Sponsored by:

Plant Nutrition - essential minerals

Balanced nutrition is critical for the expression of disease resistance since nutrition is part of a delicately balanced interdependent system influenced by the plant's genetics and the environment. (Huber, D.M. & Jones, 2013) Currently, our investigation supports the model that cannabis requires about 20 elements to support all of its biochemical needs: these 20 elements are called essential nutrients.  Carbon, hydrogen and oxygen are the three backbone elements that are considered non-mineral elements which allow plants to undergo photosynthesis. Those three elements account for around 95% percent of the mass of the plant.  On average, the dry weight (excluding water) of a cell is 50 percent carbon. That makes 17 additional elements that play a role in growth. 

Nitrogen, potassium, phosphorus, calcium, magnesium and sulfur are considered macro-nutrients.  Calcium, magnesium and sulfur are also called secondary nutrients. These six elements are used in relatively large amounts by the plant. There are eleven other elements that are used in much smaller amounts and are called micro-nutrients, or trace elements. The micro-nutrients are iron, zinc, silicon, molybdenum, manganese, boron, copper, cobalt, sodium, chlorine and nickel. All 17 elements, both macro-nutrients and micro-nutrients, are essential for optimized plant growth.  Some of the micro-nutrients, such as cobalt, are required at such trace levels that they are normally present in residual amounts and are not included in fertilizers. Other trace minerals, like iron, are so important for plants, that many supplements and fertilizers will contain added iron

For optimal crop yield, producers need to recognize the symptoms of insufficient (deficiency) or excess nutrients (toxicity) in the soil. Crops are affected by immediate factors such as weather conditions or injury, excess fertilizer, pesticide drift or insect infestations which may appear to be nutrient deficiencies. It is critical to perform regular soil testing to determine nutrient levels and monitor changes in soil nutrient status. With historic soils data and information on current growing season conditions, producers, extension agents and crop advisers can more accurately assess what is affecting the crop.

flow chart for Mobile and Immobile Nutrients


Click on an element to learn about it's role in plant growth

Nitrogen (N) is an essential nutrient for leaf and stem development.  It is the primary building block for plant protoplasm, the translucent substance that is the living matter in cells.  Nitrogen is required for flower differentiation, speedy shoot growth, and the quality of the fruit set.

Phosphorus (P) is vital to the growth and health of plants.  It assists in converting the sun's energy and other elements, such as nitrogen, into usable food for plants.  It functions as one of the major players in the process of nutrient transport and energy transfer.

Potassium (K) is important for the manufacture of plant sugars/carbohydrates, increases the chlorophyll in leaves, regulates the opening and closing of leaf stomata and aids in disease resistance, water uptake and the ripening process.  It activates at lest sixty enzymes involved in plant growth!

Calcium (Ca) is an essential part of plant cell wall structure.  It is essential for good growth, and is known to contribute to improved disease resistance.  Calcium also improves the absorption of other nutrients

Magnesium (Mg) is an essential for many plant functions, including photosynthesis, sugar synthesis, starch translocation, and plant oil formation.  It is at the core of the chlorophyll molecule, and an essential ingredient for healthy plants.  It also aids in seed germination and in the formation of fruits and seeds.

Sulfur (S) is a structural component of plant proteins and enzymes.  It is also part of some vitamins, and helps to support many function that can affect the final yield and quality of plants.


Iron (Fe) is a constituent of several enzymes and some pigments, and assists in nitrate and sulfate reduction and energy production within the plant. Although iron is not used in the synthesis of chlorophyll (the green pigment in leaves), it is essential for its formation. This explains why plants deficient in iron show chlorosis in the new leaves.

Zinc (Zn) activates enzymes that are responsible for the synthesis of certain proteins. It is used in the formation of chlorophyll and some carbohydrates, conversion of starches to sugars and its presence in plant tissue helps the plant to withstand cold temperatures. Zinc is essential in the formation of auxins, which help with growth regulation and stem elongation.

