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Calcium Deficiency

calcium deficiency cannabis
Posted by: Samuel Thomasino Category: Plant Problems Comments: 0

Calcium Deficiency

Calcium deficiency can be a common issue for cannabis growers, you may have already experienced this or are curious of the signs to look out for to ensure your plants do not become deficient. Calcium is crucial for the growth of any plant, including cannabis. This article will discuss why calcium is needed in cannabis plants, the signs of a calcium deficiency, how to treat a deficiency, potential causes and also the risks to cannabis plants if a calcium deficiency is left untreated.

The most common reason for Calcium defiency

Here is a great example of how many growers can face either a Calcium or Magnesium deficiency. Growing in an area with hard water such as Nottingham means Calcium and Magnesium are both present in the tap water. Many of the locations in the UK with higher population rates have hard or moderate water. But in the South West such as Cornwall the water is soft and does not include Calcium or Magnesium. Food such as Canna does not include Calcium or Magnesium as standard so using this food in a soft water area will result in deficiencies and ill plants. For soft water areas, the grower must add a Calmag supplement, which is a blend of both Calcium and Magnesium, to their nutrient mix themselves. Either this or use a nutrient that is designed for soft water.

hard and soft water graph

Hold up! You may not need to add more nutrients to your plant

The majority of growers do not need to add more specific elements to their nutrient mix. Most people experience bad leaves and deficiency symptoms on their cannabis plants due to either bad PH levels in the medium or stress which causes plant lockout. Plant lockout means the plant has experienced too much stress and as a result has stopped uptaking nutrients. Once this happens all sorts of 'false' symptoms could start showing. Regularly checking the PH run-off from soil, coco or rockwool will let the grower see if there is a PH problem. Hydro setups can massively fluctuate PH levels depending on the design, so this could also cause plant lockout. Check out our guide on what causes plant lockout and how to fix it for more information.

As mentioned above the PH of the soil or hyrdro system is vital for ensuring the plants are able to uptake the nutrients required for optimal growth and development, if the PH becomes too high or too low then the rooting system can become compromised which affects how the plant can uptake nutrients.

Function of calcium in cannabis plants

Cannabis plants require a wide range of nutrients for successful growth, calcium being one of these. Calcium plays a vital role in a plant’s development and a deficiency can cause damage. One function of calcium with any plant is that it’s been proven to support the plant against microorganisms such as fungi and bacteria that can cause damage to the plant, calcium also supports early root growth and germination. Calcium supports the development of the cell walls and membranes which are responsible for rigidity and strengthening the plant, calcium is also responsible for activating enzymes responsible for cellular activities. Calcium also supports the absorption of other nutrients, such as iron and magnesium, if there is a calcium deficiency the cannabis plants will most likely also experience a deficiency in either iron or magnesium as a direct result of the calcium deficiency. Calcium also protects the plant against some environmental issues as it is involved in activating mechanisms within the plant to allow the plant to adjust to conditions that could otherwise cause potential damage to the plant, such as extreme temperature changes or drought.

Signs of calcium deficiency

Usually the first signs of a calcium deficiency will be noticed in the new growth or younger leaves closest to the lights. One sign of a calcium deficiency is brown spots appearing on leaves that generally start toward the middle of the leaf. In some cases the leaf can also begin to appear yellow, however, this is not always the case. The new growth will tend to curl under and potentially fall from the plant, stems can become weaker and are prone to breakage. The plant will also be more vulnerable to environmental factors such as cold and heat. The plant will also struggle to uptake nutrients due to the compromised rooting system. Calcium deficiency will also slow the overall growth of the plant, including the buds.

Pictures of calcium defiency

Here are a few pictures of a cannabis calcium defiency in both early and late stages
early calcium deficiency

early calcium deficiency

late calcium deficiency

How to treat calcium deficiency

Once a calcium deficiency has been determined its important to act swiftly to ensure the survival of the plant. There are a number of ways to treat a calcium deficiency, one of the first actions to take would usually be to check the PH of the soil or the water system, if the PH is too acidic then the roots are unable to absorb calcium and other nutrients, the system can be flushed through if needed until the PH is around 6 (depending on the medium you use). PH water and a complete cannabis nutrient mix would be used to flush through the system. Another option is to add more calcium into the system, keeping in mind that magnesium and iron deficiencies are directly linked to calcium deficiency, so a mixture of these nutrients may be required for the best outcome for the plants. Once the deficiency has been rectified new growth will begin to come through displaying healthy leaves and stems etc, the damaged leaves from the deficiency will remain damaged. Growers would continue to monitor the plants and the PH to ensure the deficiency has been corrected.

Risks to cannabis plants if a calcium deficiency is left untreated

The risks of calcium deficiency can be extremely damaging to cannabis plants, growers should act swiftly once noticing a deficiency. Due to a calcium deficiency the leaves will begin to curl under and start to drop from the plant, stems will appear hollow and will bend and break. New growth is most vulnerable and the plant’s growth will slow down. The rooting system will begin to fail and the plant will be unable to uptake any nutrients which will then cause further damage, the plant will then begin to display symptoms of other nutrient deficiencies and will continue to weaken until the plant perishes.


To conclude, a calcium deficiency can be a common occurrence in cannabis plants and its effects can be extremely damaging to plants. Calcium is vital for the growth and development of early roots, stem rigidity, cellular activities and protects cannabis plants against harmful microorganisms. Growers should closely monitor their plants for signs of deficiencies and act accordingly to rectify the issues.

This article is for informational purposes only and under no circumstances should be taken as legal or practical advice.

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