Deficiency and excess of Calcium in cannabis plants

Calcium and cannabis

First symptoms of Ca deficiency
First symptoms of Ca deficiency

Calcium is a very important secondary nutrient given the large amount of this element that the plant needs during its entire life cycle. From the very beginning, and already in the seed germination stage, calcium takes direct part in root development and protein synthesis. It’s absorbed by the roots in the form of Ca++ ion.

It also gives support to other elements that, when combined, participate in different metabolic processes such as the creation of vitamins - in this case, vitamin B12. These vitamins will join and form part of the cellular walls of the plant tissues, making them stronger to attacks from pathogens, and keeping their cells active and vital.

The role of calcium in cannabis plants

  • Calcium is necessary for the growth of the cell walls of the root system
  • It ‘s an immobile element
  • It enhances the decomposition process of organic matter, improving nutrient uptake by the plant
  • It acts as bridge between humus and nutrients

Intermediate Ca deficiency
Symptoms of intermediate Ca deficiency

Calcium deficiency

Calcium is an element easily found in the soil, so due its high availability for the plants we usually don't find imbalances of this component except in very acidic soils.

Deficiencies can normally be more present in hydroponic crops due to the use of inert substrates (coco-coir, clay pebbles, rock wool, mapito...) or when we don't use substrate, as is the case of aeroponic systems.

In these cases, we must check that the calcium intake of cannabis plants  is correct to prevent deficiencies in the early stages. Many of the fertilisers that we can find on the market have calcium, but sometimes it isn’t enough to avoid deficiencies, particularly if you are using reverse osmosis water, which doesn’t contain nutrients.

In this case (RO) you will have to prepare the nutrient solution in a different way: before adding any other fertiliser, pour two parts of calcium per one of magnesium until reaching an EC value from 0.0 to 0.3-0.4.

Visible symptoms of calcium deficiency in cannabis plants

  • The youngest leaves of the plant are the first to be visibly affected
  • The growth of the upper part of the plant is slowed down
  • The root system is also affected, what reduces nutrient uptake
  • As the deficiency progresses, the youngest leaves turn yellowish and become deformed
  • Bud development is seriously reduced

To control the calcium deficiency we can perform foliar applications of Ca with a Ph of 7.2 directly on the affected leaves. We can also add calcium and magnesium to the nutrient solution, increasing the initial EC value in 0.2 points during about five days.

Calcium excess in cannabis plants

Advanced Ca deficiency
Serious Ca deficiency

The excess of calcium is difficult to detect and causes a lock-out of various nutrients such as potassium, magnesium, manganese and iron. In different hydroponic growing systems, and when there is calcium excess in the tank it comes in contact with the sulphur of the nutrient solution, this calcium precipitates and remains on the bottom of the tank.

In this circumstance, you will have to change the nutrient solution of the tank.

Calcium is an element that is directly related to the transpiration of plants. This transpiration control comes, in essence, from the roots and the stomata, which are located on the leaves. It can happen that the stomata are closed by an excess of heat, causing a superficial burn which could be confused with a symptom of calcium deficiency.

It should also be noted that, with a deficiency of this element, plants are always more susceptible to heat stress given that calcium contributes in the protein creation, which make plants more resistant to high temperatures.

How to supply cannabis plants with calcium

As we have already mentioned, if you are using osmosis water for watering your plants you should add calcium and magnesium before adding fertilisers to the nutrient solution. Since osmosis water doesn’t contain any nutrients, your initial EC value will always be 0.0.

Fertilisers for marijuana plants already contain the necessary micro-elements for the life of the plant, but there are nutrients such as calcium or magnesium which should be present in higher concentrations - especially at the early stages - to ensure that marijuana plants have everything they need to develop properly.

Tap water with an EC range of 0.3-0.4 is perfect, since this EC level is suitable to make the mix with fertilisers and ensure right amounts of Ca and Mg in the nutrient solution. It should be noted that, depending on the grown strain, it may be necessary to add extra calcium and magnesium during the flowering stage to prevent deficiencies from the 4th - 5th week, when plants are in full bloom.

In this case, this extra supply is important so, on the one hand, plants can reduce any kind of stress during the entire crop, and on the other hand we'll harvest the best possible quality and quantity of buds. For these cases you can use Aptus Regulator during the entire crop, reducing the water needs of the plant to up to a 30% while making them more resistant to dehydration caused by high temperatures or periods of drought.

Identifying calcium deficiency in cannabis plants

Ca deficiency in low and old leaves of the plant
Ca deficiency in lower and older leaves of the plant

Example of the condition of a plant with calcium deficiency

Ca deficiency major on the plant of the left side
Serious Ca deficiency (left plant)

The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.

