How To Know Which Nutrients are Lacking In A Cannabis Plant?

Nutrient deficiencies can easily be spotted by carefully monitoring the leaves of the cannabis plants. The concrete change of appearance varies depending on the nutrient that the plant is lacking.

Just like any plant, cannabis is susceptible to nutrient deficiencies. Optimal growth and high yield harvest are unavoidable realities for cannabis growers once they can diagnose their plant’s nutrient needs. In dealing with nutrient deficiency, you should equip yourself with the necessary know-how in detecting them.

How To Know Which Nutrients are Lacking In A Cannabis Plant?

Are My Cannabis Plants Lacking Nutrients?

Growing plants require patience and a particular set of skills. One crucial skill is diagnosing what is wrong with them. Common to cannabis plants are nutrient deficiencies. Every grower on the planet is aware that this situation would lead to low harvest or even death of the plants themselves if left unaddressed.

The good thing about cannabis is it can tell us what’s wrong with it through observable defects. Here are the three common signs of cannabis deficiency that should raise red flags to growers:

  1. Leaves discoloration – Change in the leaf color should alert you. Discoloration of leaves is a good indicator that the plant either has a scarce supply of essential nutrients (deficiency) or an overabundance of these minerals (toxicity).
  2. Leaves drooping – This occurs when leaves have become wilt or curled. Eventually, these will drop because certain deficiencies remained unresolved.
  3. Low flower yield – Every grower avoids this unpleasant situation. When a cannabis plant experiences low flower yield, a great explanation would be it lacks nutrients for some time. To prevent this from happening, you should know the type of nutrients your cannabis plants need.

What Macro and Micronutrients Does My Cannabis Need?

Nutrients are necessary to survive and thrive. Such a claim is gospel truth to every living organism. For your cannabis plants to grow the way you expect them to, they need to have a steady supply of macro and micronutrients.

Macronutrients are elements that you have to supply in large amounts. Gardeners are familiar with the macronutrients N-P-K, which refer to nitrogen, phosphorus, and potassium. In humans, protein, fats, and carbohydrates comprise the foundation of a healthy diet. For plants, this is the same by providing an adequate supply of the N-P-K macronutrients.

On the other hand, micronutrients describe trace elements that contribute to the well-being of your cannabis plant. These are magnesium, iron, calcium, sulfur, boron, and others. Daily intake of vitamins and nutrients is essential to the human body. Although taken in small amounts, our bodies will eventually become weak without these essential minerals. This principle also applies to your cannabis plant concerning the micronutrients mentioned.

Before we move on, differentiating mobile nutrients from immobile ones is significant know-how.

As the name suggests, mobile nutrients refer to those essential elements that move throughout the plant to address specific parts’ deficiencies. Phosphorus is a mobile nutrient. If the new growth lacks this element, the plant will transport the phosphorus of the old ones to manage parts lacking it.

Immobile nutrients are the opposite of mobile ones. These elements cannot shuttle across the plant. So, when new growth cannabis leaves lack immobile nutrients, the older leaves could not provide their cached nutrients.

How to Tell if My Cannabis Lack Nitrogen

RAW Nitrogen 20-0-0 - 8 oz

The nitrogen element is crucial for plant growth. Healthy soils possess a suitable amount of nitrogen, promoting plant growth and vegetation. In addition, chlorophyll molecules have nitrogen in them, which are active chemicals in the food-making process of plants.

Because of the pivotal role of nitrogen in a plant’s well-being, it is natural that your cannabis would experience nitrogen deficiency.

Deficiency Symptoms:

Nitrogen deficiency is detected when older leaves exhibit discoloration compared with their younger counterparts. Nitrogen, as a mobile nutrient, explains this scenario. Affected growth appears yellow, which will eventually wilt and fall to the ground. Low turn out of yield will be the long-term result of this defect.

Treatment Steps:

  1. Improve your soil’s nitrogen composition by using blood meal or fish meal.
  2. Adjust the pH level of your soil

If done correctly, you will see improvement in your plant in just a matter of days or within a week. Those yellow leaves will eventually fall, but do not lose hope, for new ones will grow to replace them.

How to Tell if My Cannabis Lack Phosphorus

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Another macronutrient, phosphorus, helps plants in their early stage of root development, stem strength, resistance to diseases, and nutrient absorption. P is found in the DNA at the cellular level, containing the blueprint for cannabis health and growth.

Deficiency Symptoms:

Your plant is lacking phosphorus if you notice that there is slow growth having a weak outlook. Red/purple stems are symptoms, as well, of phosphorus deficiency along with darkening foliage. Since this is a mobile macronutrient, the defect is visible starting between the base and midsection of the plant.

