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Cal Mag Deficiency: Causes, Symptoms and Effective Solutions

Cal Mag Deficiency: Causes, Symptoms and Effective Solutions

Calcium and magnesium (Ca and Mg) are two of the most important nutrients for cannabis plants. They play critical roles in plant growth and development and are essential for healthy and high-quality cannabis crops. However, many growers experience problems with cal mag deficiency, which can lead to stunted growth, yellowing leaves, and reduced yields.

Today, we’ll try to explain to you in a clear way, what cal mag deficiency is, why calcium and magnesium are important for cannabis plants, how plants process these nutrients, and what causes cal mag deficiency. We’ll also discuss how to identify, prevent, and treat cal mag deficiency, and explore the different types of cal mag supplements available.

So, if you are having some trouble managing cal mag deficiency, stay around because once we finish here you will know what cal mag deficiency is, why it matters, and how to fix it!

What is Cal Mag Deficiency?

Cal Mag deficiency refers to a condition where the plant is not getting enough Calcium and Magnesium, resulting in many issues. This condition is common in plants growing in soil with high acidity or low pH, as Calcium and Magnesium become less available to plants in such environments.

Why do Calcium and Magnesium Matter for Cannabis Plants?

Calcium and Magnesium are both macronutrients that plants need in large quantities. Calcium plays an important role in the formation and stability of cell walls and is essential for strong stems, roots, and branches. It also helps regulate nutrient uptake and enzyme activity and can improve plant resistance to stress and disease.

Magnesium is involved in chlorophyll production, which is necessary for photosynthesis and energy production. It also helps activate enzymes and supports the metabolism of other nutrients like phosphorus and potassium.

Without sufficient Ca and Mg, cannabis plants can suffer from a range of problems, including slow growth, weak stems, leaf discoloration, and poor nutrient absorption. Keep in mind that cal mag deficiency can also lead to bud rot, reduced yield, and lower potency.

How Cannabis Plants Process Calcium and Magnesium?

Cannabis plants absorb Calcium and Magnesium through their root systems and transport them through the xylem and phloem to the leaves and other plant tissues. The availability and uptake of Ca and Mg are influenced by several factors, including soil pH, other nutrients present in the soil, and environmental conditions like temperature and humidity.

The ideal Calcium to Magnesium ratio for cannabis plants is generally considered to be around 3:1 or 4:1, although this can vary depending on the growing medium and other factors. In general, cannabis plants require more Ca than Mg, but both nutrients are important for optimal growth and development!

Why Is Cal-Mag Deficiency So Common in Weed Plants?

Cal mag deficiency is a common problem for cannabis growers, particularly those using hydroponic or soilless growing methods. Some of the most common causes of cal mag deficiency include:

  • pH imbalances: If the pH of the growing medium is too high or too low, it can interfere with the availability and uptake of Ca and Mg.
  • Nutrient imbalances: Other nutrients like phosphorus, potassium, and sulfur can interfere with the uptake and use of Ca and Mg by cannabis plants.
  • Poor soil quality: Soil that is low in organic matter or has a high sand content can be deficient in Ca and Mg, making it difficult for plants to access these nutrients.
  • Overwatering: Cannabis plants that are overwatered can experience reduced nutrient uptake, which can lead to Cal Mag Deficiency.
  • Environmental stress: High temperatures, low humidity, and other environmental factors can stress cannabis plants and make them more susceptible to nutrient deficiencies.
Impact of Cal Mag Deficiency on Yield and Quality

The Impact of Cal Mag Deficiency on Yield and Quality

Cal mag deficiency can have a significant impact on the quality of the buds, affecting the levels of terpenes and cannabinoids produced.

Calcium plays a crucial role in terpene production, and a deficiency can result in a reduction in the terpene profile of the plant. Magnesium also plays a role in terpene production, and a deficiency can lead to a reduction in the overall quality of the buds.

