Micronutrients and Marijuana plants

Micronutrients in marijuana plants

Bud without deficiencies
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 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.

Boron deficiency and excess in cannabis plants

Boron and marijuana
Boron and marijuana

Boron is a nutrient necessary for the development of many of the physiological functions of marijuana plants, as the formation of the cell wall. This element moves very difficultly through the plant, so deficiencies can be easily observed in the youngest shoots of the plants. However, when Boron is correctly absorbed the younger leaves have twice the amount of this element than the older ones.

Boron is absorbable by the plant only with a stable PH level from 5.0 to 7.0 points. It helps on the stability of other elements - avoiding for example calcium deficiencies - and contributes hormonal processes, such as bloom and developement of the buds. Female flowers facilitate the entry of pollen, achieving a better pollination and seed production.

The excesses of other nutrients, as in the case of the nitrogen, will cause a Boron lockout that translates into a deficiency of this element, what means that even if there is boron in the substrate, it won't be available for the plants.

Deficiency Detection/Solution:

  • Abnormal growth of the young shoots, roots become swollen and stop growing. Burn dots on the leaves of the plants that could be confused with the typical heat burns caused by HPS bulbs . It develops necrosis between the veins; roots become soft, thus facilitating the appearance of harmful fungi. Leaves increase in thickness, developing chlorosis and necrosis.
  • A high calcium concentration causes calcium borate, hardly absorbable by plants.
  • An excess of organic matter causes boron retention in complex forms, which release it very slowly.
  • On sandy substrates with abundance of water, a deficiency can appear due to the ease with which boron is washed from the substrate.
  • In cases of severe drought these elements rise to the substrate by capillarity towards the surface, what makes them inaccessible for the roots.
  • To treat the boron deficiency add a tablespoon of boric acid for every 4 litres of water, or use chelated fertilisers rich in boron.
  • An excess of boron causes yellowing of the leaves. The borders turn brown and necrotic, advancing toward the middle of the leaf. There are insecticides which contain high concentrations of boric acid, so avoid spraying these insecticides on the substrate.

Solution to boron excess: To solve the excess, wash the roots with a stable ph of 6.0, using three times the amount of water than the capacity of the plant pot.

Sulphur deficiency and excess in marijuana plants

Sulphur and Marijuana
Sulphur and Marijuana

A sulphur deficiency is very rare in marijuana crops if a balanced substrate is used. Still, it can be common in poor soils.

In the case of a deficiency of this nutrient, we'll have to make sure that it isn?t a nitrogen deficiency, for it?s very similar in its symptoms: a discoloration/chlorosis of the leaves of the upper part of the plant, which turns yellow. So, an early detection will avoid confusion with a nitrogen deficiency.

As it progresses it can affect at the middle/low part of the plant.


  • Leaves acquire a lime green colour, turning yellowish. The youngest leaves are the first ones to be affected. The stems become woody and purple, and it's followed by an excess of calcium which in turn blocks the absorption of sulphur.
  • This sulphur deficiency is solved by watering with a solution rich in sulphur. If the fertilized is chelated, the absorption of this element is much faster and easier.
  • A sulphur excess causes slow growth in the plant because the leaves develop much smaller, along with chlorosis on the tips and borders if the excess is severe.

Solution to sulphur excess: Wash the soil with triple the amount of water than the capacity of the plant pot, followed by a slight fertilizing, rich in micro and macro-elements.

Manganese deficiency and excess in cannabis

Manganese deficiency in marijuana
Manganese deficiency in marijuana

Manganese is a micro-element responsible of carrying electrons during the photosynthesis process. Manganese is absorbed by the plant through its leaves and roots, and have the capacity of changing its oxidation state and being able, at the same time, to participate in various enzymatic oxyde reduction processes in charge of facilitating the exchange and transport of ions.

