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Solving Calcium Deficiency in Cannabis




Calcium is a very vital micronutrient that is needed by the plant for early root development, for proper germination, and all through its healthy maturation into flowering. Calcium aids in ensuring plant vitality as well as strong plant formation. 

When there is a calcium deficiency in cannabis plants, the health of the roots, vitamin and protein synthesis, as well as proper absorption of potassium, and several other plant processes are affected. It would not be wrong to assume that your cannabis plant cannot flourish, and indeed exist without adequate reserves of calcium.


What is Calcium Deficiency?

Calcium (Ca) deficiency in cannabis is a disorder in plants which is caused by an insufficient amount of bioavailable calcium in the medium the plant is growing in. 

In cannabis plants, the function of calcium is to:

  • Help your weed plant develop and maintain healthy and strong stems, cell walls, branches, and stalks. 
  • It is also vital for proper root hair growth as well as the development of the whole root system. 
  • It facilitates transpiration and efficient nutrient uptake.
  • It is required in for photosynthesis 
  • It helps your cannabis plants resist heat stress. 
  • It facilitates the healthy functioning of leaf stomata and hair roots. 


Calcium is generally an immobile micronutrient, which means that it remains in the cell walls where it is initially deposited. However, in very extreme deficiency, it acquires the properties of a mobile nutrient, where it can become soluble again and be moved to where it is needed. This makes it semi-fixed. 


When your plant lacks adequate calcium, it also tends not to absorb potassium efficiently. Calcium deficiency in weed leads to improper functioning of vital processes and if left unchecked, this could pose a serious problem to the plant

How do you Identify Calcium Deficiency in Cannabis?

Calcium acts together with other vital compounds to ensure optimal health and vitality of the cannabis plant. Consequently, when there is a calcium deficiency in weed, the symptoms can mimic the symptoms of other deficiencies as biological functions tend to get compromised.

The following symptoms represent a cannabis calcium deficiency in your weed plants:

Brown Spots on Cannabis Leaves: Large brown spots on cannabis leaves that could be necrotic. The leaf edges also tend to mottle as they turn brown. As the problem advances, the leaves turn yellow. The root system gets compromised resulting in fewer nutrients getting absorbed.

Stunted Growth: The root system gets compromised resulting in fewer nutrients getting absorbed. As the plant processes become compromised, the growth of the plant becomes stunted and loses its luster.

Dead Spots: There are noticeable dead spots all over the plant.

Young Leaves Grow Smaller: Because calcium deficiency primarily affects new growth, any young growth will slow down with the young leaves curling, twisting and dying off. The young shoots may also turn purple.


Other symptoms are:

  • Flower growth gets severely affected. This is more visible during peak fluorescence. The young calyces get distorted and crinkled, and do not fill out.
  • Branches get weak, breaking easily. The stalks of the cannabis plants may become hollow and sometimes even rot inside.
  • Plants stop responding well to heat.
  • The roots of the cannabis plants turn brown and become prone to slimy root rot as well as other pathogens.


Some Strains are more Prone to Calcium Deficiency 

Certain strains of weed have higher chances of suffering from a calcium deficiency than others. Some strains– and sometimes even specific plants in one strain – will have a higher affinity for, and therefore experience a calcium deficiency when the plants around them are thriving. 

Because some cannabis strains (specific plants) use up much higher calcium levels than others, you may notice calcium deficiency problems in them and not in others, even when the nutrients available and environment are the same. 

What Causes Calcium Deficiency in Cannabis?

Several factors may lead to marijuana calcium deficiency in cannabis plants. Below are some of the major factors:.

Using Filtered or RO Water: When a grower uses filtered or RO (Reverse Osmosis) water to feed their cannabis plants, this compromises the amount of calcium available to their plants. Tap water usually has a healthy serving of calcium.

pH is too Low: If the grow medium has a pH of below 6.2, which makes it acidic, it can lock out the absorption of calcium, even if it is actually there.

Not Adding Calcium Supplements in Hydro and Coco: Cannabis grown in hydroponics and coco noir needs constant calcium supplementation.

Too Much Potassium: When your cannabis plants have too much potassium, this can also present as a calcium deficiency. 


Why are you Less Likely to Experience Calcium Deficiency Outdoors?

Typically soil tends to have an abundance of calcium. This means that both plants grown outdoors and those grown indoors in potting soil are not very likely to experience calcium deficiency. Hydroponic setups and cannabis plants grown in other mediums such as coco coir are more likely to experience calcium deficiency because this is an added nutrient that tends to get depleted. 

However, when calcium deficiency in marijuana is experienced in outdoor plants, it is usually because of acidity in the soil. For these reason, it is important to be able to identify signs of calcium deficiency in all as it could occur in any growth medium. 


How to Fix Calcium Deficiency Indoors

The best way of fixing calcium deficiency in weed plants is ensuring it doesn’t happen in the first place. The best way to ensure that is to use a Marijuana Booster which ensures that your cannabis plants are fed adequate nutrients in the right balance for them all through their life cycle. 

In soil

When growing cannabis in soil, growers should ensure that they maintain the PH between 6.0 and 7.0. The absolute best PH for calcium absorption however is above 6.2, therefore maintaining the PH at slightly above the minimum requirement is advisable. 

