Plants are short, leaves tend to be pale green-yellow in color, especially on the older foliage. The young leaves at the top of the plant maintain a green but paler color and tend to become smaller in size. Branching is reduced in nitrogen deficient plants resulting in short, spindly plants. The yellowing in nitrogen deficiency is uniform over the entire leaf including the veins. However in some instances, an interveinal necrosis replaces the chlorosis commonly found in many plants. In some plants the underside of the leaves and/or the petioles and midribs develop traces of a reddish or purple color. In some plants this coloration can be quite bright. As the deficiency progresses, the older leaves also show more of a tendency to wilt under mild water stress and become senescent much earlier than usual. Recovery of deficient plants to applied nitrogen is immediate (days) and spectacular.

2. Phosphorous (P): Part of many important organic compounds including sugar phosphates, ATP, nucleic acids, phospholipids, and certain coenzymes. Deficiency: Symptoms occur on the older leaves first and plant maturity is often delayed. Phosphorous deficiency in some plant species can be due to conditions being too cold for uptake of this element, rather than as lack of phosphorous in the nutrient solution. A major visual symptom is that the plants are dwarfed or stunted. Phosphorus deficient plants develop very slowly in relation to other plants growing under similar environmental conditions but without phosphorus deficiency. Phosphorus deficient plants are often mistaken for unstressed but much younger plants. Some species such as tomato, lettuce, corn and the brassicas develop a distinct purpling of the stem, petiole and the under sides of the leaves. Under severe deficiency conditions there is also a tendency for leaves to develop a blue-gray luster. In older leaves under very severe deficiency conditions a brown netted veining of the leaves may develop.

3. Potassium (K): Acts as a coenzyme or activator for many enzymes (e.g., pyruvate kinase). Protein synthesis requires high potassium levels. Plays a vital role in the regulation of stomata regarding gas exchange via osmosis. Potassium does not form a stable structural part of any molecules inside plant cells. Deficiency: The onset of potassium deficiency is generally characterized by a marginal chlorosis progressing into a dry leathery tan scorch on recently matured leaves. This is followed by increasing interveinal scorching and/or necrosis progressing from the leaf edge to the midrib as the stress increases. As the deficiency progresses, most of the interveinal area becomes necrotic, the veins remain green and the leaves tend to curl and crinkle. In contrast to nitrogen deficiency, chlorosis is irreversible in potassium deficiency, even if potassium is given to the plants. Because potassium is very mobile within the plant, symptoms only develop on young leaves in the case of extreme deficiency.

4. Sulfur (S): Incorporated into several organic compounds including amino acids (cystine, cysteine, glutathione and methionine) and corresponding proteins. Coenzyme A and the vitamins thiamine and biotin also contain sulfur. Sulfur is present in glycosides, which give the characteristic odors and flavors to mustard, onion and garlic plants. Deficiency: The visual symptoms of sulfur deficiency are very similar to the chlorosis found in nitrogen deficiency. However, in sulfur deficiency the yellowing is much more uniform over the entire plant including young leaves. The reddish color often found on the underside of the leaves and the petioles has a more pinkish tone and is much less vivid than that found in nitrogen deficiency. With advanced sulfur deficiency brown lesions and/or necrotic spots often develop along the petiole, and the leaves tend to become more erect and often twisted and brittle.

5. Magnesium (M): An essential part of the chlorophyll molecule and required for activation of many enzymes including steps involving ATP bond breakage. Essential to maintain ribosome structure. Deficiency: In its advanced form, magnesium deficiency may superficially resemble potassium deficiency. In the case of magnesium deficiency the symptoms generally start with mottled chlorotic Chlorosis : A condition in plants resulting from the failure of chlorophyll to develop caused by a deficiency of an essential nutrient. Leaves of chlorotic plants range from light green through yellow to almost white. Chlorosis may be a symptom of a number of different plant ailments, including mineral deficiencies (commonly, iron) and some diseases. It occurs as a result of reduced chlorophyll production, turning newer (usually) growth yellow. In established leaves, areas between the veins yellow first. areas developing in the interveinal tissue. The interveinal laminae tissue tends to expand proportionately more than the other leaf tissues, producing a raised puckered surface, with the top of the puckers progressively going from chlorotic to necrotic Necrotic : From Greek nekrosis; localized death of living tissue. tissue. Deficiency is common on tomato crops with the older leaves developing yellowed areas between the veins, which stay green.