Treatment Steps:

  1. Maintain an acidic pH (near pH 6)
  2. Enhance your soil with fertilizers rich in P. Fish meal or worm castings are sound alternatives.
  3. Provide the required temperature; cold conditions make it difficult for your cannabis to absorb phosphorus.
  4. Ensure that you are not overwatering

The treatment steps require consistency to mitigate the situation. You will see the results of the steps given within the week. When you anticipate the coming cold seasons, it is best to stock fertilizers rich in phosphorus.

How to Tell If My Cannabis Lack Potassium

RAW Potassium 0-0-50 - 2 lb

Last of the big three, potassium has an indispensable role in growing healthy and high-yield cannabis plants. An adequate supply of this nutrient helps the marijuana transport water, sugars, and carbohydrates. This macronutrient also helps in ATP production, which is the cellular unit of energy for living organisms.

Deficiency Symptoms:

Potassium-deficit cannabis may have unusual symptoms. This is because your plant may exhibit average growth and development when it lacks the potassium mineral. Leaves that suffer from potassium deficiency have yellow, brown, or burnt edges and tips. It may seem like a nutrient burn, but eventually, these leaves will turn yellow in their margins.

Treatment Steps:

  1. Ensure that the situation is not a case of a light burn. Adjust the distance of your lighting.
  2. Increase the potassium level of your store-purchased fertilizers. To achieve this, you may use a water-soluble potassium additive.
  3. Correcting your soil’s pH is another practical step. For roots to absorb potassium, your soil must reach a 6.0 – 7.0 pH range.

Once you have done the first step and the discoloration did not spread, it is most likely a light burn. Otherwise, there is indeed a potassium deficiency among your growth. In this case, steps 2 and 3 befit your situation.

What Other Nutrients Are My Cannabis Plants Lacking?

Micronutrients also contribute to the health state of cannabis plants. Thus, it is also possible that your growth will suffer undersupply from these trace elements.


Primarily present in leaves, magnesium is a secondary nutrient that promotes leaf growth. A vital part of the chlorophyll molecule, Mg, directly affects your plant’s ability to absorb light.

A deficiency of magnesium can be seen first in the older leaves. As you have guessed, magnesium’s trait as a mobile nutrient explains this. Discoloration of leaf veins, i.e., having a light green or yellow coloring, is one tell-tale sign of Mg deficiency. Irregular rust-brown spots may also appear, and the stems of your cannabis growth might also become reddish.

This deficiency could become unmanageable if left untreated, costing you the lower leaves of your marijuana plant.

Experienced growers address Mg inadequacy by adding dolomitic limestone in their growing medium. Magnesium sulfate, garden lime, worm castings, and Epsom salts are good alternatives, too. Balancing the pH level should also work.


Considered as a micronutrient, iron helps your cannabis plant to have green foliage. The reason behind this is because Fe is a chief component as photosynthesis takes place. Additionally, the marijuana plant absorbs nitrogen adequately because of the iron nutrient.

An immobile nutrient leaves at the top of your plant will have yellow discoloration that signals iron deficiency. The color may even turn so bright it nearly becomes white. Although somewhat similar to magnesium deficiency, an iron-lacking plant has yellow pigmentation on its new leaves.

To treat this issue, flushing and adding nutrients should be considered. Spraying the affected area with iron chelate is also effective, albeit this solution is a bit temporary. pH stabilization of the soil is another cogent step. For this to happen, you must use soil additives, e.g., compost, elemental sulfur, and fertilizers.


This micronutrient is present in all of the growth stages of cannabis plants. Although its percentage varies based on the growth stage, calcium has the following benefits to your growth:

  1. Nutrient absorption
  2. Cell membrane permeability
  3. Pest and disease resistance

You can pinpoint if your plant is suffering from a calcium deficiency once the new growth has purple or yellow coloring. On average, your plant’s growth is even slow and stunted. The most common giveaway would be the large brown spots on the leaves.

Between outdoor and indoor growers, the latter group has a greater chance of experiencing calcium-wanting plants. The problem commonly lies in the scarcity of calcium in the hydroponics systems of indoor breeders. Practically speaking, this is addressed quickly by adding the nutrient to the water supply. Applying lime to the soil or substrate usually does the trick.


Although cannabis only needs a small amount of this nutrient, sulfur promotes leaf growth, resiliency against diseases and pests, enhancement of metabolism, robust root growth, and vital cellular processes.

Sulfur deficiency is considered relatively rare in the world of cannabis farming. Its most common indicator is the yellowing of the leaves, from top to bottom of the plant. When it comes to the leaves themselves, the discoloration begins at the back, moving to the tips and edges.

Correcting the pH level of your soil is the first step in treating this particular deficiency. The logic is to ensure that sulfur is not locked out.  If you want to find out more about balancing the pH value, check out my post: “What pH value is best for weed plants”. Sulfur absorption is slow, which means a significant result of this treatment may take days.


