Nutrient deficiencies and excesses in Cannabis

It’s inevitable that at some point, almost all cannabis cultivators will find themselves in the position of needing to apply a foliar spray of one kind or another to their plants. There are many potential reasons for this: you could be in need of a fungicide or an insecticide; or maybe you want to fertilise, correct a nutrient deficiency or just give lacklustre plants a bit of a boost.

Whatever the motive for spraying, we think it’s worth doing the job properly, and there are some basic measures we should take every time to make sure we get the best possible results and avoid damaging our plants. We’ll deal with these ten fundamental points first, then go on to talk in a bit more depth about foliar application afterwards.

A small spray bottle working

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Nutrient imbalance in marijuana plants?

In this post we will focus on the macro and micro-nutrients necessary for the development of cannabis plants. These elements are available in the nutrients, so the chosen type of fertiliser and its correct use will lead us to a crop without deficiencies or excesses, thanks to a properly planned and balanced feeding.

There are different factors to take into account, so we’ll try to explain them in a simple way so that all growers can dispel all the possible doubts which may arise relating to the nutrition of their cannabis plants.

What is a deficiency?

Deficiencies are often – although not as a general rule – a lack or inadequate supply of some nutritional element in a precise moment of the plant’s life.

To avoid deficiencies plants must be fed with a complete fertiliser, specially designed for cannabis farming. PH level must be controlled, stabilised and adjusted depending on the type of crop, either in hydroponic or soil crops, and for both potted and in-ground plants.

What is an excess?

Excesses of nutrients are salt accumulations in the metabolism of the plants in a particular stage of their life. To avoid excesses when growing cannabis, we will have to use constant and balanced feeding adapted to each type of culture, substrate and genetics. Each phenotype has its own needs, and to know them ensures best results and avoids nutritional issues.

Table of deficiencies and excesses

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Deficiency and excess of Iron in cannabis plants

Onset of iron deficiency

Iron isn’t a mobile element  and although it isn’t part of the chlorophyll, it does contribute to both the pigmentation and leaf respiration of marijuana plants. Furthermore, it also interacts directly in the enzyme production process. The plant can absorb it in the form of ferric ion (Fe++) although it can also be absorbed organically.

In most crops, deficiencies of this element are usually preceded by a PH value higher than 7.0 in the substrate, in which the plant can’t absorb Iron through its roots. Nor will it be absorbed in very alkaline or chalky soils.

There are other reasons why the plant won’t perform a correct Iron uptake even if it’s present in the substrate: high levels of carbonates, high salinity, constant humidity, low temperatures or excess of other micro-elements that may cause nutrient lockout.

In this case, the youngest leaves – those of the upper part of the plant – will show ferric chlorosis, keeping their veins green. If this symptom isn’t treated, the leaves will become discoloured, with green veins.

Advance of Iron deficiency

Plants use different and varied ways to absorb the Iron contained in the substrate. Through chelating mechanisms – based on the creation of  Siderophores that act sinergically with different bacteria – Iron becomes much more profitable for cannabis plants.

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Functions of magnesium in cannabis plants

Magnesium as mineral

Magnesium is a very necessary secondary nutrient in all the stages of the plants life, and it’s needed in large quantities. It’s the central atom of chlorophyll and has a direct impact on the absorption of solar energy to be subsequently processed and used by the plant in the creation of sugars and carbohydrates.

The cannabis plant absorbs magnesium in ion Mg+2 form, being this the magnesium formulation normally found in most soils. Thus, the absorption of this nutrient will be determined by the available form of this element in the substrate for marijuana plants.

It’s important to find a balance between the available and the unavailable magnesium in the soil. Unavailable magnesium still hasn’t been transformed by the microbial life yet, so plants can’t absorb it. It’s important to know the amount of magnesium available for the plant (which is very difficult to know without analyzing the substrate).

Then, how should we proceed when growing in soil/hydro to have the magnesium levels in the substrate under control? As it’s a mineral, we can supply our plants with it by using a mono-nutrient in Mg + 2 form or other products high in Mg, so we achieve a direct uptake by the roots without having to wait for the microbial life to transform it into assimilable elements for the plant.

Magnesium (Mg) deficiency in cannabis plants

Beginning of Magnesium deficiency

If the Ph range of the substrate is lower than 7.0, then magnesium can be easily absorbed by cannabis plants. But if the soil is very acid – lower than 5.0 – magnesium won’t be assimilable by the plants. In this case, we should increase the Ph level of the substrate by using limestone dolomite. There are other products on the market that contain magnesium in case of not having limestone dolomite to mix with the substrate.

As magnesium is a mobile element, any deficiency of this nutrient will be first visible in the oldest leaves and those of the lower part of the plant. As the deficiency advances, the central part will also be affected.

Magnesium – as nitrogen – is easily flushed through abundant watering. If we wash the roots to solve other other nutrient excesses (N, P, K) we must add magnesium and calcium to maintain a correct nutrient balance. Normally, growers use two parts of Ca for one of Mg (EC=0.4).

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The Phosphorus Cycle:

Before the phosphorus can be used as nutrient for plants, we must wait for Mother Nature to perform its vital functions in order to take advantage of the raw materials that it offers. Phosphorus is an element classified as macro-nutrient since it directly participates – in large amounts – in the metabolism of all plants and especially in cannabis crops.

The phosphorus cycle

The phosphorus cycle is known as biogeochemical cycle, and is a closed cycle which is repeated constantly in a given ecosystem.

