Do you have Calcium Deficiency in your Marijuana Plants ?

You may notice some spotting on new leaves on your cannabis plants, yellowing between the veins.

These are some of the first signs to watch out for with a calcium deficiency.

One thing marijuana plants love is calcium, and if you’re not supplementing with enough of it you will run into issues pretty quick.

When lacking calcium in your plants, it can also appear to have an iron or magnesium deficiency.

If you are not sure if your plants are getting enough calcium with their nutrient feeding, there is plenty of information here to give you a definitive answer.

Let’s check out your plants,

Signs of Calcium Deficiency in Cannabis Plants

  • Upper leaf issues show spotting first
  • Lower leaves curl and twist
  • Yellow, brown spots appear on leaf and tips
  • Stunted growth
  • Flower development is slow
  • Brown or dark spots on leaves
  • Random pattern of spots
  • Stems start to become weak
  • Roots have little development
  • The roots begin to die in extreme cases

calcium deficiency marijuana diagram

Why is calcium important to marijuana?

calcium symbol

Calcium is vital for the plant’s growth.

It is an immobile nutrient so the plant cannot find the mineral in older leaves to assist in the plant’s growth.

Calcium in a marijuana plant helps build the cell walls and assists in growing root systems.

It also helps the plant against heat stress.

This secondary nutrient works alongside magnesium, which is also necessary for healthy plant growth.

Calcium deficiency affects all plants.

For example;

You may have noticed if you grow tomatoes in the summer outside without with calcium you get blossom end rot. According to Wikipedia.

Calcium Deficiency marijuana

Brownish spots appearing on a leaf

Causes of Calcium Deficiency

Here is a list of some of the reasons of lacking calcium

  • Not using enough calcium when growing or any at all
  • Growing hydroponically and not supplying enough calcium to the marijuana plant.
  • Low PH soil (check your soil ph values )
  • Using Reverse Osmosis (RO) water, all minerals are removed.
  • This is the best water, you can use for growing. You must supplement with calcium.

You can also run into Calcium Lockout.

Calcium lockout happens when the ph is below a certain level which causes the grow medium to become acidic which stop’s the uptake of calcium by your plants.

Here are some PH values to watch for if they are below these values:

When growing in soil: PH levels of 6.0

Hydro and Soil Less Mediums: PH levels of 5.4


Early signs, yellow spots before they turn brown

How to Fix Calcium Deficiency

If you have determined you are deficient in calcium, then you should start with the following to help your marijuana plants recover quickly.


Flush plants: An essential first step to purge any leftover nutrients


Correct the PH level in water/ nutrients.

The optimal ranges should be in the following markers:

Soil, 6.0 – 6.5 pH range. Hydro or coco coir, 5.6 – 6.2 pH range


Add extra calcium nutrients a little at a time


You could try Dolomite, but a jug of cal mag would do just fine.


Some growers use tap water with great success! Just make sure you over 155 ppm. Most tap water contains calcium and magnesium in small quantities.

Calcium for Marijuana Plants:

Here are some of the popular calcium for your marijuana plants.

Safergro Biomin Calcium can be used for a rapid uptake of calcium in your plants.

It’s only a calcium supplement for your plants.

It also provides vital amino acids to the plant and can be used with soil or hydroponically and is 100 percent organic.


Late stages of calcium deficiency

Cal Mag for Cannabis:

Botanicare CAL-MAG Plus Plant Supplement is the one, two, three punch for your marijuana.

It covers all the bases.

Like Calcium for one and also magnesium and iron, so you know your plants are getting the optimal amounts of supplements they deserve.

Cal mag plus can be used in all stages of growth from vegetative to transition and flowering.

It does contain some nitrogen as well 2-0-0. So be sure to take into account when using any other nutrients.

Cal Mag Plus has 2 percent nitrogen, 3.2 percent calcium, 1.2 percent magnesium, and .1 percent iron.

This can be used in all types of growing : soil or hydroponic

Hydro Organics Earth Juice Elements Cal-n-Mag Plant Food is specifically designed to treat deficiency of calcium and magnesium with your cannabis plants.

It is also a great supplement for any time of the grow and works great in all growing conditions indoors and outdoors, in soil or hydroponic.

Cal-n-Mag contains 2 percent nitrogen and 3 percent calcium and 1 percent magnesium

Advanced Nutrients Sensi Cal-Mag Xtra Plant Nutrient is an excellent combo supplementation which provides the optimal amounts of calcium, magnesium, and iron.

On top of that amino acids specifically designed for marijuana plants.

It’s high on the nitrogen and comes in at a 4-0-0 ratio so take notice when in flower with your other blooming nutrients.

Sensi Cal-Mag is to be used with non-advanced nutrient products as they already had the required amounts of cal mag you need for your plants.

Roots Organics Elemental Supplement comes in  a powder form and can easily be mixed with soil in the beginning or as a top dressing.

Made with natural organic materials like calcite lime, Dolomite Lime, gypsum and fish protein.

Providing your plants with the perfect amount of Cal-Mag and micro nutrients to promote health strong plants.

lower leaf curl marijuana

Lower leaves start to curl

Signs of Excessive Calcium

There are times when your plants cannot handle too much calcium.

It doesn’t happen too often, marijuana likes calcium and eats it like candy.

It still can happen so always manage your nutrients accordingly.