On the other hand, calcium and magnesium are involved in cannabinoid synthesis, and a deficiency can lead to lower levels of cannabinoids, which also will end up affecting the potency of the buds.

How To Identify Cal Mag Deficiency in Cannabis Plants?

This can be challenging, as the symptoms can mimic those of other nutrient deficiencies or can vary depending on the severity of the problem and the stage of plant growth. However, there are a few key signs to look out for:

  1. Yellowing Leaves: One of the most common symptoms of Cal Mag Deficiency is yellowing leaves. The yellowing typically starts at the base of the plant and spreads upwards, eventually affecting the entire plant. In some cases, the leaves may turn brown or even black and wither.
  2. Brown Spots: Another common symptom of Cal Mag Deficiency is the appearance of brown spots on the leaves. These spots can be small or large, and they may appear in clusters or spread across the plant. The spots may be surrounded by a yellow halo and may eventually lead to leaf death.
  3. Curling Leaves: Cal Mag Deficiency can also cause the leaves to curl upwards, which is known as leaf curling. The curling typically starts at the edges of the leaves and progresses inward. This can make the leaves look wilted or dry.
  4. Stunted Growth: Cal Mag Deficiency can also lead to stunted growth in cannabis plants. The plants may appear smaller than normal and may not develop as quickly as they should. This can result in a lower yield and smaller buds.
  5. Weak Stems: Another symptom of Cal Mag Deficiency is weak stems. The stems may appear thin and fragile, and the plant may have difficulty supporting its weight. This can make the plant more susceptible to damage from wind or other environmental factors.

Again, note that these symptoms can also be caused by other nutrient deficiencies or environmental factors, such as over or under-watering, pests, or disease. That’s why it’s important to rule out other potential causes before treating for Cal Mag deficiency.

Cannabis Deficiency Stages Chart By WeedStripes
Common Cannabis Deficiency Chart

How to Treat Cal Mag Deficiency in Cannabis Plants

Once you’ve identified Cal Mag deficiency in your cannabis plant, it’s important to take action to treat it. Here are a few methods you can use:

Adjusting pH Levels

pH levels can have a significant impact on nutrient availability in cannabis plants. If the pH of the soil or nutrient solution is too high or too low, the plant may not be able to absorb nutrients properly, including calcium and magnesium. The optimal pH range for cannabis plants is between 6.0 and 7.0, but this can vary depending on the specific strain and growing conditions.

If you suspect that pH levels may be contributing to Cal Mag deficiency, it’s important to test the pH of your soil or nutrient solution and make adjustments as needed. This can be done using a pH testing kit or digital meter. If the pH is too high, you may need to add an acidic solution like vinegar or citric acid to lower it. If the pH is too low, you may need to add a basic solution like baking soda or potassium hydroxide to raise it.

Adding Cal Mag Supplements

In some cases, adjusting pH levels may not be enough to address Cal Mag deficiency. This is where Cal Mag supplements come in. These supplements contain concentrated amounts of calcium and magnesium and can be added directly to the soil or nutrient solution. There are several different forms of Cal Mag supplements available, including liquid, powder, and granular.

When adding Cal Mag supplements, it’s important to follow the manufacturer’s instructions carefully and avoid over-fertilizing. Too much calcium or magnesium can cause nutrient burn, which can further damage the plant.

Top Dressing with Dolomite Lime or Epsom Salt

Another method for treating Cal Mag deficiency is top dressing the soil with Dolomite lime or Epsom salt. Dolomite lime contains calcium and magnesium, as well as other minerals like potassium and phosphorus, and can help balance soil pH. Epsom salt contains magnesium sulfate, which can quickly correct magnesium deficiencies.

To top dress with Dolomite lime, simply sprinkle a small amount over the soil surface and water in. For Epsom salt, dissolve a tablespoon of the salt in a gallon of water and apply it to the soil. Be sure to use caution when top dressing, as too much can cause a nutrient burn.