6. Calcium (Ca): Often precipitates as crystals of calcium oxalate in vacuoles. Found in cell walls as calcium pectate, which cements together primary walls of adjacent cells. Required to maintain membrane integrity and is part of the enzyme amylase. Sometimes interferes with the ability of magnesium to activate enzymes. Deficiency: The very low mobility of calcium is a major factor determining the expression of calcium deficiency symptoms in plants. Classic symptoms of calcium deficiency include blossom-end rot of tomato (burning of the end part of tomato fruits), tip burn of lettuce, blackheart of celery and death of the growing regions in many plants. All these symptoms show soft dead necrotic tissue at rapidly growing areas, which is generally related to poor translocation of calcium to the tissue rather than a low external supply of calcium. Very slow growing plants with a deficient supply of calcium may re-translocate sufficient calcium from older leaves to maintain growth with only a marginal chlorosis of the leaves. This ultimately results in the margins of the leaves growing more slowly than the rest of the leaf, causing the leaf to cup downward. This symptom often progresses to the point where the petioles develop but the leaves do not, leaving only a dark bit of necrotic tissue at the top of each petiole. Plants under chronic calcium deficiency have a much greater tendency to wilt than non-stressed plants.

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From the air and water
7. Carbon (C): Constituent of all organic compounds found in plants. Sole source of C is CO2.
Deficiency: Deficiency comes from lack of airflow. Without a reliable way to bring fresh air into a grow room (generator, CO2 tank, exhaust fan, etc.) Co2 will become a deficiency and photosynthesis will stop.

8. Hydrogen (H): Constituent of all organic compounds of which carbon is a constituent. Important in cation exchange in plant-nutrient relations.

9. Oxygen (O): Constituent of many organic compounds in plants. Only a few organic compounds, such as carotene, do not contain oxygen. Also involved in anion exchange between roots and the external medium. It is terminal acceptor of H+ in aerobic respiration.

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Micronutrients

10. Iron (Fe): Required for chlorophyll synthesis and is an essential part of the cytochromes, which act as electron carriers in photosynthesis and respiration. Is an essential part of ferredoxin and possibly nitrate reductase. Activates certain other enzymes. Deficiency: The most common symptom for iron deficiency starts out as an interveinal chlorosis of the youngest leaves, evolves into an overall chlorosis, and ends as a totally bleached leaf. The bleached areas often develop necrotic spots. Up until the time the leaves become almost completely white they will recover upon application of iron. In the recovery phase the veins are the first to recover as indicated by their bright green color. This distinct venial re-greening observed during iron recovery is probably the most recognizable symptom in all of classical plant nutrition. Because iron has a low mobility, iron deficiency symptoms appear first on the youngest leaves. Deficiency shows as a distinct yellowing between the leaf veins, which stay green, on the new growth and younger leaves (this distinguishes it from magnesium deficiency which shows first on the older leaves). On crops such as tomatoes, iron deficiency may show when conditions are to cold for uptake, rather than be caused by an actual deficiency in solution.

11. Chlorine (Cl): Required for photosynthesis where it acts as an enzyme activator during the production of oxygen from water. Additional functions are suggested by effects of deficiency on roots. Deficiency: Plants require relatively high chlorine concentration in their tissues. Chlorine is very abundant in soils, and reaches high concentrations in saline areas, but it can be deficient in highly leached inland areas. The most common symptoms of chlorine deficiency are chlorosis and wilting of the young leaves. The chlorosis occurs on smooth flat depressions in the interveinal area of the leaf blade. In more advanced cases there often appears a characteristic bronzing on the upper side of the mature leaves. Plants are generally tolerant of chloride, but some species such as avocados, stone fruits, and grapevines are sensitive to chlorine and can show toxicity even at low chloride concentrations in the soil. Roots become stunted and thickened near tips.

