Deficiencies and excesses in Cannabis

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
Table of deficiencies and excesses

Macro-elements or Macro-nutrients

N deficiency
N deficiency


Nitrogen is the most required macro-element by marijuana plants throughout their life cycle.  A nitrogen deficiency can be easily detected when we observe chlorosis between the veins of the older, lower leafs. If the deficiency isn’t treated, the plant will suffer a massive defoliation and the growth will be seriously compromised.

An excess of nitrogen can be detected by the colour and shape of the leafs of the plants. These become dark green and can adopt a claw-like form, curling down.

P deficiency
P deficiency


Phosphorus is necessary at all life stages of the cannabis plant. The lack of this nutrient is detected in the leafs, which become blue-green and develop brown spots, along with slow growth. The veins and stems turn purple and the leaves curl downwards developing necrotic areas.

An excess of phosphorus usually causes a nutrient lockout which, in turn, causes deficiencies of calcium, copper, iron, magnesium and zinc.

K deficiency
K deficiency


Potassium develops the role of protector against diseases, actively participating in the cellular development along with many other functions. With a lack of potassium, plants are more prone to get all kinds of diseases.

The leaves turn dark green, spots appear and they end up dying. An excess of potassium in plants acts by locking out other elements, resulting in a deficiency of magnesium, manganese, zinc and iron.

Secondary Nutrients

Mg deficiency
Mg deficiency


Magnesium is a secondary nutrient essential for marijuana plants, which is used in large quantities during all phases of the plant life. Deficiencies of this nutrient are usual in soils with a PH value lower than 7.0. Magnesium is the central atom of the chlorophyll molecule, and it is also responsible for enhancing both the absorption of other nutrients and the creation of carbohydrates and sugars.

A magnesium deficiency is initially detected on the oldest, lower leafs, causing chlorosis between their veins, which turn dark green. As the deficiency advances, more and more young leafs are affected by dark spots and chlorosis. If the deficiency isn’t treated, the leaves will curve upwards and, in few days, a massive defoliation will affect the plant.

S deficiency
S deficiency


Sulphur is essential for the production of hormones and vitamins, it’s part of the amino acids and is directly involved in the flavour. A sulphur deficiency causes the oldest leaves to develop a lime-green, yellowish colour. As the deficiency progresses, the leaves turn yellow while keeping their veins green, the petioles turn purple and the stems woody.

Most times, a deficiency of this trace element is usually preceded by a nutrient lockout caused by an excess of calcium or a PH level too high. The solution to this problem is to keep the PH between 5.5 and 6.0 by adding sulphur in ore form for a quick assimilation. If a sulphur excess is produced, we should flush the roots.


Calcium is a very important element for cannabis plants, since they need almost the same amount of macro nutrients than calcium throughout their life. It's essential for the creation and growth of the cells. A Calcium deficiency causes slow plant growth, weak stems and dark green leafs. To treat this deficiency, add some nutrient rich in calcium to the nutrient solution until the deficiency disappears.

An excess of calcium affects negatively to the overall growth of the plant, locking out other elements like potassium, magnesium, manganese and iron. In hydroponic systems, an excess of calcium combined with sulphur causes precipitation in the form of plaster, which remains at the bottom of the tank and clogs the irrigation tubes. In this case, we should change the nutrient solution and carefully check Ca levels.

The most relevant micro-nutrients

Micro-nutrients are nutritive elements which act as catalysts in the metabolic processes of the plants, also in the use of other elements. For a correct use of these nutrients, they should be present in small quantities dissolved in fertilisers.

Zn deficiency
Zn deficiency


Deficiencies of zinc will surely appear when growing marijuana with an excessively alkaline substrate. It acts as catalyst of various auxins, enzymes and is also essential for the growth of the stems. A zinc deficiency is also usually caused by a PH level higher than 7.0, producing chlorosis between the veins of the youngest leaves, which grow thinner, twisted and finally dry out. During bloom, the development of new buds and leaves stops until this problem is solved.

To treat zinc deficiencies we must feed the plant with micro-elements that contain zinc in chelated form to ensure rapid absorption and recovery of the plant.