However, if you find yourself in the position where your cannabis plants are suffering from calcium deficiency, you can apply the following measures:

  • Use products such as garden lime or dolomitic lime. These will not only regularize the PH levels to the ideal ones, they also provide extra calcium in case the soil has a slight deficiency. 
  • You could also use a calcium-magnesium formula, calcium magnesium acetate, or calcium acetate to quickly correct a calcium deficiency. 
  • As we have already mentioned, the ideal PH levels of your soil for the growth of cannabis should be between 6.2 to 7.0.  If you measure the PH of your soil and find that it is unfavorable, first flush out the soil with fresh water which has the correct PH. This water could also contain a boost of nutrients which would restore the balance. 
  • Another compound that quickly fixes calcium deficiency is calcium nitrate (CaNO3). It dissolves very readily in water which allows it to be easily absorbed by the roots. In using calcium nitrate, you should be careful not to use it during flowering as this could lead to your plants having too much nitrogen.
  • Liquid lime and liquid calcium are also absorbed by the roots pretty fast. Just a teaspoon of hydrated lime in one gallon of water will provide calcium that can be taken up easily. 

Last but definitely not least, dolomitic limestone could be incorporated into your planting mix. This is a slow release method that will benefit your cannabis plants over a long period of time. 

In Hydroponics

Water, especially tap water usually contains a good amount of calcium.  As long as the water you are using contains 150 ppm in dissolved solids, you should not fear dealing with calcium deficiency. That said it is usually important to add magnesium and calcium to ensure that your cannabis plants flourish as the cannabis plants could end up depleting the nutrients including calcium in the water.

Just like a soil set-up, PH plays a big role in the absorption of calcium in a hydroponic set-up. Similar to soil, flush out your hydroponic system with fresh water which has the correct pH level with a good boost of nutrients to help restore the balance.

In hydroponics, adding liquid Calcium and lime works well in ensuring the calcium is absorbed fast through the roots. Using a teaspoon of hydrated lime for every gallon of water makes a great calcium feed for your cannabis plants. 

Though it is debatable that you can overfeed your plants with calcium, try to as it might lead to other nutrients being locked out, leading to a different nutrient deficiency. 

In Coco Coir

Just like in hydroponics, the cannabis plants can easily deplete the available nutrients including calcium, and if you neglect to supplement, your plants could suffer from a calcium deficiency. Keeping your cannabis plants grown in coco coir free of calcium deficiencies involves constantly supplementing with the right nutrient mix.

The same steps for supplementing soil can be used to supplement coco coir, ensuring that the medium is flushed to the correct PH.

Though it is often very appropriate to assume that your cannabis plant is suffering from a cal-mag deficiency when it starts experiencing ill health, over supplementing can lead to cannabis calcium toxicity.

Calcium toxicity in cannabis will appear as orange and red spots on the leaves, stunted growth, and drooping leaves, Excess calcium also leads to lockout of other nutrients, whose deficiency will soon begin to show.  As a cannabis grower, you need to be able to differentiate between calcium deficiency and calcium excess as overfeeding them could cause PH fluctuations, lock out and longtime damage to your cannabis plants. 


Stop Calcium Deficiency in Cannabis from Becoming a Problem

The importance of calcium to the cannabis plant cannot be overstated. It is therefore important to look out for any signs that might show deficiencies even before they properly set in, especially if you are using a hydroponic or coco coir set-up.

As they say, “prevention is better than cure!”. Always ensure that your cannabis plants are well supplemented and that they have the correct PH to keep deficiencies at bay and ensure that you have the best harvest possible! 

With the information we have provided, you will be able to spot calcium deficiency in your weed plants from afar and treat it before it becomes a menace. Luckily, calcium deficiency damage is easy to reverse as long as it has not reached the rot stage or severely damaged the cannabis plant. 

Happy growing!


Calcium Deficiency in Cannabis Q&A

What is calcium deficiency in cannabis?

A calcium deficiency is a situation where the cannabis plant is unable to access adequate calcium to enable it to carry out its functions effectively. Calcium is a vital nutrient which aids in providing structure to the marijuana plant, helps in major plant processes, as well as helping the plant withstand stress such as heat stress.

A cannabis calcium deficiency is sometimes difficult to diagnose as they are usually accompanied by other deficiencies such as iron, magnesium, and/or other weed deficiencies.

What are the symptoms of calcium deficiency in cannabis?

You will notice calcium deficiencies in the following places:

  • The youngest leaves will be the first to be affected
  • Dead spots
  • Crinkling
  • Spotting / Mottling
  • Small brown spots on weed plants
  • Growth will slow down in the upper part of your cannabis plant
  • The root system gets affected leading to reduced nutrient uptake
  • As the deficiency intensifies, the youngest leaves could turn yellowish, becoming deformed
  • Bud development gets seriously reduced


How do you treat calcium deficiency in cannabis?

The first step is checking the PH levels of your growing medium and ensuring that they are between 6.0- 7.0, with 6.2 being the most ideal value. PH can be corrected by flushing the medium with water that is of the correct PH, and that contains the correct nutrients to restore the nutritional balance. 

Methods of fixing calcium include:

  • Dolomite lime 
  • Seashells, fish bones, and even eggshells that have been crushed up can provide additional calcium that the plants can access over time.

Once you have treated the calcium deficiencies in your cannabis plants , the leaves as well as the other parts of your plants should start to visibly recover in an average of 5 days. 


Lydia K. (Bsc. RN) is a cannabis writer, which, considering where you’re reading this, makes perfect sense. Currently, she is a regular writer for Mace Media. In the past, she has written for MyBud, RX Leaf & Dine Magazine (Canada), CBDShopy (UK) and Cannavalate & Pharmadiol (Australia). She is best known for writing epic news articles and medical pieces. Occasionally, she deviates from news and science and creates humorous articles. And boy doesn't she love that! She equally enjoys ice cream, as should all right-thinking people.

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