Silicon (Si) has been found to improve drought tolerance and delay wilting in certain crops where irrigation is withheld and may enhance the plant’s ability to resist micronutrient and other metal toxicities (i.e. aluminum, copper, iron, manganese, zinc, etc.).  Also, silicon has been found to help increase stem strength.  Silicon has been found to increase certain plant species resistance to fungal pathogen attack.  The modes of action for most of these benefits are uncertain and more research needs to verify these benefits.

Molybdenum (Mo) is an essential component in two enzymes that convert nitrate into nitrite (a toxic form of nitrogen) and then into ammonia before it is used to synthesize amino acids within the plant. It also needed by symbiotic nitrogen fixing bacteria in legumes to fix atmospheric nitrogen. Plants also use molybdenum to convert inorganic phosphorus into organic forms in the plant.

Manganese (Mn) is used in plants as a major contributor to various biological systems including photosynthesis, respiration, and nitrogen assimilation. Manganese is also involved in pollen germination, pollen tube growth, root cell elongation and resistance to root pathogens.

Boron (B) is used with calcium in cell wall synthesis and is essential for cell division (creating new plant cells). Boron requirements are much higher for reproductive growth so it helps with pollination, and fruit and seed development. Other functions include translocation of sugars and carbohydrates, nitrogen metabolism, formation of certain proteins, regulation of hormone levels and transportation of potassium to stomata (which helps regulate internal water balance).

Copper (Cu) activates some enzymes in plants which are involved in lignin synthesis and it is essential in several enzyme systems.  It is also required in the process of photosynthesis, is essential in plant respiration and assists in plant metabolism of carbohydrates and proteins. Copper also serves to intensify flavor and color in vegetables and color in flowers. 

Cobalt (Co) is essential for growth of the rhizobium.  Vitamin B12 which contains Cobalt, is synthesised by the rhizobium and circulated in haemoglobin. The haemoglobin content in the nodules is directly related to nitrogen fixation. Thus a deficiency in Cobalt is shown in reduced Vitamin B12 production and lower nitrogen fixation.

Sodium (Na) is used in small quantities to aid in metabolism and synthesis of chlorophyll. In some plants, it can be used as a partial replacement for potassium and aids in the opening and closing of stomatas, which helps regulate internal water balance.

Chlorine (Cl) is needed in small quantities and aids in plant metabolism, photosynthesis, osmosis (movement of water in and out of plant cells) and ionic balance within the cell.  It is highly essential, combined with the element potassium (K+), for the proper function of the plants stomatal openings. Many people make the common mistake of mixing up the plant nutrient chloride (Cl-) with the toxic form chlorine (Cl).

Nickel (Ni) is a component of some plant enzymes, most notably urease, which metabolizes urea nitrogen into useable ammonia within the plant. Without nickel, toxic levels of urea can accumulate within the tissue forming necrotic legions on the leaf tips. In this case, nickel deficiency causes urea toxicity. Nickel is also used as a catalyst in enzymes used to help legumes fix nitrogen. There is evidence that nickel helps with disease tolerance in plants, although it is still unclear how this happens.

Natural Sources of Plant Nutrients

There are two basic approaches to fertilization. The first is to provide required nutrients to each crop in a soluble form that plants can use immediately, i.e., feed the plant. The advantage to this approach is the opportunity to quite accurately meet a crop’s need. The disadvantage is soluble nutrients do little to build long term soil fertility.

The second approach is building and maintaining a healthy, biologically active soil with large reservoirs of plant nutrients that will provide a crop with its needs. This is the organic approach to fertility and is based upon building soil organic matter, conserving and recycling plant nutrients through cover crops and composting, providing for microbiological activity and adding slow release, natural sources of minerals. Nutrient reservoirs are built over years and then maintained for the most part with compost. The following is a list of materials used to supplement nutrient needs:

Alfalfa meal (2-1-2) A plant based nitrogen source. The nitrogen is released moderately fast.

Blood meal (12-0-0) A very quick-release form of nitrogen with some soluble N for organic growers. Used for side dressing during the growing season. If used in a potting mix the mix should sit a few weeks to avoid ammonia toxicity. Avoid direct root contact as it can burn.

Bone Meal (steamed) (5-12-0, with 22% calcium) An immediately available source of phosphorus good for side dressing early in the season before biological activity gets going. Steamed bone meal has more N than precipitated bone meal, which is commonly used as a feed additive.

