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Cannabis Plants and Calcium: A Delicate Balance

by | Aug 1, 2022 | Cannabis, Getting Started, Nutrients, Troubleshooting

Calcium is an essential nutrient for your cannabis plants and calcium deficiency or calcium excess can be a problem. If you notice that your cannabis plant leaves are turning yellow, then it’s possible that they have a calcium deficiency. There are some simple ways to fix these problems which we will delve into later. Please continue reading our article to learn what to do if you have a calcium deficiency or toxicity and how to prevent them.

What is calcium?

Calcium is one of the most abundant elements in nature. It’s an alkaline earth metal, and it has a number of important functions within living organisms. It plays many roles throughout our bodies and other living organisms like plants. Calcium contained within plants comes from calcium-containing compounds, such as calcium chloride and calcium nitrate although it is also available in lime and eggshells.

Why do cannabis plants need calcium?

Cannabis plants have a very specific calcium uptake system that they use to absorb calcium into the root zone. As long as there are sufficient levels of calcium in the growing medium, your cannabis plant will absorb calcium and other nutrients through its root system. If there is not enough calcium in the growing medium, your cannabis plants will take calcium from their own stomata, which are on both sides of the leaves and also on the stem.

Calcium is a crucial component of calcium-mediated signaling in the plant kingdom, and it plays an important role in many processes within cannabis plants as it is an essential mineral for plant growth. It plays a critical role in protein synthesis, cell signaling, fortifying the cell walls, and the regulation of gene expression. It is also crucial in helping your plant deal with heat stress. A calcium deficiency can cause stunted plant growth or death. Calcium toxicity causes calcium to accumulate in the leaves and shoots which will eventually kill your cannabis plants if not corrected soon enough. Fortunately, there are many ways to increase calcium levels in your cannabis plants so that they stay healthy which will discuss further below.

Is calcium a mobile nutrient or an immobile nutrient?

Mobile nutrients are nutrients that can move from one part of the plant to the other. Immobile nutrients are the opposite and can only stay in one part of the plant. Calcium is an immobile nutrient, in that once it is in a certain part of the plant it will stay there and can not move the nutrient to other parts of the plant should it become deficient.

Is calcium a micronutrient or macronutrient?

Macronutrients are nutrients that the cannabis plant needs in larger quantities while micronutrients are nutrients that are needed in far lesser quantities by the plant. Examples of macronutrients are NPK, or nitrogen, phosphorus, and potassium. Calcium is a micronutrient in cannabis plants and is needed in far fewer quantities than the above-mentioned minerals. Please note, calcium is still critical to your grow and the plant will still need it throughout the course of its life, especially in the vegetative stage and flowering stage.

What are the symptoms if my cannabis plant has a calcium deficiency?

If calcium levels are too low in your growing medium, calcium deficiency symptoms will begin to show. The first thing you’ll notice is yellow leaves and leaf tips beginning at the bottom of the plant and working their way up toward the top. This calcium deficiency causes a calcium lockout which prevents calcium from being absorbed by plants so they start using calcium stored within their own stomata.

Symptoms of calcium deficiency in cannabis plants include:

  • stunted growth, reduced flower size, and yield
  • yellowing leaves, especially around the edges
  • dead leaf tips curling downwards or upwards
  • wilting despite water being available
  • calcium deposits on stems near damaged areas like pruning wounds
  • yellow or brown spots on the leaves, also called dead spots, and browning of the leaf edges
  • weak stems and branches
  • plants are easily heat-stressed
  • roots turn brown
  • nutrient lockout which can cause a nutrient deficiency in other minerals

How do I fix a calcium deficiency in cannabis plants?

A calcium deficiency is relatively easy to fix. The first thing you’ll need to do is figure out how low calcium levels are in your growing medium. If calcium levels are too low, adding a calcium supplement will be necessary. There are many different calcium supplements available for cannabis growers ranging from regular gypsum, which is calcium sulfate, calcium nitrate, calcium chloride, calcium carbonate, and it can be found naturally in lime and eggshells too. Another option is to use a calcium additive like CalMag, which is short for calcium and magnesium, that contains calcium as well as other essential nutrients such as magnesium and sulfur. This is the simplest way to attack the problem and CalMag solutions are available at most garden centers.