Comments in “Deficiency and excess of Calcium in cannabis plants” (19)


HairyAss 2024-01-17
for mid flowering, around 4-5 week some strains indoors will need 0.5 to 0.6 EC prior using fertilizers, so if you are watering with ec 0.4 and you see calcium deficiency increase it by 0.1 and see how it goes (but before check your PH, if you have low ph in your soil calcium and magnesium will not be absorbed as needed).


Raimundo Is an Alchimia client 2023-10-24
Good afternoon. Some of my plants have red petioles and the stem of the plant. Maybe you can help with advice on what the plants are missing?


Gregg 2023-08-27
I’m I’m my 6th week of flower, buds are growing fat . My problem is that my leaf tips are turning up and brown and I’m getting browning on the outside edges of the leaves. Thought this might be a cal- mag issue . I supplement because I use RO water. Or possibly a ph issue.


Obiwan 2022-04-15
Hmm that sure does look like calcium in excess, it is under the sub category but the pic is labelled as "Serious Ca deficiency" could be misleading

Alchimia Staff

Tim Alchimia 2022-04-19
Hi, thanks for your comment. You're partly correct, the image does indeed look a bit like an excess of Calcium and yes, the positioning of the picture beneath that subheading is a bit misleading, but the image is of a Ca deficiency rather than an excess, although there's very little difference in appearance between the two. Thanks again for your observations, best wishes and happy growing!


Big Time 2021-12-27
I have 6 luscious indica plants in closet under 4 led lights each 1000 watts. They are in their 9th week since sprouting. This week I discovered one plant that has a few green leaves curling up, drying up with no color change, die while still green. Cannot see any pest signs nor fungus, so I guess it’s a nutrient problem. Any thoughts? Appreciate it.

Alchimia Staff

Tim Alchimia 2022-01-10
Hi and thanks for your comment. These dry leaves can have a number of causes, but if the plants are healthy-looking and a nice green in colour then it's unlikely to be a nutrient issue. Check that the affected plant hasn't grown too tall and near to the lamps, as often this can be a sign of light burn. Another cause can be wind burn if the plant is too close to a ventilation fan or the fresh air intake. If both of those options are out of the question, then another possibility is that you overwatered the plant at some point, which can definitely cause this type of symptom, but is relatively simple to resolve and shouldn't cause long-term problems for the plant. Of course, there's always the possibility that the problem is due to some problem in the root zone such as pests of fungal pathogens, so examine the container very closely for any sign of root rot (brown stringy roots) or evidence of pests such as root aphids or fungus gnats, then take the appropriate action if required. I hope that helps, best wishes and happy growing!


Hertronix 2021-10-28
My plant aint looking to good iam in 4th week of flower and the leafes are starting to turn brown ill test my ph tomorrow cause ive been searching everywhere but i couldnt find a deficiency nor Pest or any Type of fungie so iam wondering what it is. now its getting brown from the outside tips looks like mg def but in brown

Alchimia Staff

Tim Alchimia 2021-11-03
Hi, thanks for your comment, we're sorry to hear your plant isn't happy. It's hard to say exactly what the problem could be, but testing the pH would be a good idea so you can rule it out as a cause. At this stage in flowering, it could well be a Potassium deficiency, which shows as brown leaf tips/edges and can be provoked by an excess of Nitrogen or Calcium or too high a pH in the substrate. I hope that helps you sort the issue out, best wishes and happy growing!


Derek MK. 2021-06-25
Should I add water to make a calmag folier spray?? Or just spray as is onto my plants with the calmag ?


Doggiedeb 2020-08-27
I'm in 5th week and I cannot stop the droppy leaves and brown spots.

Alchimia Staff

Tim Alchimia 2020-09-01
Hi, thanks for your comment. Sorry to hear you're having trouble with the plant. With so little info it's hard to say what the trouble could be, but drooping leaves are often a sign of over-watering, which is by far the most common mistake made by inexperienced growers. Overwatering reduces oxygen levels at the root zone and leads to a whole raft of other problems, both nutrient-related and of course, fungal pathogens attacking the roots. Apart from drooping and the brown spots, how are the plants looking? What colour are the leaves? How are they being fed? The more information you give us, the better we can help. All the best and happy growing!


jake 2020-06-25
can tums and epsom salts be used to make cal-mag?

Alchimia Staff

Tim Alchimia 2020-06-26
Hi Jake, thanks for your question. Yes, I've read that you can indeed use them together to correct Cal/Mag deficiencies. From what I've seen online the recipe is 1 teaspoon of Epsom Salts plus 1 Tums tablet per plant. This can be crushed together and applied as a powder around the base of the plant before watering in. If you want to be 100% organic then use a dried, crushed eggshell in place of the Tums tablet. I hope that's useful information. Best wishes and happy growing!