Here what to look out for:

  • Leaf wilt
  • Increased uptake of potassium, magnesium, manganese, iron
  • Stunted growth

marijuana leaf wilt

How to correct excess calcium

The easiest ways to resolve this issue is to simply:


Flush plants which is a great first step


Try and use some balanced nutrients.


Dial down the calcium magnesium supplementation.

Try a little at a time until you start to see improvement.

It could be as easy as a 2 ml per gallon difference.


When growing marijuana always supplement with calcium.

Look for a cal mag combo nutrient to make sure you have the proper amounts.

Getting the right amount the plants require can be tricky but you should be able to fix it before things become too severe.

Calcium deficiency with marijuana can creep up on your plants so be careful and always keep checking your plants for signs of any nutrient deficiencies.

Have you had an issue with calcium with your marijuana?

Let me know in the comments.

Grow on my friends.

image credits: Image , image

18 thoughts on “Do you have Calcium Deficiency in your Marijuana Plants ?”

  1. For Hydro proper uptake of Calcium is done with PH of 5.9-6.5. So the PH has to be on the higher end of the PH spectrum (hydro only).
    I had a Cal def. and raised the PH to 6.3 and seemed to clear right up.

  2. Hi my name is vincent this is my first grow and my plant is 6 days old the sides of the leaves are kinda curling up ? What could it be my plant is only about a inch tall and i have it under cfls about 2 inches away from the lights with a small fan about 6 inches high and six inches wide. What can be going wrong im using fox farm soil also. My ph i dont no what it is cause i dont have one and im using tap water from the sink. Help me

    • Hi Vincent,
      Sorry to here about your plant. I would suggest raising the light to at least 8-12 inches away. 2 inches is way to close. Tap water is ok but get yourself a cheap ph meter for like $15 with PH up / down. And shoot for 6.1 – 6.5. your PH levels are key. Your plant probably doesn’t have a calcium deficiency this early on.
      Hope this helps.

  3. I am deep into the flowering stage – about 48 days – using a 300 watt LED and a couple CFLs on either side of the canopy. I’ve had a growing calcium deficiency throughout the grow, with the concentration being under the LED light. Leaves are crispy and curling, mostly at the top. The sides of the canopy are not as bad, but those leaves and buds have some spotting as well. I wasn’t able to identify the deficiency until a couple weeks ago. I’ve tried Botanicare CalMag, raised the temp to 79 degrees, decreased the humidity as much as possible, but not seeing much relief. I also tried foliar spray of 1 tblsp epsom salts to a gallon of water on a couple areas. I just want to complete this grow, then take precautionary measures in the next grow. What do you recommend?

  4. Hi Vanessa,

    Sorry to hear about your plant deficiency, the good thing is you figured the issue out!
    LED’s really drains you plants of CALMAG
    For this current grow seeing as your 6 weeks in I would start to think about flushing if your using soil.
    Botainicare is excellent I use it all the time . I would recommend for your next grow to use about 2 ml per gallon. You may need up to 5 ml but try 2 to start out with. Add it every time you feed your plants.
    Hope this Helps

  5. Yes, this was a hard one to figure out. The biggest clue was the concentration of damage directly under the LED light. Also forgot to mention that I am growing organically in super soil. This is why I did not want to use Botanicare CalMag, which has EDTA (kills microbes). Do you have a specific name brand for an organic calcium solution?
    Thanks again, Vanessa

  6. Hello,
    I just treated calcium deficiency in my plant and adjusted ph…but leaves keep getting more spots…will it stop and will the plant die?

    • Hi jean
      It may take some time depending on your grow medium. Also watch the new growth and see how it is doing if it is doing ok you should be ok. . The spots should stop over time , the leaf will probably just die off.

  7. hi , new growth is yellow with dark viens . coul this be cal mag def? rdwc system plant is 3 weeks is good hovering at around 6.1 thanks

  8. hello, my bushy plant is now entering its 4thweek into flower and the last top leaves to grow out are showing small poke a dot rust spots not too thickly but sparsely. In soil, 100% organic, and about 12inches away from some Led lights. Could this be calcium deficiency? i havent fed it any during the grow..and if it is how could it affect my bud production?

    • isaac, it could be a cal mag issue , the new led use a lot of cal mag. I would try supplement with a low dose to see if there is an improvement. like 1ml per gallon , Currently I use 3 ml per gallon with de-chlorinated water for coco.

  9. I keep getting the dreaded cal deficiencies too in a recirculating hydroponics system I made! I mix 5 ml / g botonicare cal-mag first into RO water, then add the flora series Nutes in accordance with their nutrient schedule, and Hydroguard. Then pH to 6.1-6.3. After several days 1/3 of the tank evaporated/was used and I added another 5 gal to the 15 gal system. 2 days later I went to add and noticed the pH of the tank was under 5!!!! I raised it but learned the tank pH needs monitoring too. I think the lower pH caused the issue and I’ve corrected. Will that damage continue to develop in the plants until the plants are flushed or should I not see anymore new necrosis once the Nutes are correct? Also, I’m foliar spraying a solution of cal mag daily. Right or wrong when can you see the results of the adjustments? Thanks

    • I hydro growing you can account for a ph drift from between 5.6- 6.3 this is ok and will help the plant absorbs nutes at different ph levels. One you fixed your nutes levels and makes sure ph is in range it should balance out and see a change in a couple of days.


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