Calcium Deficiency on Marijuana

Identifying and Solving the lack of Calcium

Marijuana leaf with signs of calcium deficiency

Hi there and welcome (back) to Free the Tree!
In today’s article of our Nutrient Deficiency series we decided to finally cover Calcium Deficiency on Weed.
This is now the third deficiency our plant’s gone through.. I think the issue is with the medium we planted the BBC in, we didn’t give it time to rest..
Regardless, this time around the Big Buddha Cheese plants that had Potassium and Phosphorus  deficiencies now need more Calcium… Loosing a lot of leaf mass which sucks.
Here’s what we’re going to cover

Big Buddha Cheese going through a severe Calcium deficiency

What do plants use Calcium for?

Calcium is one of the 3 main elements that all flowering plants need to thrive. For full disclosure, plants need about 28 different nutrients in order to thrive, most of which are produced by micro-organismes present in the soil.

Calcium is one of the secondary nutrients necessary for plants to grow. Its main use is holding together the cell walls of the plants. When plants don’t have enough calcium new tissue such as root tips, young leaves, leaf and shoot tips often exhibit distorted growth from improper cell wall formation.
Calcium is also used by certain plants to activate enzymes and send signals that coordinate certain cellular activity.

Even though it’s considered as a micro-nutrient, for some plants like tomatoes, calcium is one of the most important nutrients.

We’ll cover this more in detail further down, but Calcium Pectate is not a mobile element, meaning that plants depending on their transpiration process to move it around.

Calcium during Vegetative and Flowering Stages

The use of calcium is the same during the vegetative and flowering stage.
This crucial element is mainly responsible for holding cell walls together.

Stage of LifeCalcium (Ca) Usage in Cannabis
 Whole Life Cycle
  •  Holding Cell Walls, especially in new growth
  • Immobile element
  • Enhances the decomposition process of organic matter which will improve the uptake of nutrients by plants.
  • Acts as bridge between humus and nutrients
  • Activates enzymes and signals that coordinate certain cellular activity
Organic Nitrogen, Potassium and Phosphorus nutrient mixes

What Is Calcium Deficiency?

As the name indicates Calcium deficiency is a sign that the plants roots cannot access the Calcium available or that there isn’t enough available.
Another situation could be that your manganese levels are too high, reducing your Ca/Mn ration.

We won’t go into the technical details here but Calcium and Manganese availability are correlated, meaning that if one is too high the other won’t be as available.

So to recap, Ca Deficiency can occur when there isn’t enough Calcium (less than 40-60 ppm), the pH is off or the level of Manganese (Mn) is too high.

Leaf full of trichomes dying out

At which pH level is Calcium available

As you may know different nutrients are available at different pH levels.
Thankfully for plants on earth, all the nutrients are accessible at a pH between 6 and 7.

Calcium itself is really available to the roots between 6.3 and 9, so if you have an Ca issue aim for a pH around 6.8-6.8

If you want to review the pH levels for each nutrient and how to measure check out our table available in our piece on watering your marijuana plant

The 12 main nutrients necessary for marijuana and their pH level availability

pH levels per nutrient

How to spot Calcium Deficiency on Cannabis?

As we’ve started saying in the intro of this piece, and as it goes with most deficiencies, the signs will show up on the leaves.
To help you out as best as possible we cut this part in 2 sections:

What are the signs of Calcium deficiency?

Depending on how far along the deficiency is and the stage of growth you’re in the signs may differ slightly, especially on the new growth part.
But globally here are the main signs of Ca deficiency

  • Oddly formed new growth; Whether it’s new shoots, leaves or roots
  • Brown/Yellow/orange-ish spots show up all over the leaves, attacking especially the fan leaves.
  • Leaves and stems are very weak; They break/fall off very easily.
  • These spots will grow and the leaf will start to curl up
  • From the tip down the leaf will be brown and dead.

Evolution of Calcium Deficiency

The lack of Calcium is a creeper, the early signs are very subtle and are mostly visible on the new growth, but once it starts being visible on the main leaves it comes in quick and fast.

Here’s the evolution of a couple of our leaves

first signs of calcium deficiency

Early Signs – Orange-like spots appear all over the leaf

Leaf half way dead due to deficiency

Spots widen and leaf starts to die from the tips moving inward

leaf basically dead due to the calcium being extracted

Leaf tips start to curl up as it dies

massive foliage loss

Massive foliage loss as the deficiency advances

How to solve Calcium Deficiency on Weed?

Depending on the reason why you have this calcium deficiency your response will vary.

If you think your soil’s used up and doesn’t contain sufficient levels of Calcium, add a Ca-Mn nutrient mix to your next watering solution.
You should see effects stop within the next week.

In the case where you’re pH levels have been too low, raise them for your next watering (don’t do this too drastically! or else you’ll create pH issues on top of it)

And finally if the issue is related to high Manganese levels you’ll need to add pure Calcium solutions.

To sum up:

Calcium deficiency will show up in the following ways:

  • New growth may be oddly shaped.
  • Brown/yellow spots will appear all over the leaves
  • Leaves will curl up and die
  • Calcium works with Manganese, too much of one and the other isn’t available anymore.
  • After implementing “fixes” deficiency should stop spreading within a week
  • Impacted leaves will not recover

Most Common Reasons for Calcium Deficiency

The main source for Calcium deficiency is pH issues or low quality soil.
As we stated earlier, calcium can be best taken in a pH levels between 6.3 and 9 so if your watering mix is too acidic then it’s not available.
The second main reason for this are soils not containing enough Calcium or too much manganese. In that case just adapt your watering mix as instructed in the previous section of the article.

For quick relief you can also spray the leaves with a Ca concentrated mix about 15 minutes before lights out.
Since Ca is an immobile nutrient the leaves won’t take in much, but just a little will help ^^

That’s it for this one folks.
Until next time, be safe and grow easy!

Have you dealt with Calcium Deficiency?

Share you experience to help out the community! 

A question? Ask the community to help! 🙂

Answeredsagebrush asked 1 month ago • 
123 views1 answers1 votes
AnsweredBill asked 1 month ago • 
101 views1 answers1 votes
AnsweredFloki asked 1 month ago • 
83 views1 answers1 votes
OpenJohn asked 1 month ago • 
80 views0 answers-1 votes

Looking for seeds ? Compare strain characteristics and seed prices 🙂


Strains & Prices

Top Tao Mix 2 Seeds


Strains & Prices

CBD Mix Feminized Seeds


Indica Strains

Texada Timewarp Seeds


Indica Strains

American Dream Seeds


Sativa Strains

Ramses Feminized Seeds


Hybrid Strains

Critical Haze Seeds


Strains & Prices

Durban x C99 Seeds


Hybrid Strains

The Mission Seeds


Hybrid Strains

Toxic Feminized Seeds

See All Strains

You have an Indoor Growing issue? Here's everything we've covered so far

Have a question or want to share?


Join us on Instagram


All pics