Cannabis nutrients Part Five: Calcium and Marijuana.

by Alex Robles

My friends on this beautiful day we are going to continue talking about marijuana nutrients by getting into calcium.

Calcium (Ca) is a secondary nutrient that plays a huge part in the health of cannabis plant throughout its life cycle.  It’s involves in different plant processes like photosynthesis but its biggest role is in cell wall development.  That’s an important job because it’s needed for a plants upward and outward growth with strong leaves and branches.  Cell wall development also means a healthy root system that allows for nutrients like nitrogen and potassium to be absorbed from the soil more freely.  Transpiration (the movement of water threw a plant) is affected by (Ca) and helps a plant deal with heat, think of it as a plant sweating.   Calcium is also known to be a semi-mobile element (a majority of the element is locked into the area that it’s deposited in and can’t be moved anywhere else in the plant).


It’s rare to see a cannabis calcium deficiency in soil unless the soil is to acidic or if the plant is being grown in a container and the strain is heavy feeder (a plant that needs more water and nutrients than most other plants its size).   It’s more common to see this deficiency in plants that are being grown hydroponically (soilless i.e. coco coir, rock wool ) or with an aeroponic systems ( bubbling, aerated water ).  The reason for this is because those systems aren’t really designed to hold on to nutrients without some help from microbes.

Since (Ca) isn’t very mobile, the plant can’t pull it from somewhere else within itself if it can’t find it in the soil.  A deficiency will first show up in the newer, upper leaves and will make them look yellow and deformed but overall growth will show down. Photosynthesis and root growth will also slow down without enough calcium.  When the deficiency shows up in the older lower leaves they will get dead spots on them that turn brown and spread over the whole leaf while the tips will start to curl.  Leaves that are getting direct light will also get dead spots because photosynthesis is affected, but this symptom is sometimes confused with heat burn.  If the deficiency is left untreated the plant will begin to wilt and will slowly die from the inside out because the stems will become weak and hollow.  The plant will also lose its ability fight off disease, pests and it won’t deal with heat very well either.

Here are some of the reasons why a calcium deficiency shows up and how to fix it in dirt.

  1. Cannabis absorbs calcium best at a 6.2 – 7.0 pH range but just to be safe I wouldn’t go over 6.5 pH.
  2. Nutrient Lockout will also cause a deficiency. It happens when there are high levels of other nutrients in the soil that block other nutrients from being absorbed.  One remedy for lockout is to flush the plant to break up the nutrient buildup that is on the roots and in the soil.
  3. Make sure your feeding the plant a balanced nutrient mixture for its stage of growth. It could be as simple as double checking the math because sometimes the plant just needs calcium.  Here are a few different ways to add it in.  Top feeding dolomite lime or worm castings is a great source of calcium and magnesium.  Both of them can also be mixed into the soil at about 5 teaspoons for each gallon of soil.

Note:  When you top feed a plant dry soil amendments like worm castings or dolomite lime, it will take about a week them to start to be broken down and absorbed by the plant.  For faster absorption, worm castings can be made into a compost tea.  The damaged leaves will more than likely not recover from the calcium deficiency damage.

If you’re using a hydro system I would replace the reservoir water with fresh water that has the right amount of nutrients and a balanced pH.  I don’t suggest using a compost tea in this type of system because the molasses could clop up the feeding lines.


Too much calcium could make the plant lock out other nutrients and cause other deficiencies.

Well my fellow cultivators that all I have to share about calcium today.

Grow, Learn, Teach

Click here for Worm castings

Click here for pH up down kit

Click here for Digital pH meter

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