Calcium deficiency in marijuana plants

Calcium helps your marijuana plant have healthy and strong cell walls, stems, branches, and stalks. It also helps out with root hair growth and root system development. If your weed plants have calcium deficiency, your plant won’t be able to absorb potassium properly, either. Calcium also helps your plants handle stress factors, such as very warm temperatures.

If your plant has a calcium deficiency, this process will not be able to function properly, and it could lead to more serious problems if left unchecked. Make sure to take care of it as soon as you notice some calcium deficiency symptoms.

Learn more about how to provide your cannabis plants with the proper nutrients when you download my free Grow Bible.

Signs of a calcium deficiency

If you’re growing marijuana plants outdoors, it’s unlikely for them to become deficient in calcium. The likelihood of it happening increases if your plants are growing in very acidic soil, which is often the case in pinewoods.

signs of calcium deficiency in marijuana

Sometimes plants growing in planting mixes will experience a lack of calcium, but most of all it happens to marijuana that is growing in a hydroponic system. Unless your hydroponic system has had lime, a huge source of calcium, added to it, then a calcium deficiency is not uncommon.

It also is more likely to occur with some sources of water rather than others. Distilled water, reverse osmosis water, and tap water often don’t contain much-dissolved calcium – they need to be supplemented in order to provide your plants with enough calcium from the beginning.

Certain strains of marijuana have higher chances of experiencing a calcium deficiency than other strains. Some strains– sometimes even some specific plants within one strain – have more calcium than the plants next to them. This means it is not uncommon for one plant to exhibit signs of a calcium deficiency while the rest of your plants are happy and thriving.

It is always better to not have any nutrient issues in the first place ofcourse! By using my Bergman’s Plant Food, created specifically for marijuana plants, you will ensure a great grow!

buy marijuana fertilizer set

All-in-one nutrient package

  • All the nutrients from seedling to harvest
  • Enough nutrients for at least 5 plants
  • Specifically balanced for marijuana plants
  • Suitable for soil, hydroponic and other growing mediums

Also LED lights offer a smaller spectrum of light. Certain wavelengths the plant requires to generate calcium are absent. So keep an eye on calcium deficiency when growing with LED.

When do signs of calcium deficiency begin

Calcium is a semi-mobile nutrient, so the signs of a calcium deficiency begin with the new growths on your plant, but they will start moving after a period of time. You will first see it in the new growths towards to top of your plant as well as the middle vegetative growth. This is simply because it appears first in the area that is growing the fastest.

If you test out the pH of the plant’s soil and see that the pH level is too low, then adding calcium to it will not be a bad idea. 

How to fix a deficiency in soil

The best way to fight it is to avoid it in the first place. The best way of doing that, like with other nutrient deficiencies, is to use Marijuana Booster to ensure your plants are fed with the right nutrients at the right times.

fix calcium deficiency in soil marijuana

If you weren’t able to avoid it and you have found yourself dealing with a calcium deficiency, there are options. Some possible products you can use are dolomitic lime or garden lime (located in potting soil and planting mixes). They will help stabilize the pH levels of your system as well as providing your plants with calcium.

One other option is using a calcium-magnesium formula, calcium acetate, or calcium magnesium acetate to quickly relieve a calcium deficiency. PH levels of your soil should be between 6.2 and 7.0.

How to Fix Deficiency in Soil
How to fix deficiency in soil

Read the article How to measure the pH of your soil to learn how. If it isn’t around 6, flush out your system with fresh water that has the proper pH level as well as a boost of nutrients to restore the balance.

There is another compound that can help quickly with a calcium deficiency: calcium nitrate, or CaNO3 (wiki). It dissolves easily in water and is therefore easily absorbed by roots. Just be careful: don’t use calcium nitrate while your plants are in their flowering stage because it will make them have too much nitrogen.

Other products to consider are liquid calcium and liquid lime, which roots can also take in very fast. One teaspoon of hydrated lime per gallon of water is perfect for the fast-acting uptake of calcium. Another option is to mix in dolomitic limestone with your planting mix. This will help over a greater amount of time, rather than just being a quick fix. These products can be bought at this online grow shop.

