Back to top

Nutrients are the compounds that the plant absorbs in order to build its tissues and perform the metabolic activities necessary for its survival. Carbon, oxygen and hydrogen are assimilated by air and water. The rest of marijuana nutrients are taken from the substrate and the nutrient solution. There are different types of nutrients and these can be grouped according to the proportion needed by the plant. In this guide we will group them into macronutrients, secondary nutrients or micronutrients. We will define in detail each of the macronutrients and the typical deficiencies and excesses that may occur.

Primary or macronutrient nutrients: nitrogen, phosphorus and potassium

The nutrients that the plant consumes in largest amounts are called macronutrients and are nitrogen, phosphorus and potassium. All three are mobile, which means that if they are lacking, the plant will take them from other parts of itself. If this occurs, the effects of this deficiency can be identified in the older leaves.

Each of the macronutrients will be analyzed in detail, as well as the typical deficiencies and excesses that may appear.


Nitrogen (N) is the most soluble of the macronutrients, meaning that it leaches the most easily and can be assimilated by the plant most rapidly. Because of this, it is necessary to replenish this nutrient regularly. It often appears in the form of nitrates, and various ammonium compounds. Nitrogen is the major component of growth fertilizers and is necessary for the synthesis of nucleic acids and essential amino acids needed for the formation of new tissue,.

An excess of this nutrient causes an increase in the internodal distance, a stretched or ‘leggy’ growth pattern, with dark green leaf coloration. In addition, the excess growth promotes soft tissue susceptible to attack by insects or fungi.
To solve a problem of excess nitrogen, simply perform a root wash (leach) with twice as much water as the plant container has. We can also leach until the EC of the drainage water is less than 1.6 - 1.8 μS / cm.

A lack of nitrogen causes the oldest leaves to turn yellowish in colour. The nutrient is mobilized from these to the newly formed tissues producing inter- venal chlorosis (yellowing between the veins).
Nitrogen deficiencies produce pale green or yellow plants with little growth vigor.
The deficiencies in this case are easily corrected by adding growth fertilizer to the irrigation.


All living things make use of phosphorus in the form of ATP (adenosine triphosphate), a nucleotide with a high energy bond that is released when the phosphate bond is broken. This element, besides being essential for the energy of the plant, serves many other functions in plant physiology, especially in the production of resin.
ATP is used for photosynthesis, it´s a component of the DNA chain and is particularly essential in germination, cloning, seedling and flowering phases.

Excess phosphorus is often identified late, as the plant makes much use of this element and can withstand high levels. The most notable characteristics of an excess of phosphorus usually present as deficiencies of the elements zinc, iron, magnesium, calcium and copper. The most common symptom is usually the chlorosis of the veins with burns at the tip of the leaves.
To treat phosphorus toxicity, leach with a complete but very soft, (very diluted) fertilizer solution, around 5-10% of the normal amount, using a triple volume of water to leach the volume of the growing medium.

Lack of phosphorus causes developmental delays, with smaller, bluish-green leaves. Necrosis spots will appear and the stems, main nerves and petioles acquire a purple colouration. Later the leaves will start twisting and fall.

It is especially important to look out for a possible lack of phosphorus, since it will cause a delay in flowering, and the flowers will be smaller and not very numerous.

In many cases, the deficiency is caused because the pH of the irrigation water is above 7.00, values at which the absorption of phosphorus is limited.


Potassium, among other functions, is involved in the processes of carbohydrate mobilization, helps in the synthesis of proteins, and is essential in all stages of the plant.
It promotes the development of roots providing more resistance against fungi and bacteria.

Excess potassium is difficult to detect since the effects of toxicity hinder the absorption of other secondary nutrients and trace elements. The plant thus acquires the appearance of a lack of the elements whose absorbtion have been slowed. Likewise, the confusion can be reversed, so that a lack of magnesium, manganese, iron and zinc, leads us to think that there is an excess of potassium. However, this can be corrected by leaching with a solution of complete fertilizer diluted to 5-10%, that is, the solution is prepared by adding one tenth of the recommended dose and using a volume of solution that is three times the volume of the container or planter.

The lack of potassium is not initially detected, as the plants retain their appearance as healthy specimens with small spots of necrosis on the leaves that turn a dark yellow colour and fall after curling upwards.
The deficiency may be due to the accumulation of salts at the root level, since it is present in almost all soils and substrates. To treat the problem is leached to entrain the salts and then a complete fertilizer is added.