Another of its basic functions is taking part in the photosynthesis process, forming part of a manganese-protein responsible for the photolysis of water and creation of O2. It also takes part in other functions, such as co-factor in enzymatic systems with redox-type reactions, decarboxylation, hydrolysis and energy transference, operating as ion bridge of the ATM (Adenosine Triphosphate, the first energy molecule synthesized by the plant).

It also acts in the nitrate reduction phase as a response from the plant to many of the potentials stresses that may suffer during its growing, such as anoxia (deficiency of oxygen), salt excess, drought or nutrition with excess of ammonia.

Deficiency Detection/Solution:

  • Initially, the deficiency is detected on the youngest leaves, advancing to the older ones, with an almost zero growth and a slow bloom.
  • To solve the deficiency , stabilize the PH level of the substrate an water the plants with chelated fertilisers rich in micro elements.
  • An excess of manganese acts by creating orange spots on the leaves that turn brown as it progresses. In addition, there will also be a zinc and iron deficiency caused by a nutrient lockout from the excess of manganese.

Solution to the excess: To solve the excess, wash the roots with triple the amount of water than the capacity of the plant pot, with a stable pH level according to the substrate pH.

The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.

Comments in “Micronutrients and Marijuana plants” (4)


C Hawk69 2020-05-01
What is a cleated micro mix ?

Alchimia Staff

Tim Alchimia 2020-05-07
Hi, thanks for your comment and question. I think you mean a chelated micronutrient mix. Put simply, chelated micro-nutrients are inorganic nutrients (Iron, zinc, copper, manganese, calcium or magnesium) encapsulated with an organic molecule to make them plant-available and also to avoid the nutrients reacting in the soil rather than being taken up by the plants. The roots absorb the chelated nutrients and the chelate releases the nutrient within the plant. Chelated nutrients are also very useful for foliar applications, the chelate enabling the nutrients to pass the waxy layer on foliage. I hope that helps. Best wishes and happy growing!


Sebastian 2018-06-03
Hello, I have some yellow starting to pop up on some leaves from my Sour D plant. I know a little yellow is normal when flowering but I think it could be a zinc deficiency. I bought micro nutrients and started adding it to my water along with Bloom. I’m curious how often I should be adding the micro nutrients to the water and how often the plants need the nutrients. Thank you very much. Sebastian

Alchimia Staff

Tim Alchimia 2018-06-04
Hi Sebastian, thanks for your question. It depends how far through flowering you are. If you're at the beginning then I'd give the micro nutrients in every watering until you see improvement. If however you're in the second half of flowering I'd be a bit more cautious, you don't want to over feed in any way at this point as it can affect the final flavour. I like to recommend at least 2 weeks without nutrients at the end of flowering for the very best flavour. Unless stated otherwise, the doses given on the fertiliser bottle will be adjusted for application in every watering. I hope that's helped, all the best and happy growing!


Jason Miller 2018-02-25
If you have any of your plants any nutrients in excess, how long does it take to flush and correct versus not enough nutrients?

Alchimia Staff

Tim Alchimia 2018-02-27
Hi Jason, thanks for your question. It depends on a lot of factors, but it's always easier for a plant to recover from under-fertilisation than from over-manuring. The stress provoked by too much fertiliser can cause an enormous stress on plants, and with short cycle annuals like cannabis, some badly affected plants may shut down and not recover at all. If however it's just a mild case of over feeding and the plants are still relatively healthy and growing conditions are ideal, give a good flush and it shouldn't take long for the plants to be back to normal health. It also depends on the growing system you're using, in hydroponics the changes will be much more quickly seen, while in soil things will take a little longer as the substrate acts as a buffer against drastic changes in growing conditions. I hope that's helped a bit, happy growing!


ester 2015-08-31
I've noticed that when you go organic with your plant throughout her lifetime, you will not have any of these problems

Alchimia Staff

Dani Alchimia 2015-09-01
Hi ester, If you have a suitable substrate, rich in nutrients and with microbial life, you need very few nutrients - if any - to successfully harvest your plants with no signs of deficiencies. All the best!

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