Hydroponic Nutrients Explained
Nutrients are the basis of any hydroponic system and since we need to meet all of the plants nutritional requirements, it's important to know what you are supplying and what can go wrong.
With any nutrient solution, the two factors to keep in mind are firstly the composition of your nutrient - does it contain all of the elements required for plant growth in the correct ratios. And secondly, with your balanced and complete nutrient solution, what strength or EC should it be running at for your particular crop, stage of growth and type of hydroponic system, and how do we measure this.
The Nutrient Solution - Composition
Many growers prefer to buy a pre-mixed nutrient solution which simply needs to be diluted (for liquid concentrates) or dissolved in water before use. Often these pre-made nutrients come in two, three, four or even more parts so a grower can change the ratio of the mineral elements to allow for either vegetative or fruiting growth or for different crops.
There are many excellent brands of these pre-mixed nutrients on the market, however, many growers have come across major problems when they try to use some of the indoor plant food or other nutrients which have been designed for plants growing in soil or a pre fertilized potting mix.
Often these types of products are not suitable for hydroponics because they are not designed to be a complete plant food. It is always preferable to buy a nutrient mix which is sold especially for hydroponic use, and is a complete plant food. To be complete a hydroponic nutrient needs to have the essential elements for plant growth these are:
- Primary Macro-Nutrients:
- Nitrogen (N)
- Potassium (K)
- Phosphorus (P)
- Secondary Macro-Nutrients:
- Calcium (Ca)
- Magnesium (Mg)
- Sulfur (S)
- Iron (Fe)
- Manganese (Mn)
- Copper (Cu)
- Zinc (Zn)
- Molybdenum (Mo)
- Boron (B)
- Chlorine (Cl)
- Silicon (Si)
The essential macro nutrients used in hydroponic nutrient solutions are typically calcium nitrate, potassium sulphate, potassium nitrate, mono potassium phosphate, and magnesium sulphate. Each element involved in these nutrients provides a different benefits to a plants health.
- Hydrogen forms water by combining with the oxygen.
- Nitrogen and sulfur are essential to the supply of amino acids and proteins.
- Phosphorus is used in photosynthesis and overall growth.
- Potassium and magnesium act as catalysts in the creation of starches and sugars.
- Magnesium and nitrogen also play a role in the production of chlorophyll.
- Calcium is a part of the make-up of cell walls, and plays a role in the growth of cells.
The levels that these elements are present in your hydroponic nutrient tend to vary between brands, since there is no one single recommendation for concentrations. Many nutrients may also contain some of the beneficial elements such as Nickel (Ni),Cobalt (Co), Silica (Si) or Selenium (Se). While these are not essential (plants will still grow without them), they can be beneficial to many crops.
Whether you make your own nutrient solution from the different fertilizer salts, or buy a pre-made brand, problems can, an often do, arise with deficiencies of one of more of the nutrient elements. Common reasons for this are that
- The nutrient strength may be too low, resulting in insufficient nutrients for the plants in general.
- The nutrient formula you are using may not be completely balanced, and one (or more of the elements) may be deficient.
- Occasionally, growers may unintentionally leave out one of the fertilizer salts or the wrong fertilizer was used when the nutrient formula was weighted out.
And just to complicate matters further, even if your solution is well balanced, sometimes environmental and internal plant conditions prevent the uptake of certain nutrients and deficiency symptoms then result.
Signs of Nutrient Deficiency
Each of the mineral elements required by the plant has its own set of deficiency signs and symptoms and growers can learn to identify many of these. Many of the signs are similar in appearance, but others are very distinct and most good gardening and hydroponic books will detail what these signs are. Briefly, the deficiency symptoms for each of the elements are listed below (these may vary slightly between different plant species and depending on how severe the deficiency is.
Nutrient Deficiency Symptoms
Boron biochemical functions are yet uncertain, but evidence suggests it is involved in the synthesis of one of the bases for nucleic acid (RNA uracil) formation. It may also be involved in some cellular activities such as division, differentiation, maturation and respiration. It is associated with pollen germination.