2. Secondary nutrients: magnesium, calcium and sulfur 

The secondary marijuana nutrients are magnesium, calcium and sulfur, the salts of which are present in tap water. They are also known as trace elements or microelements, are indispensable in the synthesis of chlorophyll and participate as catalysts in many metabolic reactions. They are needed in very small quantities and it is very easy for excesses to occur. These deficiencies are common occurances in grows in which reverse osmosis water is used. This problem is usually corrected by mixing the osmosis water with running water until the electrical conductivity has a value of about 250 μS / cm.


Magnesium is the element at the centre of the chlorophyll molecule and plays an essential role in the transformation of light energy into vegetable matter. Excess magnesium is not easily detected, but it is also not frequent. When magnesium reaches toxic levels, conflicts with other ions, especially calcium, occur. This is the only real issue it can cause. Magnesium deficiency is common in acid soils, where the pH is less than 7. It produces yellowing between the leaf nerves between the fourth and sixth weeks of growth, although aside from this the plant will appear healthy. Then the tips of the new leaves will burn, and bend upwards. This problem is solved by adding one cup of dolomite limestone to every four litres of substrate in the initial transplant blend or by adding Epson salts at each irrigation.


The calcium needs of cannabis are almost as high as those of the macronutrients. It is the element that maintains the stability of the cellular membrane helping the correct transport of nitrogen and sugars. An excess of calcium prevents the correct absorption of potassium, magnesium, iron and manganese. Special attention should be paid to overfertilization at the beginning of the plant´s life, since it could impede correct development. Deficiencies are fairly common in industrial hemp crops but rare in self-cultivation; they are also quite difficult to detect. Abnormally slow growth is one sign, with yellow areas in newly formed tissues, weak stalks, and an inhibition of correct inflorescence growth leading to a lower yield. To treat a deficiency of this element we recommend a teaspoon of hydrated limestone for every four litres of irrigation water.


This nutrient is essential in the synthesis of amino acids like cysteine ​​and methionine. It is also part of vitamin B1 and many hormones.

Excess sulfur with low conductivity levels usually presents no problems. However, in cases of high conductivities, high levels of sulfur blocks the assimilation of other nutrients.
Symptoms of excess include limited development, small-sized leaves and dark green stems. The edges of the leaves may appear burnt.

To treat this toxicity, a leachate is applied with a very diluted fertilizer solution, ensuring that the volume of leachate is at least three times the volume of the container used.

The deficiency causes the leaves to turn yellow between the nerves, losing turgidity in a similar way to a lack of nitrogen. The tips of the leaves twist down and burn, beginning with the oldest leaves first.
This is normally a symptom of too high pH or an excessive amount of calcium.

The treatment for sulfur deficiency is to lower the pH to 5.5 - 6.0, and add inorganic sulphur to a fertilizer containing magnesium sulfate. Animal manure is a good organic source of sulphur,

3. Micronutrients 

Also called trace elements or microelements, these are indispensable in the synthesis of chlorophylls, and act as catalysts in many metabolic reactions. This group of elements is composed of zinc, manganese, iron, boron, chlorine, copper, cobalt, molybdenum, silicon, nickel, sodium and fluorine. They must be present in minute quantities, and excesses can easily occur. Hydroponic fertilizers are often helpful because they have a balanced proportion of micronutrients. The microelements that are often under the desired limits are zinc, iron and manganese. This deficiency mainly appears in crops whose soil or water has a pH higher than 6.5.

From Kannabia Seed Company, as a marijuana seeds bank, we would like to state the following items in accordance with current legislation in force in Spain:

  1. That cultivation should only be for personal supply and consumption.
  2. That the use and purpose of your cultivation must be therapeutic.
  3. That the plantation should be carried out in the privacy of your own home, similarly the  consumption.

And most importantly, all information that is given references a small cultivation. If you want to buy marijuana seeds, we're the best option for you.


The cultivation of cannbis for self-consumption is an activity subject to legal restrictions that vary from state to state. We recommend consultation of the legislation in force in your country of residence to avoid participation in any illegal activity.

The purpose of this publication is purely informative, horizontal transfer of technical horticultural information.

Kannabia accept no responsibility for any illegal use made by third parties of information published here.