How to Prevent Cal Mag Deficiency

While treating Cal Mag deficiency is important, preventing it from occurring in the first place is the best strategy. Here are a few tips for preventing Cal Mag deficiency:

Use Quality Soil or Nutrient Solution

Using quality soil or nutrient solution that contains adequate levels of calcium and magnesium is the first step in preventing deficiency. Look for soil or nutrient solutions that are specifically formulated for cannabis plants and contain the right balance of nutrients.

Understanding Proper Calcium and Magnesium Ratios

The proper ratio of calcium to magnesium in cannabis plants is important for healthy growth. While the ideal ratio can vary depending on the strain and growing conditions, a general rule of thumb is to maintain a ratio of 3:1 or 4:1 (calcium to magnesium).

This can be achieved by using a nutrient solution or soil that contains the right balance of nutrients.

The Impact of Environmental Factors

Environmental factors like temperature and humidity can also impact calcium and magnesium uptake in cannabis plants. Maintaining consistent growing conditions can help ensure that the plant is able to absorb nutrients properly.

Temperature should be kept between 65-80 degrees Fahrenheit during the day and 55-75 degrees Fahrenheit at night, while humidity should be kept between 40-60%.

Factors Affecting Calcium and Magnesium Uptake

Factors Affecting Calcium and Magnesium Uptake

When it comes to the factors that affect their uptake in the body, there are several things to consider:

  • Vitamin D levels: Vitamin D is necessary for the absorption of both calcium and magnesium in the gut. Without enough vitamin D, the body cannot properly utilize these minerals. Therefore, it is important to get adequate sun exposure or supplement with vitamin D to ensure proper absorption.
  • Dietary intake: The amount of calcium and magnesium in your diet can impact their uptake in the body. Foods that are rich in calcium and magnesium, such as dairy products, leafy greens, and nuts, can help ensure that you are getting enough of these minerals.
  • pH balance: The pH of the intestines can also affect the absorption of calcium and magnesium. If the pH is too acidic or too alkaline, it can interfere with their uptake. Therefore, it is important to maintain a healthy pH balance through proper diet and lifestyle habits.
  • Medications: Certain medications can interfere with the absorption of calcium and magnesium. For example, some antacids and laxatives can decrease the uptake of these minerals. If you are taking any medications, it is important to speak with your healthcare provider to ensure that they are not interfering with your nutrient uptake.
  • Age and health status: As we age, our bodies may become less efficient at absorbing calcium and magnesium. Certain health conditions, such as Crohn’s disease or celiac disease, can also interfere with the uptake of these minerals. If you have any health conditions or are concerned about your nutrient uptake, it is important to speak with your healthcare provider.

Different Types of Cal Mag Supplements

Cal mag supplements are a popular solution to prevent or overcome calcium and magnesium deficiencies in cannabis plants. There are various types of cal mag supplements available, such as liquid, powder, or granular forms. Each type has its pros and cons.

Liquid Cal Mag Supplements

These types of supplements are easy to use and quickly absorbed by plants. They are suitable for hydroponic systems, where nutrient uptake is faster than in soil. However, liquid cal mag supplements are expensive compared to other forms and require frequent application.

Powdered Cal Mag Supplements

These ones are cheaper than liquid supplements and can be easily mixed with other nutrients. They are also suitable for soil and hydroponic systems. However, they can be difficult to dissolve in water, and overuse can cause nutrient burn.

Granular Cal Mag Supplements

Finally, these supplements are slow-release and can provide long-term nutrient availability to plants. They are suitable for soil systems, where nutrient uptake is slower than in hydroponic systems. However, they can be challenging to apply and distribute evenly, leading to uneven nutrient uptake.


Calcium and magnesium are essential nutrients for cannabis plants, and their deficiency can lead to a range of issues affecting plant growth and harvest yield. It is crucial to maintain optimal soil pH and nutrient balance and to supplement with cal mag supplements when necessary.

By monitoring nutrient levels and seeking expert advice when needed, growers can ensure their cannabis plants receive the necessary nutrients to thrive and produce high-quality buds.

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