Boron Deficiency: Plants deficient in boron exhibit brittle abnormal growth at shoot tips and one of the earliest symptoms is failure of root tips to elongate normally. Stem and root apical meristems often die. Root tips often become swollen and discolored. Internal tissues may rot and become host to fungal disease. Leaves show various symptoms which include drying, thickening, distorting, wilting, and chlorotic or necrotic spotting.
Boron Toxicity: Yellowing of leaf tip followed by necrosis of the leaves beginning at tips or margins and progressing inward before leaves die and prematurely fall off. Some plants are especially sensitive to boron accumulation.
Despite being a secondary nutrient, calcium is essential for plants to develop properly. It plays a key role in cell-walls, stems, petioles and branches. It is also needed for root growth, especially the tips of the roots. Sometimes it is used to buffer an excess of other elements and balance the amount of nutrients. Calcium plays an important role in maintaining cell integrity and membrane permeability.
Calcium Deficiency: Young leaves are affected first and become small and distorted or chlorotic with irregular margins, spotting or necrotic areas. Bud development is inhibited, blossom end rot and internal decay may also occur and root may be under developed or die back. Deficiency will cause leaf tip die-back, leaf tip curl and marginal necrosis and chlorosis primarily in younger leaves. Symptoms: young leaves develop chlorosis and distortion such as crinkling, dwarfing, developing a strap-like shape, shoots stop growing and thicken.
Calcium Toxicity: Difficult to distinguish visually. May precipitate with sulfur in solution and cause clouding or residue in tank. Excess calcium may produce deficiencies in magnesium and potassium.
Chlorine is involved in the evolution of oxygen in the photosynthesis process and is essential for cell division in roots and leaves. Chlorine raises the cell osmotic pressure and affects stomata regulation and increases the hydration of plant tissue. Levels less than 140 ppm are safe for most plants. Chloride sensitive plants may experience tip or marginal leaf burn at concentrations above 20 ppm.
Chlorine Deficiency: Wilted chlorotic leaves become bronze in color. Roots become stunted and thickened near tips. Plants with chlorine deficiencies will be pale and suffer wilting.
Chlorine Toxicity: Burning of leaf tip or margins. Bronzing, yellowing and leaf splitting. Reduced leaf size and lower growth rate.
Copper is a constituent of many enzymes and proteins. Assists in carbohydrate metabolism, nitrogen fixation and in the process of oxygen reduction.
Copper Deficiency: Symptoms of deficiency are a reduced or stunted growth with a distortion of the younger leaves and growth tip die-back. Young leaves often become dark green and twisted. They may die back or just exhibit necrotic spots. Growth and yield will be deficient as well.
Copper Toxicity: Copper is required in very small amounts and readily becomes toxic in solution culture if not carefully controlled. Excess values will induce iron deficiency. Root growth will be suppressed followed by symptoms of iron chlorosis, stunting, reduced branching, abnormal darkening and thickening of roots.
Iron is an important component of plant enzyme systems for electron transport to carry electrons during photosynthesis and terminal respiration. It is a catalyst for chlorophyll production and is required for nitrate and sulfate reduction and assimilation.
Iron deficiency: Pronounced interveinal chlorosis similar to that caused by magnesium deficiency but on the younger leaves. Leaves exhibit chlorosis (yellowing) of the leaves mainly between the veins, starting with the lower and middle leaves.
Caused by factors that interfere with iron absorption of roots: over irrigation, excessive soluble salts, inadequate drainage, pests, high substrate pH, or nematodes. This is easily corrected by adding an iron supplement with the next watering.
Iron Toxicity: Excess accumulation is rare but could cause bronzing or tiny brown spots on leaf surface.
Manganese is involved in the oxidation reduction process in the photosynthetic electron transport system. Biochemical research shows that this element plays a structural role in the chloroplast membrane system, and also activates numerous enzymes.
Manganese Deficiency: Interveinal chlorosis of younger leaves, necrotic lesions and leaf shredding are typical symptom of this deficiency. High levels can cause uneven distribution of chlorophyll resulting in blotchy appearance. Restricted growth and failure to mature normally can also result.
Manganese Toxicity: Toxicity:Chlorosis, or blotchy leaf tissue due to insufficient chlorophyll synthesis. Growth rate will slow and vigor will decline.
Magnesium is a component of the chlorophyll molecule and serves as a cofactor in most enzymes.