PH table and nutrient assimilation
Advanced Fe deficiency


Iron is a necessary nutritive element for plants since it’s directly related to the use of energy by sugars. It’s easy to find iron deficiencies in plants grown in alkaline soils. This deficiency tends to be present in soils with a PH level above 6.5. Early symptoms can be observed in the youngest leaves, which turn yellowish while keeping green veins. If the deficiency continues, the plant will suffer serious defoliation.

An iron deficiency can be preceded by a nutrient lockout caused by an excess of copper. Other elements like zinc or manganese can cause a null absorption of iron by the plants, which will in turn cause several deficiencies. To solve an iron deficiency, avoid watering with fertilisers that contain high concentrations of Mn, Zn and Co, and also reduce the PH level of the nutrient solution to 6.0-6.5.

Other micro-nutrients:

Boron: A boron deficiency causes the borders of the leafs to dry and brown, while the shoots are twisted. In the case of an over-fertilisation, the leaves suffer necrosis, causing a severe defoliation on the plant.

Chlorine: A deficiency of this element is rare when using tap water. The leaves take a very characteristic bronzed colour. The symptoms are the same in the case of an excess of chlorine.

PH table and nutrient assimilation
PH table and nutrient assimilation

Copper: This element is actively involved in the metabolism of the plant and in the creation of carbohydrates, also helping in the production of sugars and proteins. In the case of a deficiency, this must be treated by watering with a mineral fertiliser rich in copper.

Excesses of copper, even slight ones, are very toxic. The first symptom is iron chlorosis along with overall slow growth of the plants.

Cobalt: It's difficult to find deficiencies or excesses of cobalt since it is not very important for the development of the plant during its life cycle. When problems of deficiencies or excesses of this element happen, nitrogen will no longer be available for the plants.

Molybdenum: To find deficiencies of this element in cannabis crops is also difficult, since plants need it in very small quantities. When there is a lack of this element, nitrogen uptake is reduced, roots stop their growth and leafs become twisted. An excess of this element, causes plants to show deficiencies of copper and iron.

Silicon: Deficiencies of this mineral in cannabis plants are rare too. A deficiency is detectable by the deformation of new young leaves and an overall decrease of the final weight of the flowers.

The articles published by Alchimiaweb, S.L. are reserved for adult clients only. In France, the age of majority is set at 18 years old. Consult your country's legislation and obey it. Alchimiaweb, SL is a Spanish company governed by Spanish law and can not, in any case, be held responsible for any misuse or non-compliance with the laws and regulations specific to each country, in relation to the articles published on its Blog. We remind you that the cultivation of cannabis seeds on French territory is strongly prohibited by law. We do not encourage our customers to break the law in any way and are not responsible for their use.

Comments in “Deficiencies and excesses in Cannabis” (6)


help needed 2020-02-23
i have a couple of plants in later veg that appears to show signs of K deficiency.4 others are fine , everything the same,execpt tall dark and green. whats a quick aid,as to not cause problems now?

Alchimia Staff

Tim Alchimia 2020-02-24
Hi, thanks for your comment and question. If it's only a slight deficiency then it'll probably be enough to slightly increase the fertiliser dosage for the plants that show a lack of K. You could also check the pH is within the correct parameters and see if you might need to add a little Calcium to improve the uptake of Potassium. I hope that helps. Best wishes and happy growing!


dyan riker 2019-10-22
i can appreciate the detailed info and the time put into this reader.impressed and thankful. you answered alot of questions and filled in plenty of blanks. i will definetley pass on your site to friends and fellow growers


BöhmBred 2019-01-09
Hey Dani Alchimia! This is the first and only comment I've ever left on any site. I just wanted to thank you for how well this website is written and for all the hard work you've put in, not only the work to acquire this wisdom but also to write it down in a comprehensive and simplified manner. This is my go to website for technical information. You've surely given many, many people a little room for blooming!! Some people have green thumbs, others have green blood


Joey Munoz 2017-11-21
Great stuff guys

Alchimia Staff

Dani Alchimia 2017-11-21
Hi Joey, Thanks mate, glad you liked it! Best!


Daniel Ostrander 2016-12-14
How bout a link to where one is? That thing can just not be read...


rossie 2016-08-10
Hi! Thank you for this useful information. Could you upload a larger image of "Table of deficiencies and excesses"? On the small image I can't read the text under each leaves. Thank you.

Alchimia Staff

Dani Alchimia 2016-08-17
Hi Rossie, Done! Can't upload bigger images, I'm sorry!! ;)

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