Compost (approx. 1-1-1) After reservoirs of nutrients have been built up using rock powders, compost is the choice source of nutrients to maintain levels. It is the best source of stable organic matter for building soil levels. The nutrients are tied up in the organic matter and released evenly over the season. Quality of compost varies greatly as do salt content (very important if using for seed starting) and maturity (important with respect to toxicity of ammonia and nitrogen lock-up).

Fish Meal (9-3-0) An excellent source of slow to moderately released N. The N is tied up in proteins so no risk of burning. The fish odor may attract animals.

Granite dust (0-0-6) Widely used to remineralize soil with micronutrients and potassium. Releases nutrients very slowly.

Greensand (0-1-7 with 3% Mg) A mined rock powder naturally containing potassium that is released over time as the mineral breaks down. Many other nutrients occur in the sand like material (Ca, Mg, Fe, and P).

Gypsum (23% calcium) The choice source of calcium when no adjustment of pH is needed. Also contains sulfur, which, as air pollution is cleaned up, may become a needed nutrient.

Kelp (1 - 5% N, 0.2 - 1.3% Phosphate, 3 - 10% potash, dry weight) In addition to macronutrients, seaweed has a variety of micronutrients, especially boron, copper, iron, manganese and molybdenum. Perhaps the most important merit of seaweed is its organic matter that breaks down quickly in soil.

Dolomitic limestone contains about 25% calcium and about 10% magnesium.

Calcitic limestone contains about 38% calcium. Calcitic is harder to nd. Well stocked stores should carry it because if magnesium is not needed dolomitic limestone should not be used.

Livestock Manure Uncomposted manure offers some bene ts and risks that make its use different from composted manures. It is up to the grower to decide which ts the farm system and particular situation. For example:

Composted manure has nutrients in a stable form which are less likely to shock the system and be less susceptible to leaching.

Contaminants such as livestock medications, weed seeds, and human pathogens are more likely to have been decomposed during composting.

The microbial population of nished compost is very diverse.

Manure will have more nitrogen, especially quickly available nitrogen, than compost.

The different types of manures have important characteristics that the grower must consider. For example, poultry manure contains very soluble nutrients and very little organic matter. This makes it good for a quick boost in fertility (especially P and N) but it does little to build the soil.

Average available N-P-K from farm manures (lbs/T): N P2O5 K2O because if you are after available P bone meal or chicken manure are better sources.

Soy bean meal (6-1-1) Seed meals are preferred sources of N for organic growers because they are the best value except for manure. The nitrogen is moderately available because of the type of proteins (faster than sh meal or bone meal, less quickly than blood meal). There is no risk of burning plants.

Sul-Po-Mag (0-0-22, with 11% Mg) This is a mined rock commonly used as a potassium source in conventional fertilizers. It is the most economical source of available potassium for organic growers. Use only if Mg is needed too. A good source of magnesium if no pH adjustment is needed. The nutrients are immediately available to plants. Only use when crop is growing.

Wood Ash (0-1-5) The potassium is quickly available and so wood ash should only be applied shortly before crop need. Wood ash has two thirds the liming power of limestone and acts very quickly.

Potassium sulfate (0-0-50) Potassium sulfate is available in both natural and synthetic forms and only the natural form is permitted on organic farms. Check with the supplier before purchasing. It is an inexpensive material that adds potassium to the soil without any other cations. It is very soluble and should be used only when crops are growing or it will likely be lost to leaching.

Rock phosphate (0-3-0) Rock phosphate contains about 30% phosphorus but only about 1-3% is available at any time. It is generally used to build up reservoir of phosphate. Rock phosphate has less available P than colloidal but much more total P (colloidal is about 16%). Rock is generally preferred

Selected References

University of Minnesota

Virginia Tech Cooperative Extension

University of Nevada Cooperative Extension

University of Hawaii - Soil Nutrient Management

The role of magnesium in plant disease. Huber, D.M. & Jones, J.B. Plant Soil (2013) 368: 73.

Maine Organic Farmer and Gardner's Association