12. Manganese (Mn): Activates one or more enzymes in fatty-acid synthesis, the enzymes responsible for DNA and RNA formation, and the enzyme isocitrate dehydrogenase in the Krebs cycle. Participates directly in the photosynthetic production of oxygen from water and may be involved in chlorophyll formation. Deficiency: The early stages of the chlorosis induced by manganese deficiency are somewhat similar to iron deficiency. They begin with a light chlorosis of the young leaves and netted veins of the mature leaves especially when they are viewed through transmitted light. As the stress increases, the leaves take on a gray metallic sheen and develop dark freckled and necrotic areas along the veins. A purplish luster may also develop on the upper surface of the leaves.

13. Boron (B): Role in plants not well understood. May be required for carbohydrate transport in phloem. Deficiency: The early stages of the chlorosis induced by manganese deficiency are somewhat similar to iron deficiency. They begin with a light chlorosis of the young leaves and netted veins of the mature leaves especially when they are viewed through transmitted light. As the stress increases, the leaves take on a gray metallic sheen and develop dark freckled and necrotic areas along the veins. A purplish luster may also develop on the upper surface of the leaves. In plants with poor boron mobility, boron deficiency results in necrosis of meristematic tissues in the growing region, leading to loss of apical dominance and the development of a rosette condition. These deficiency symptoms are similar to those caused by calcium deficiency. In plants in which boron is readily transported in the phloem, the deficiency symptoms localize in the mature tissues, similar to those of nitrogen and potassium. Both the pith and the epidermis of stems may be affected, often resulting in hollow or roughened stems along with necrotic spots on the fruit. The leaf blades develop a pronounced crinkling and there is a darkening and crackling of the petioles often with exudation of syrupy material from the leaf blade. The leaves are unusually brittle and tend to break easily. Also, there is often a wilting of the younger leaves even under an adequate water supply, pointing to a disruption of water transport caused by boron deficiency.

14. Zinc (Zn): Required for the formation of the hormone indoleacetic acid. Activates the enzymes alcohol dehydrogenase, lactic acid dehydrogenase, glutamic acid dehydrogenase and carboxypeptidase. Deficiency: In the early stages of zinc deficiency the younger leaves become yellow and pitting develops in the interveinal upper surfaces of the mature leaves. As the deficiency progress these symptoms develop into an intense interveinal necrosis but the main veins remain green, as in the symptoms of recovering iron deficiency. In many plants, especially trees, the leaves become very small and the internodes shorten, producing a rosette like appearance.

15. Copper (Cu): Acts as an electron carrier and as part of certain enzymes. Part of plastocyanin which is involved in photosynthesis, and also of polyphenol oxidase and possible nitrate reductase. May be involoved in nitrogen fixing. Deficiency: Copper deficiency may be expressed as a light overall chlorosis along with the permanent loss of turgor in the young leaves. Recently matured leaves show netted, green veining with areas bleaching to a whitish gray. Deficiency is rare, but young leaves may become dark green and twisted or misshapen, often with brown dry spots.

16. Molybdenum (Mo): Acts as an electron carrier in conversion of nitrate to ammonium and is also essential for nitrogen fixation. Deficiency: An early symptom for molybdenum deficiency is a general overall chlorosis, similar to the symptom for nitrogen deficiency but generally without the reddish coloration on the undersides of the leaves. This results from the requirement for molybdenum in the reduction of nitrate, which needs to be reduced prior to its assimilation by the plant. Thus, the initial symptoms of molybdenum deficiency are in fact those of nitrogen deficiency. However, molybdenum has other metabolic functions within the plant, and hence there are deficiency symptoms even when reduced nitrogen is available. In many plants there is an upward cupping of the leaves and mottled spots developing into large interveinal chlorotic areas under severe deficiency. At high concentrations, molybdenum has a very distinctive toxicity symptom in that the leaves turn a very brilliant orange.