This element is a vital immobile micronutrient that affects the cannabis plant at the cellular level. Boron plays a central role in building cellular walls. Moreover, in the process of photosynthesis, boron transports the needed sugars (carbohydrates).

Another rare case in growing marijuana, boron deficiency, becomes evident when the upper leaves’ growth becomes stunted and slow. Eventual twisting and wilting follow. The stems are also affected by becoming hollow and rough.

In addressing this inadequacy, growers would flush the growing medium and adjust the pH level until it reaches a desirable range. Providing enough moisture to your plants is a considerable course of action to solve plant issues regarding boron.

Emerald Harvest Cal-Mag Calcium-Magnesium Supplement
Microbe Life Iron Supplement
RAW Calcium/Mag 9-0-0 - 2 lb
Soil Sulfur 4 lb

What is the Role of pH Value in Growing Cannabis Plants?

I assume you have noticed that correcting the pH value is almost mentioned in every nutrient deficiency tackled above. The reason is that an incorrect pH value would affect the holistic well-being of your marijuana plants. Proper pH range leads to a productive yield and vice versa.

In farming, pH refers to the level of acidity and alkalinity of the water supply. Plants need water to survive, so a proper pH level is crucial.

Whether planted on soil or in hydroponics, cannabis plants need to have a suitable pH range to grow healthy, strong, and productive.

Recall that cannabis needs both the macro and micronutrients discussed above. Its ability to absorb these minerals primarily depends on the pH level of the growing medium you are using. Thus, pH imbalances are the common culprits for nutrient deficiencies.

The primary benefit of achieving a well-balanced pH would be a good return on investments because you have ensured a profitable harvest. Visit this post, "How Often Can You Harvest A Cannabis Plant In A Year?" to know more about cannabis harvest.

For soil growers, the healthy pH range would be from 6.0 to 7.0, while those who opt for hydroponics can aim for a 5.5 to 6.5 leeway.

In determining the correct pH for your marijuana garden, you will need an accurate measuring tool. Here are a couple of tools used for pH balancing in mainstream cannabis farming:

  1. pH measurement kit

A regular measurement kit contains a test tube, testing solution, and color-coded pH chart. Here is a step-by-step procedure for using the pH measurement kit.

  • Half-fill the test tube with your fertilizer
  • Add three drops of testing solution to the fertilizer.
  • Gently mix the fertilizer and testing solution through shaking.
  • User the pH chart to determine the pH range of your fertilizer.
  • Do the same steps in testing your runoff.
  1. Digital pH meter

The digital meter is pretty simple and easy to use. Once you have adjusted it to the desired settings, you stick it on your fertilizer, runoff, or soil. Within seconds, you would determine the pH range.

For accurate and up-to-date pH measuring tools, visit this online store.

How to pH Balance the Soil of the Cannabis Plant?

pH imbalances may happen to your soil. The good news is you can do something to troubleshoot this particular farming issue.

First and foremost, you must choose suitable soil. Your substrate should be homogenous, containing the correct elements. The pH level of organic substrates is much more balanced compared with non-organic.

When you choose coco fiber, an inert substrate, you need to pay strict attention to preparing the nutrient solution. Using pH regulators is helpful in this case. If you have digital pH meters, calibrate them according to the pH range for cannabis grown in soil.

Lastly, you can balance your soil’s pH by utilizing organic fertilizers. This type of fertilizer will help you avoid pH swings. You have to be extra careful with mineral-type ones because you would undoubtedly add organisms and micro-organisms for the desired pH range.

For optimal pH measurement, I highly recommend Bluelab Soil pH Pen Meter.

How to pH Balance a Hydroponic Cannabis Growing System?

Growing cannabis plants via the hydroponic technique will demand close monitoring from you. One primary reason for this is because two factors need proper balancing — pH and EC (electroconductivity).

pH refers to the absorption of nutrients, while EC describes the concentration of nutrients.

In the hydroponic growing system, the interaction between the nutrients and the cannabis plants is immediate. It would suggest that the effect of the nutrients on your plant would be almost instantaneous.

To regulate the pH balance of your solution, you must first keep in mind the growth stage of your plants. If they are just at the outset of the growing period, a 5.5 pH would be suitable. This level should gradually increase to 5.9. Once you have reached week 8, your pH should be 6.0, getting to 6.2 in the 10th week.

To determine the correct pH range of your plants in hydroponic, you would need an accurate and precise pH meter. Here let me recommend Bluelab PPM pen.

Cannabis farming requires patience from growers who desire a productive yield. Watching out for any deficiency is a must in order to achieve this. The deficiencies mentioned here should help you become a great cannabis doctor. Good luck with your farming!

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