Phosphates come into contact with the plant through the ground. Animals eat these plants containing phosphorus, so it’s going to be provided anew to the subsoil in the form of excrements. Later on, it is processed by the micro-life and made available again for the plants (phosphates), thus closing the phosphorus cycle.

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Potassium

There are many nutrients that influence in the development of marijuana plants; on this post, we are going to point out the most important functions of Potassium. We will tell you how to treat deficiencies and excesses of this element and the effect it has on the plant metabolism, especially in cannabis plants.

Potassium

Potassium is an element found in the land in mineral form. This mineral is more or less present according to the type of terrain. Soils composed of clay are by far the richest ones in potassium, containing up to a 3%.

The potassium cycle

This element arrives at the oceans and seas through rain, aquifers, rivers, etc, where it returns by evaporation to the sky in the form of water vapour. This vapour condensates and returns to Mother Earth in form of rainfall..

One of the ways that potassium has for its self-regeneration in the land is through animal droppings. Potassium returns to dry land to be processed again by micro-life. The remains not used by plants will be swept away by the rain and led through aquifers into the seas and oceans to return again to solid ground and close the potassium cycle.

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Calcium and cannabis

First symptoms of Ca deficiency

Calcium is a very important secondary nutrient given the large amount of this element that the plant needs during its entire life cycle. From the very beginning, and already in the seed germination stage, calcium takes direct part in root development and protein synthesis. It’s absorbed by the roots in the form of Ca++ ion.

It also gives support to other elements that, when combined, participate in different metabolic processes such as the creation of vitamins – in this case, vitamin B12. These vitamins will join and form part of the cellular walls of the plant tissues, making them stronger to attacks from pathogens, and keeping their cells active and vital.

The role of calcium in cannabis plants

• Calcium is necessary for the growth of the cell walls of the root system
• It ‘s an immobile element
• It enhances the decomposition process of organic matter, improving nutrient uptake by the plant
• It acts as bridge between humus and nutrients

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Micronutrients in marijuana plants

Bud without deficiencies

In this post we’ll focus on the group of micronutrients that marijuana plants need during their whole life cycle, emphasizing on their main functions and explaining how to resolve and prevent the appearing of deficiencies and/or excesses of these micro-elements.

Generally, if you use a substrate suitable for marijuana culture and a balanced fertilizer, your plants shouldn’t have any kind of excess or deficiency, although it’s always better to know about them to prevent further issues.

Micronutrients are those elements that cannabis plants need in small amounts when compared to macronutrients, which are needed in larger amounts. These elements are necessary for a correct development of the plant’s metabolism, since much of their vital functions couldn’t be performed without them.

Zinc deficiency and excess in marijuana plants

Zinc deficiency

Zinc is a necessary element for cannabis plants because it directly interacts in the creation of the chlorophyll. It’s immediately related to the creation of auxins and growth hormones. It must be noticed that the zinc intake depends on the PH level of the substrate and the concentration of other nutrients. For example, a phosphorus excess affects the intake of zinc.

It’s absorbed by the plants in form of bivalent ion (Zn2+ ), being also easily absorbed from the epidermis and the branches. In soils with a very acid PH level, the roots can’t absorb Zinc and transfer it to the above-ground part of the plant, just as happens  with substrates exposed to low temperatures and a constant humidity caused by rains.

Deficiency Detection/Solution:

• A zinc deficiency is detected by observing the appearance of  chlorosis on the youngest leaves of the plant. Small dots appear on the borders of the leaves, and the plants suffer a very slow development.
• Abnormalities in the development of the leaves, which lengthen. Internodal distance reduction, the leaves tend to make rosettes.
• To solve a Zinc deficiency we can wash the roots to relieve any type of nutrient lockout caused by another element. Then, use fast-assimilation fertilisers rich in macro and micro-elements.
• If the deficiency is severe, spray zinc on the leaves for a greater assimilation by the plant.
• Zinc excess causes a very rapid death to plants due to its high toxicity. Iron deficiency can also be caused by excess of zinc.

Solution to zinc excess: The solution to zinc excess is washing the roots with water and a flushing product, with stable PH. In this way, we clean the substrate so we can start a slight and complete fertilizing schedule with macro and micro-elements.

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Nitrogen (N):

Nitrogen as a nutrient is an important mobile element which is directly involved in the development of marijuana plants during all their life cycle. Depending on the stage of life at which these plants are, they need higher or lower amounts of nitrogen.

This element allows marijuana plants to produce proteins, amino acids, enzymes, chlorophyll, alkaloids and nucleic acids. It is the main cause of growth of the stem, leaves and branches, as well as being directly related to the plant’s vegetative vigour.

It can be found in different forms: organic, ammonium and nitrate. The basic difference between these forms lies in the rate of absorption of nitrogen by the plant, being ammonium the fastest one and therefore the form that can cause an excess of this nutrient more easily.

On the other hand, nitrogen in the form of nitrate is readily absorbed by the plant, although the process is slower. It is for this reason that you can find a mix of both forms in nitrogen-based liquid fertilizers, to balance the nitrogen uptake of the plants and thus avoid an excess or deficiency of this nutrient in your plants.

Nitrogen process

If plants dont’s have a sufficient amount of nitrogen available, they will suffer the lack – deficiency – of it; however, if nitrogen levels are kept too high, your plants will be over-fertilised.

Fertilisers can be of two types: mineral or organic. The mineral form is more rapidly absorbed by plants, for it doesn’t need to be pre-processed by the micro bacterial life that lives in symbiosis with the soil in order to be absorbed by plants. Continue reading →