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Others
Although most higher plants require those 16 essential elements, certain species may need others. They may, at least, accumulate these other elements even if they are not essential to their normal growth.

17. Cobalt : One of eight micronutrients essential to plant health. Cobalt is thought to be an important catalyst in nitrogen fixation. It may need to be added to some soils before seeding legumes

18. Silicon (Si): Silicon is believed to be used for support. It adds strength to tissues, giving resistence to fungal infection.

19. Nickel (Ni): Nickel is believed by some to be an essential element. It is used in production of the urease enzyme.

20. Sodium (Na): Sodium stimulates the growth of certain plants such as beets and turnips under some conditions. However, it is not considered essential since plants can complete their growth cycle in its absence.

For additional deficiency pics and info: http://www.ipmimages.org/browse/subimages.cfm?sub=766

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Carbohydrates

A carbohydrate is an organic compound produced by photosynthesis that is composed of atoms of carbon, hydrogen and oxygen in a ratio of 1: 2:1, respectively. Some carbohydrates are relatively small molecules; the most important is glucose, which has 6 carbon atoms and is the end product of photosythesis. If carbon dioxide, water, and appropriate minerals are available, plants, with the aid of solar energy, can synthesize all the different carbohydrates, proteins, and lipids they need for their existence. Plants are relatively unique in this ability, as most organisms cannot do this. It follows that life on Earth ultimately depends on the process of carbon dioxide assimilation and oxygen production via photosynthesis and its corresponding energy production in which carbohydrates are the first intermediates. The utilization of carbohydrate via oxidation occurs in a reaction that is the reverse of photosynthesis. In plants the glucose is stored as starch and sucrose. Carbohydrate metabolic processes are subject to regulatory controls in which various hormones play a predominant role. Carbohydrates are very important to plant processes. They are the driving energy force of plants. After producing carbohydrates, a plant uses them as energy, stores them, or builds them into complex energy compounds such as oils and proteins. All of these food products are called photosynthates. The plant uses them when light is limited, or transports them to its roots or

Carbon dioxide + Water + Sunlight = Sugar + Oxygen
or
6 CO2 + 6 H20 + Energy => C6H1206 + 6 02

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Proteins
Proteins are a primary constituent of living things and are involved in practically every function performed by a cell, including regulation of cellular functions such as signal transduction and metabolism. They are formed of long chains of amino acids that are specific depending on the job at hand. Regions of DNA that encode proteins are first transcribed into messenger RNA and then translated into protein using amino acids as building blocks and enzymes as catalysts. By examining the DNA sequence alone we can determine the sequence of amino acids that will appear in the final protein. This is the mechanism for DNA sequencing and articulation used in cloning of higher animals. Various molecules and ions are able to bind to specific sites on proteins. These sites are called binding sites. They exhibit chemical specificity. The particle that binds is called a ligand. The strength of ligand-protein binding is a property of the binding site known as affinity. Proteins differ from carbohydrates chiefly in that they contain much nitrogen and a little bit of sulfur, besides carbon, oxygen, and hydrogen.

Proteins are polypeptides, long or short strands of amino acids usually between 10-100 long bonded by peptide bonds. The sequence of covalently linked amino acids is known as the primary structure of a protein.

The secondary structures of proteins involve segments of polypeptides folded locally into stable structures that include -helices and -pleated sheets (i.e. the R groups in the above photo). The secondary structure of a protein is vital in determining and allowing its respective role in the plant.