Jandré Swart 2018-07-15
Hate it when no one is talking parts per million. All i want to know is what should my perimeters be for. Calcium Magnesium Kh Ph Temperature of room and temperature of water Nh3 No3 Po4 Kalium/potassium Fluorine Iron Zinc SG. What should their readings be in the water. Growing full on hydroponic system, no soil, any reefers who can relate? I know how to raise and lower these different perimeters. All you need to do is be specific with ppm readings perimeters and stop talking about pre mixed solutions. How do you think experts grow coral? Definitely not pre-mixed part A solution and part B. Man up and Triton test your water. Google it.


Tyson James Schaffer 2018-03-17
No RO water strait up Michigan outta the well at 6.5 pH


Tyson James Schaffer 2018-03-17
Epsent salt is what I have been using threw veg. Stopped in flower now 4-5 week nice buds forming and I see pollen sacks on the bottom branches and they popped iny room. Could the stopping the past few weeks cause this . Only on 1 outta 8 iny tent ..what can I do . I removed all the sacks and thinking giving them a shower ? And ideas to help me flush add a all purpose fertilizer and a few teaspoons of epsent salt per gal. Of pot size .I used a 10 gal pots

Alchimia Staff

Tim Alchimia 2018-03-29
Hi, thanks for your question. It's unlikely that any hermaphrodite traits that you're seeing are caused by the Cal/Mag levels, or by your stopping the Epsom Salts. These things are genetic, this particular plant is simply genetically disposed to produce male flowers. If it's just one plant out of 8 then I doubt it's anything you've done wrong, otherwise you'd be seeing the same problem on more plants. But just in case check for light leaks, check you timer to make sure nothing's accidentally been changed. Keep removing the male flowers, if possible before they open, because once they do it's too late do do anything. As for flushing, just stop feeding two weeks before harvest and just give them plain water until you cut them down. All the best, happy growing!


Dianne hazel 2017-09-10
Hi i also have brown blotches on older leaves. What i read says Cal deficiency shows up in young leaves first. Will flush. Somehow this looks to me more like an overabundance of something. I'm all foxfarm and it started when i added bembe to the mix. Gracias Amiga.

Alchimia Staff

Tim Alchimia 2017-09-12
Hi Dianne, thanks for your comment and question. Flushing is a good start, then check pH, I know Bembe has a high molasses content, which can lower the pH, causing nutrient lockout possibly manifesting itself in the brown blotches, you may need to raise pH a bit. All the best for that, happy growing!


Michael beboper 2017-08-06
If you use organics they are so much more forgiving. It is also living organisms therefore you don't have to rely on expensive nutrients. I do use organic cal mag after flowering and later stage potassium, calcium and phosperua. Organics over the years I have finally found is the most reliable and cheaper too. Bio diverse soils are living soils and if you admend them everything is taken care of. No where near as much money.

Alchimia Staff

Dani Alchimia 2017-08-07
Hi Michael, Thanks for your interesting comment, I think you'll enjoy our article on soil food web gardening! Best!


Tim 2017-05-13
Hi I'm in the 5th week of flowering in nft under leds and growing 3 different types but one of them which is suger haze has these little brown spots and brown blotches on the bigger older leaves it's scaring the shit out a me could it be calcium deficiency new growth and smaller leaves are unaffected ..... thank tim.

Alchimia Staff

Dani Alchimia 2017-05-16
Hi Tim, First thing to do is to flush your plants and make sure there are no salt accumulations in the substrate. Then, you should water the plants with some balanced fertiliser. Also, and depending on the growing medium you're using, add some CalMag additive to your nutrient solution. It'd be important to know what substrate and nutrients you're using. Also, are you using RO water? Talk soon!


Jason 2016-08-25
I need help. Im using ffof and smart pots. Nutes are nectar for the gods. Ph and ppm are in range according to slurry test. Im aboit to flush them with tap water ,theyre in mid bloom and theyre id say semi advanced state. Would i be correct with a good flush and then a idk maybe half doseage of nutes after flush. Is there anything else thatll help this. ? The sooner i get response the better they will be. Please ,please help me!

Alchimia Staff

Dani Alchimia 2016-08-26
Hi Jason, There's no problem at all, some people flush their plants every 2 weeks or so to make sure there are no nutrient accumulations, especially in hydroponic/coco coir crops. Still, have you had any problem with your plants? All the best!


kelly 2016-08-24
I think i have given my plants too much calcium and my garden is dying what do i need to do to fix it??? HELP HURRY PLEASE CAN'T AFFORD TO LOSE ANY MORE PLANTS!!!

Alchimia Staff

Dani Alchimia 2016-08-25
Hi kelly, First thing you should do is fushing the soil generously with plain water a couple of times. Then prepare a light nutrient solution (regulating the pH) and water your plants with it. Excess calcium blocks the absorption of other macro and micronutrients, so the first step is try to get rid of it and then feed your plants with a balanced solution. Are you using pots? Hope it helped!


Papa Indica 2015-09-24
Why did I stop getting email notifications about new blog entries?


Denzidrine 2015-09-14
Good shit yea thanks for the info.

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