Magnesium deficiency: Magnesium deficiency will exhibit a yellowing (which may turn brown) and interveinal chlorosis beginning in the older leaves. The older leaves will be the first to develop interveinal chlorosis. Starting at leaf margin or tip and progressing inward between the veins.
Magnesium Toxicity: Magnesium toxicity is rare and not generally exhibited visibly. Extreme high levels will antagonize other ions in the nutrient solution.
Molybdenum is a component of two major enzyme systems involved in the nitrate reeducates, this is the process of conversion of nitrate to ammonium.
Molybdenum Deficiencies: Often interveinal chlorosis which occurs first on older leaves, then progressing to the entire plant. Developing severely twisted younger leaves which eventually die. Molybdenum deficiencies frequently resemble nitrogen, with older leaves chlorotic with rolled margins and stunted growth.
Molybdenum Toxicity: Excess may cause discoloration of leaves depending on plant species. This condition is rare but could occur from accumulation by continuous application. Used by the plant in very small quantities
Nitrate - Ammonium is found in both inorganic and organic forms in the plant, and combines with carbon, hydrogen, oxygen and sometimes sulfur to form amino acids, amino enzymes, nucleic acids, chlorophyll, alkaloids, and purine bases. Nitrogen rates high as molecular weight proteins in plant tissue.
Plants need lots of Nitrogen during vegging, but it's easy to overdo it. Added too much? Flush the soil with plain water. Soluble nitrogen (especially nitrate) is the form that's the most quickly available to the roots, while insoluble N (like urea) first needs to be broken down by microbes in the soil before the roots can absorb it. Avoid excessive ammonium nitrogen, which can interfere with other nutrients.
Nitrogen Deficiencies: Plants will exhibit lack of vigor, slow growth and will be weak and stunted. Quality and yield will be significantly reduced. Older leaves become yellow (chlorotic) from lack of chlorophyll. Deficient plants will exhibit uniform light green to yellow on older leaves, these leaves may die and drop. Leaf margins will not curled up noticeably. Chlorosis will eventually spread throughout the plant. Stems, petioles and lower leaf surfaces may turn purple.
Nitrogen Toxicity: Leaves are often dark green and in the early stages abundant with foliage. If excess is severe, leaves will dry and begin to fall off. Root system will remain under developed or deteriorate after time. Fruit and flower set will be inhibited or deformed.
Phosphorus is a component of certain enzymes and proteins, adenosine triphosphate (ATP), ribonucleic acids (RNA), deoxyribonucleic acids (DNA) and phytin. ATP is involved in various energy transfer reactions, and RNA and DNA are components of genetic information.
Phosphorus deficiency: Figure 11 is severe phosphorus (P) deficiency during flowering. Fan leaves are dark green or red/purple, and may turn yellow. Leaves may curl under, go brown and die. Small-formed buds are another main symptom. Phosphorus deficiencies exhibit slow growing, weak and stunted plants with dark green or purple pigmentation in older leaves and stems.
Phosphorus Toxicity: This condition is rare and usually buffered by pH limitations. Excess phosphorus can interfere with the availability and stability of copper and zinc.
Potassium is involved in maintaining the water status of the plant and the tugor pressure of it's cells and the opening and closing of the stomata. Potassium is required in the accumulation and translocation of carbohydrates. Lack of potassium will reduce yield and quality.
Potassium deficiency: Older leaves are initially chlorotic but soon develop dark necrotic lesions (dead tissue). First apparent on the tips and margins of the leaves. Stem and branches may become weak and easily broken, the plant may also stretch. The plant will become susceptible to disease and toxicity. In addition to appearing to look like iron deficiency, the tips of the leaves curl and the edges burn and die.
Potassium Toxicity: Usually not absorbed excessively by plants. Excess potassium can aggravate the uptake of magnesium, manganese, zinc and iron and effect the availability of calcium.
Sulfate is involved in protein synthesis and is part of the amino acids, cystine and thiamine, which are the building blocks of proteins. It is active in the structure and metabolism in the plant. It is essential for respiration and the synthesis and breakdown of fatty acids.