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Amino Acids
Amino Acids are the building blocks and fundamental ingredient in the process of protein synthesis. Proteins are formed by a sequence of amino acids. Plants synthesize amino acids from primary elements. They can also be delivered via various products discussed below. The carbon, oxygen, and hydrogen obtained from the air, form carbon hydrate by means of photosynthesis, which combines with nitrogen obtained from nutrients in the soil or fertilizer solution, leading to synthesis of amino acids by collateral metabolic pathways. Amino acids have a chelating effect on micronutrients as well as a beneficial effect on cell permeability, amongst various other functions. When applied together with micronutrients, the absorption and transportation of micronutrients inside the plant is facilitated. Glycine and Glutamic Acid are fundamental metabolites in the process of formation of vegetable tissue and chlorophyll synthesis. These amino acids help to increase chlorophyll concentration in the plant leading to higher degree of photosynthesis and, in turn, higher yields.

The requirement of amino acids in essential quantities is well known as a means to increase yield and overall quality of crops. This is especially important when growing with hydroponics. Many organic fertilizers contain these materials already, but refined mineral hydroponic fertilizers more than likely do not. This is an advantage to the hydroponic grower, in that they can maintain an element of sanitation and control over the growing process, but also means the grower must be aware that there are materials plants can use to optimize growth over and above a simple NPK fertilizer. In other words, the advantage of being able to specify your growing cocktail needs to be augmented with the knowledge of what plants need and what materials can be used. Experiment, the proof is in the pudding. Know what your plants desire, read your labels, and give them exactly that!

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Enzymes

Enzymes are biological catalysts. Most, if not all, plant metabolic processes are enzyme driven. Plants use energy via active transport and other processes to move water and nutrient through cells up to the leaves where, through the process of photosynthesis, these elements are converted to sugars and starches which are, in turn, sent back down to the root zone for potential storage. Plants must produce the enzymes necessary to take up these nutrients, minerals, and vitamins. This process also requires energy (sugars and starches); now consider how much extra energy your plants could use for fruit or flower production if we supplied a good portion of these enzymes?

Enzymes also play other important roles in plant growth. For example, every hydroponic gardener has probably experienced the dreaded destruction that root disease can wreak upon a garden. Why aren't all the plants that live outside dying of Pythium infection? Simply put, Mother Nature takes care to balance this relationship by creating naturally occurring enzymes via beneficial microbes that keep the root zone in balance and free of this crippling plant sickness. In a hydroponic scenario there is no such given balance. Dead and decaying root matter is the substrate upon which Pythium will grow, that is why whenever we have root disease in a hydroponic system we see that our roots are soft to the touch, brown or black, mucousy, and usually falling apart. Enzymes are found in our mouths and stomachs and effectively help in breaking down the materials we ingest. Similarly, enzymes can dissolve decaying root matter and convert it to sugars and starches, thus pulling the carpet right out from underneath the feet of root disease. Enzymes are one of the components of dynamic plant growth occurring readily in nature that we can utilize in our hydroponic or container gardens effectively.

Enzyme formulations that are capable of ensuring dynamic root growth and the ensured absence of root diseases in hydroponic and soil situations, in addition to having a positive benefit on your growth. Enzymes are also effective in breaking up and conditioning clay or hardpan soils.

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Vitamins
Think of plant vitamins the same way you would human vitamins. In fact, there is almost universal overlap in the vitamins they, and all organisms, use. While there are myriad vitamins involved in natural processes, these are some that have the most benefit to plant growth. Vitamins are to be thought of as cofactors for enzymes involved in carbohydrate metabolism and the biosynthesis of macromolecules.

Thiamine (Vitamin B1)

A colorless compound with chemical formula C12H17ClN4OS. B1 is produced in the foliage of plants and transported down to the root system where it has an effect on root growth and development. In tissue culture and rooting preparations, B1 helps to stimulate the growth of roots on new

Riboflavin (B2) Green plants and most microorganisms can synthesize it; animals need to acquire it in their diet. It exists in combined forms as coenzymes and functions in the metabolism of carbohydrates and amino acids.

Pyridoxine (B6) Pyridoxal phosphate functions as a cofactor in enzymes involved in reactions required for the synthesis and catabolism of amino acids.

