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Calcium is an integral nutrient for proper root and leaf growth. Identifying signs of calcium deficiency in marijuana early in the stages of the nutrient disorder can save the plant's health. If you want to know more about dealing with calcium deficiency in marijuana plants, keep reading!

What Is Calcium?

In terms of plant cultivation, calcium, magnesium, and sulfur are secondary nutrients, or nutrients needed in moderate amounts in relation to primary nutrients, called macronutrients, needed in the largest amounts. 

Primary nutrients include hydrogen, oxygen, carbon, phosphorus, and potassium. Micronutrients such as boron, iron, copper, chlorine, manganese, nickel, zinc, and molybdenum are essential nutrients needed in small amounts compared to primary or secondary nutrients.

Calcium, like iron, zinc, copper, manganese, boron, and molybdenum, is an immobile nutrient, meaning it cannot be redistributed within the plant to new plant growth. For this reason, calcium deficiency symptoms can be found in new growth but can spread to old leaves if not fixed.

How Does Calcium Help Cannabis Plants?

Calcium is an essential nutrient in cannabis plants that helps them grow plant tissues. It is a building block of the plant’s cell walls and membranes. Essentially, calcium is responsible for cell structure and protecting plants against pathogens. 

In addition, calcium provides the following benefits for plants:

  • Improves the absorption of nutrients through the roots and within the plant.
  • Activates several growth-regulating enzyme systems.
  • Improves a plant’s resistance to disease.
  • Responsible for plant cell division and toughening cell walls.
  • Helps convert nitrate-nitrogen into forms required for protein formation.
  • Protects plants from heat stress by promoting respiration.

What Is Calcium Deficiency?

Calcium deficiency in cannabis plants is a nutrient disorder caused by an insufficient concentration of bio-available calcium in the growing medium. Calcium deficiencies are typically found in hydroponic gardens or outdoor gardens with a cool and wet climate and acidic soil.

Signs of Calcium Deficiency in Marijuana

field of cannabis plants up close, calcium deficiency in marijuana

How can you tell if your plant is suffering from a calcium deficiency? Here are a few signs to look out for on your cannabis plants. Keep in mind that these symptoms may also appear for other nutrient deficiencies.

  • Curled leaf tips – In the absence of sufficient calcium, leaves can begin to curl. When you notice “parachute leaves,” you may have this nutrient deficiency.
  • Discolored leaves – Brown or yellow chlorotic spots on the edges or throughout the leaves can likely indicate a calcium deficiency. This may also be a sign of other disorders, so it is crucial to perform a soil test to determine the missing nutrients.
  • Rot – Rot development across new leaves and buds can be a sign of calcium deficiency and root rot. If you spot signs of decay, act fast to prevent necrosis. Necrotic leaves have dark veins.
  • Delayed growth – Calcium-deficient cannabis plants tend to grow slowly. If your plants are taking a long time to reach maturity, test the soil to see if it is lacking calcium.

Causes of Calcium Deficiency in Marijuana

Calcium deficiency can be caused by various issues, including the following:

  • Filtered or reverse osmosis water from the tap may be missing the proper level of calcium.
  • Acidic growing mediums (below 6.2) can cause calcium to get locked out, even if you provide enough nutrients.
  • Growing in hydro or coco-based gardens without calcium supplements can lead to a deficiency.
  • Excess potassium can also be a reason for calcium deficiency. 

How to Fix Calcium Deficiency in Marijuana Plants

If your cannabis plant is suffering from calcium deficiency, here are a few methods you can try to bring it back to optimal health.

Fix the pH 

Calcium deficiency may appear if the roots’ pH is too low. Soil-based gardens should have a pH of 6.2-7.0 to properly absorb calcium. Coco or hydro-based gardens should have a pH of 6.2-6.5 to absorb calcium. Many growers choose to flush their crops with neutral pH water to correct a calcium deficiency.

Dolomite Lime

Calcium deficiency can be corrected with dolomite lime, which has a neutral pH that can fix your soil’s pH. If growing indoors, mix about six teaspoons of dolomite lime for every gallon of soil and then sparsely water with water that has a 6.5 pH. Once wet, mix the soil thoroughly and wait a couple of days before testing the pH. You will need to do this for a few months.

Outdoor growers must follow the manufacturer’s instructions to apply dolomite lime to the growing medium.

Calcium Supplements

Calcium and magnesium deficiencies often show up together in cannabis plants. Because of this, many growers use a Calcium-Magnesium (Cal-Mag) supplement to fix the deficiencies. Growers can choose from liquid, powdered, and organic Cal-Mag supplements. You can see results in under a week.

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What Is Calcium Toxicity?

Feeding cannabis plants too much calcium is not easy to do but can happen. In the event of cannabis calcium toxicity, other nutrients can affect nutrient absorption and create a domino effect of nutrient deficiencies. Calcium toxicity can occur from excess calcium in the growing medium and overfeeding young plants too early or with a high dosage.

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