Sulphur deficiency: The initial symptoms are the yellowing of the entire leaf including veins usually starting with the younger leaves. Leaf tips may yellow and curl downward. Sulfur deficiencies are light green fruit or younger leaves with a lack of succulence. Elongated roots and woody stem. Although many varieties of cannabis do get purplish stems, the trait generally extends the entire length of the plant's stem, and not just near the top as in this specimen.
Sulphur Toxicity: Leaf size will be reduced and overall growth will be stunted. Leaves yellowing or scorched at edges. Excess may cause early senescence.
Zinc plays a roll in the same enzyme functions as manganese and magnesium. More than eighty enzymes contain tightly bound zinc essential for their function. Zinc participates in chlorophyll formation and helps prevent chlorophyll destruction. Carbonic anhydrate has been found to be specifically activated by zinc.
Zinc Deficiencies: Deficiencies appear as chlorosis in the inter-veinal areas of new leaves producing a banding appearance as seen in figure 18. This may be accompany reduction of leaf size and a shortening between internodes. Leaf margins are often distorted or wrinkled. Branch terminals of fruit will die back in severe cases.
Zinc Toxicity: Excess Zinc is extremely toxic and will cause rapid death. Excess zinc interferes with iron causing chlorosis from iron deficiency. Excess will cause sensitive plants to become chlorotic.
Nutrient Strength - Measurement
Provided the nutrient you are using is complete and balanced, the concentration or strength of the solution has major effects on plant growth and development. This is why it is essential to be able to measure solution concentration, using a meaningful unit of measure. Many growers will still be working in ppm (parts per million), using TDS (Total dissolved solids) meters, however there is now an industry move to standardize the unit of solution measurement to EC (electrical conductivity) which is a more accurate and meaningful way to monitor your nutrient.
All a TDS or ppm meter actually does is to measure the EC (electrical conductivity) of the solution, then use an approximate conversion figure to convert this to PPM. The problem arises is that this conversion figure is never very accurate, as different nutrient solutions with different compositions of nutrient elements will have different PPM values, so using one conversion figure can be extremely inaccurate.
What the plants root system is actually responding to is the EC (or osmotic concentration) of the nutrient, so this is what we should measure. There are a number of different EC and CF (Conductivity Factor) meters, and the water resistant pen type meters are commonly used by growers. Depending on where in the world you are, the units expressed on your meter may be different, however it is easy to convert between the different units of EC.
The most commonly used units are either Microsiemens/cm (EC) or conductivity factor (CF) (depending on which country you are in). Other units used or often expressed in crop recommendations are: Millimhos, micromhos, or millisiemens (mS). The conversion between all of these units is:
1 millisiemen (EC) equals 1 millimhos, equals 1,000 microsiemens, equals 1,000 millimhos, equals 10 CF.
It is simply a matter of shifting the decimal place to convert between the different units.
Nutrient Strength - Under and Over Use
Running the correct EC for your particular crop and system is important. Some crops such as lettuce and other greens prefer a much lower EC than fruiting crops such as tomatoes, and each crop has its own ideal EC range for optimum growth. When the EC is being run to high for a particular plant, this will show as visible symptoms within the crop. A high EC, effectively puts the plants under water stress since the plant cells begin to lose water, back into the more concentrated nutrient solution surrounding the roots.
As a result, the first sign of nutrient overuse is plant wilting, even when supplied with sufficient nutrient solution. If the high EC conditions are not too severe, the plants will adjust to these conditions and you may see growth which is hard in appearance - often a darker green than usually, with shorter plants and smaller leaves. When the EC is being run to low, the opposite occurs - greater amounts of water are taken up, growth will be soft and floppy and often a lighter green in appearance.
Fruit will have less flavour and the quality of the whole crop - in terms of dry matter, shelf life, firmness and colour will be reduced. Since other factors affect EC also, such as water uptake from the solution, concentrating the nutrients during warm periods, or nutrient uptake, dropping the EC under a different environmental conditions it is vital that the EC is measured, monitored and adjusted on a regular basis.
By focusing on the two most important solution factors - nutrient balance and nutrient concentration, the hydroponic solution will give maximum growth and yields. When things do go wrong, being able to correctly identify a deficiency symptom before it begins to severely effect your plants is also important, so as always, closely watching what your crop is doing is a growers best line of defence against solution problems.
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