Ascorbic acid (Vit C) Ascorbic acid may be found in all the compartments in the plant cell, where it plays diverse roles. It is known to be involved in cell division and cell wall synthesis and also acts as an inhibitor of dangerous compounds such as hydrogen peroxide and the dangerous radicals of oxygen generated as a by-product of respiratory and photosynthetic machinery of the cell. Other plant functions of Vitamin C are as an enzyme activator, a promoter of stem growth, and it is required for production of certain proteins used in cell walls.

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Hormones
A hormone is a signal that controls the growth and development of a plant. The same way hormones regulate facial hair growth in male puberty and height growth during adolescents in humans, hormones in plants regulate rooting, vegetative growth, and flowering. They are produced naturally by plants, while plant growth regulators (PGR) are synthetically produced substances applied to plants to influence growth and development in a way similar to hormones. All plant hormones and PGR's are in fact 'organic' in that they contain carbon and nitrogen, however these can be divided into either synthetic (man made) compounds (such as IBA used in rooting powders/gels, or cycocel) that mimic naturally occurring plant hormones, or they can be naturally occurring substances that have been extracted from plant tissues.

The five major plant hormones can be divvied into three basic categories- growth hormones, stress hormones and shock hormones. Auxins and cytokenins are considered growth hormones, Ethylene and Gibberillens are considered stress hormones, and abscisic acid is considered a shock hormone. All three types of hormones are similar in that they fall within the classic definition of an intercellular hormone. They are made by a cell and are meant to affect the behavior of other cells, either in nearby tissue or at the opposite end of the plant.

Plant hormone products are not vital to success in plant cultivation, but after the basics are understood it is highly beneficial to implement some sort of hormone schedule into your grow cocktail. You will see a visible and positive result, guaranteed. It is said that a plant in the outside environment produces only 10% of the hormone that it can synthesize. A hormone is a signal. Higher levels of the signal, higher levels of what it's signaling for. By supplying the other 90% significant increases in yields can be experienced.

Auxins

The term auxin is derived from the Greek word 'auxein' which means to grow. Compounds are generally considered auxins if they can be characterized by their ability to induce cell elongation in stems and otherwise resemble indoleacetic acid (the first auxin isolated) in physiological activity. Auxins usually affect other processes in addition to cell elongation of stem cells, but this characteristic is considered critical of all auxins and thus helps define the hormone. Auxins were the first plant hormones discovered. Charles Darwin was among the first scientists to dabble in plant hormone research. In his book "The Power of Movement in Plants"

Functions of Auxin

• Stimulates cell elongation
• Stimulates differentiation of phloem and xylem
• Stimulates root initiation on stem cuttings and lateral root development in tissue culture
• Mediates the tropistic response of bending in response to gravity and light
• The auxin supply from the apical bud suppresses growth of lateral buds
• Delays leaf senescence
• Can induce fruit setting and growth in some plants
• Stimulates growth of flower parts
• Promotes (via ethylene production) femaleness in dioecious flowers
• Stimulates the production of ethylene at high concentrations

Gibberellins (GA)

GA's are widespread and so far ubiquitous in both angiosperms and gymnosperms, as well as ferns. There have been 126 GA's isolated, all of which are most likely not essential to the plant. Instead, these forms are probably inactive precursors or breakdown products of active gibberellins. Unlike the classification of auxins, which are classified on the basis of function, gibberellins are classified on the basis of structure as well as function. All gibberellins are derived from the ent-gibberellane skeleton shown above. Gibberellins promote stem elongation. They are not produced in the stem tip like auxins. Synthetic compounds such as Cycocel have been produced which are 'anti-gibberellins' and force a plant to remain dwarfed by blocking the elongation effect of the plants natural Gibberillins.

Functions of Gibberellins

• Stimulate stem elongation by stimulating cell division and elongation.
• Breaks seed dormancy in some plants, which require stratification or light to induce germination.
• Can cause parthenocarpic (seedless) fruit development.
• Can delay senescence in leaves and citrus fruits.