How do I prevent a calcium deficiency in cannabis plants?

Preventing calcium deficiencies is easy and can be done through a few different methods. First, you should always check your pH levels before adding any calcium supplements to the soil. If calcium levels are too low in the growing medium then it may become difficult for roots to absorb calcium even if they exist in abundance which means that growers must first correct their pH levels to make calcium more absorbable. The wrong PH levels will cause the plant to suffer from nutrient lockout and flushing your plant with three times the normal amount of PH’d water should fix the problem. If calcium deficiency symptoms are already present in your plants, the first thing you’ll need to do is apply calcium supplements or a calcium additive like CalMag. If you grow in soil, you can also mix calcium-rich compost into the soil before planting. Finally, calcium deficiencies are commonly caused by calcium being too tightly tied up in alkaline soils so growing cannabis in water-based coco coir would be an ideal choice for preventing calcium deficiency symptoms since it’s a more acidic medium than other mediums like soil or perlite.

What happens if my cannabis plants have a calcium excess?

Calcium toxicity symptoms include spotting on leaves and on the leaf tips. If calcium excess is left unchecked, it can cause calcium to slowly build up in your cannabis plants which will eventually lead to death since calcium toxicity prevents the proper function of plant cells.

Common symptoms of calcium toxicity include:

  • leaf burn also called chlorosis or brown or yellow spots starting on the leaf tips and works its way toward the stem
  • lockout of other nutrients, particularly magnesium and potassium, that will show symptoms of nutrient deficiency
  • eventual necrosis of leaves and then the death of the plant

How do I fix my cannabis plants having too much calcium?

If you have a calcium excess, flush your system with three times the normal amount of PH’d water or calcium-rich compost. You will need to flush your plant with PH’d water and allow it time to recover before harvesting any of your cannabis. If that doesn’t work, you may want to consider transplanting your plants into a new medium with lower calcium levels like coco coir or mixing calcium supplements directly into the soil before planting. Flushing your plant will allow any other minerals that have been locked out to be absorbed by the plant again and hopefully any excess calcium in the medium has been washed away.

How do I prevent my cannabis plants from having too much calcium?

To prevent calcium toxicity in cannabis plants, you can always use calcium-rich compost instead of calcium supplements and the simple fact is that most calcium problems come from too much calcium. If your plants are getting plenty of calcium through water, then there’s no need to add any extra calcium into the system, and doing so would only cause excess nutrients which do more harm than good for cannabis plant growth.

Although some calcium deficiencies can be caused by calcium being locked out of the growing medium, calcium toxicity from excessive levels of calcium is usually a result of growers adding calcium-rich supplements to the medium or nutrient solution and not allowing enough time for plants to absorb it all.


Calcium is an abundant mineral that is used by various organisms for different purposes. For cannabis plants, it is necessary to reinforce the cell walls and photosynthesis, among other functions.

If your plants have a calcium deficiency, you will notice weak stems, the yellowing and then browning of the leaves starting at the bottom, and dark or brown spots on the leaves as the most common symptoms. To fix a calcium deficiency, simply add a calcium-rich substance to your soil or add CalMag, a solution that gives the plants calcium and magnesium. To prevent a calcium deficiency, use CalMag once the plants are old enough or make sure your soil or medium has enough calcium in it.

If your plant has calcium toxicity, you will notice yellowing or browning at the leaf tips that work their way towards the stem. You may also notice other deficiencies, especially magnesium and potassium. All you have to do to fix calcium toxicity is flush your plant with PH’d water, which means running three times the amount of water through your medium. Preventing calcium toxicity requires the grower to not add too much calcium to the soil or growing medium or as a liquid nutrient to the plant.

Thank you for reading our article regarding calcium toxicity, if you would like more information please read our articles regarding magnesium deficiencies or toxicity or potassium deficiencies or toxicity, how to flush your plants, and how to use CalMag.

To learn more about growing cannabis at home consider checking out our guides on: Getting Started, Troubleshooting, and Optimizing your Grow or search our Knowledge Base.

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