Cytokinins

Cytokinins are compounds with a structure resembling adenine, which promotes cell division, and have other similar functions to kinetin. Kinetin was the first cytokinin discovered and so named because of the compounds ability to promote cytokinesis (cell division). Though it is a natural compound, it is not made in plants, and is therefore usually considered a "synthetic" cytokinin (meaning that the hormone is synthesized somewhere other than in a plant). The most common form of naturally occurring cytokinin in plants today is called zeatin, which was isolated from corn (Zea mays). Cytokinins have been found in almost all higher plants as well as mosses, fungi, bacteria, and also in tRNA of many prokaryotes and eukaryotes. Today

Cytokinin Functions

• Stimulates cell division.
• Stimulates morphogenesis (shoot initiation/bud formation) in tissue culture.
• Stimulates the growth of lateral buds-release of apical dominance.
• Stimulates leaf expansion resulting from cell enlargement.
• May enhance stomatal opening in some species.

Abscisic Acid (ABA)

ABA is a naturally occurring compound in plants. It is a single compound unlike the auxins, gibberellins, and cytokinins. It was called "abscisin II" originally because it was thought to play a major role in abscission of fruits. At about the same time another group was calling it "dormin" because they thought it had a major role in bud dormancy. The name abscisic acid (ABA) was coined by a compromise between the two groups. Though ABA generally is thought to play mostly inhibitory roles, it has many promoting functions as well.

Functions of Abscisic Acid

• Stimulates the closure of stomata (water stress brings about an increase in ABA synthesis).
• Induces seeds to synthesize storage proteins.
• Has some effect on induction and maintenance of dormancy.
• Induces gene transcription especially for proteinase inhibitors in response to wounding which may explain an apparent role in pathogen defense.

Functions of Ethylene

• Stimulates the release of dormancy.
• Stimulates shoot and root growth and differentiation (triple response)
• May have a role in adventitious root formation.
• Induction of femaleness in dioecious flowers.
• Stimulates flower opening.
• Stimulates flower and leaf senescence.
• Stimulates fruit ripening.

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Chelates and Humic Acids
The word chelate (pronounced: "key-late") comes from the Greek word "chele" which literally means "claw". Researchers first used the word chelate in the 1920s because it describes the principal of grasping and holding something, which is essentially what occurs in the process of chelation. Specifically, a chelate is a chemical compound in the form of a heterocyclic ring, containing a metal ion attached by coordinate bonds to at least two nonmetal ions. Generally, think of a chelate as a receptor or binding site for micronutrients that maintains their availability to the plant by forming a bridge between the nutrient and the root zone. Micronutrients are crucial partners in every metabolic function of the plant. Respiration, photosynthesis, protein synthesis, energy transfer, cell division, and cell elongation are all dependent on an adequate supply of calcium, iron, copper, manganese, zinc, and other micronutrients.

Synthetic
There are synthetic and organic forms of chelates. Read the label of your hydroponic fertilizer and there should be "EDTA" beside some of the trace elements. If you also see "DTPA" you are using a more complex fertilizer. If you see "EDDHA" beside iron, you are using a very high quality fertilizer.

Ethylenediaminetetraacetate (EDTA) is the most common chelating agent found in synthetic fertilizers. Like other synthetic chelates, EDTA is an alien compound to the plant and is therefore not absorbed by the plant. When the chelated element is required, the plant will remove the element, for example iron, from the chelate and absorb the element. However, since the chelating agent is foreign to the plant, it will give up the chelating agent (EDTA) back into solution where it is free to chelate other positively charged elements. EDTA is better suited to slightly lower than neutral pH levels. Iron often becomes deficient at higher pH values such as those typically associated with uncalibrated rockwool or mineral soils. EDTA has four points of connection to the element it chelates. In some situations four points of connection mayhold the element

Diethylenetriaminepentaacetate (DTPA) is a chelating agent better suited to high pH levels. As the chemical name suggests, it has five (penta) points of connection to the element it chelates. DTPA is more costly than EDTA and is less soluble so it is found in smaller quantities than EDTA in most synthetic fertilizer formulations.

Studies suggest that ethylenediam