Fixing a deficiency in hydro

Fixing a calcium deficiency is a crucial piece of knowledge for any hydroponic grower, since they happen much more commonly in this case. Since water naturally contains a certain amount of calcium, hydro fertilizers often don’t contain very much calcium.

Fix calcium deficiency in hydro marijuana
Fix calcium deficiency in hydro marijuana

As long as your water has more than 150 ppm of dissolved solids, then calcium deficiency should not be a problem for you. If it has less than 150 ppm, then it’s probably a good idea to add some calcium and magnesium to make sure your plants will receive enough of these nutrients to thrive.

Also read How to measure PH and PPM for your marijuana grow

The pH level also comes into play with a calcium deficiency in a hydro setup. If the pH level is outside the range of 6.2 to 6.5, you are more likely to have a calcium deficiency than if it is within this range. Flush out your system with fresh water that has the proper pH level as well as a boost of nutrients to restore the balance.

Plants with strong genetics have less chances of getting sick. We have an all-in-one care package for you: Bergman’s Complete Grow sets!

buy all-in-one marijuana grow set

All-in-one grow kit

Calcium and lime in their liquid forms work well for fast absorption into the roots. Try using one teaspoon of hydrated lime per gallon of water and feed that to your plants. You will quickly see the results.

Although feeding too much calcium marijuana plants in any system is unlikely, make sure you don’t feed them so much they lock out the other nutrients. Otherwise, you will end up dealing with another nutrient deficiency straight away! Get your nutrients at my favorite online grow shop

How to fix a deficiency outdoors

If you’re growing your plants outdoors and you’re working with soil that is acidic, try infusing calcium into that acidic soil. This will help the soil become a more ideal pH level – between 6.0 and 6.5. You can use dolomitic lime, garden lime, fish bones, seashell, or ground-up egg shells to accomplish this and make sure your soil has plenty of calcium for a longer period of time.

fix calcium deficiency outdoors marijuana

Another option for outdoor growers is using gypsum or calcium sulfate (wiki). Be aware of your soil’s current pH level before you do this, however. If it is below 5.5, don’t add gypsum at all because it then interacts with aluminum (Al) and will poison your plants! Gypsum is a good option for people who have tested their outdoor soil and see that it is within the ideal range since gypsum doesn’t mess with the pH level very much.

List of marijuana plant symptoms

Leaf color:

  • Leaves’ green color darkening
  • Large, light brown necrotic spots

Leaf symptoms:

  • Spotting and mottling
  • New leaves are small and distorted
  • The tips of leaves curl
  • Leaves are dying off
Leaf symptoms of a cannabis plant with calcium deficiency
Leaf symptoms of a cannabis plant with calcium deficiency

Plant symptoms:

  • Flower or bud development is slow or buds never fully develop
  • Stunted growth
  • Young shoots are crinkling
  • Young shoots are discolored – purple or yellow
  • Stems and branches are weak, easily broken
  • Stems are hollowing out or decaying from the inside
  • Plant doesn’t withstand heat well

Root symptoms:

  • Roots may begin dying off or turning brown
  • Root systems not fully developed
  • Root diseases and bacterial diseases
  • Roots more vulnerable to slimy root rot
Root symptoms on a marijuana plant
Root symptoms on a marijuana plant

Calcium deficiencies can sometimes be tricky to spot because they often come with other deficiencies – especially in magnesium and iron. Because of this, lots of growers will buy a calcium-magnesium (“Cal-Mag”) supplement to have on hand, in case they see signs of a calcium deficiency within their grow room.

FAQs about cannabis calcium deficiency

How do I know if my plants are deficient in calcium?

Among the symptoms you should look out for are changes in leaf color (you’ll notice light brown spots), plant symptoms like stunted growth and weak stems and branches, and root rot.

How do I fix cannabis calcium deficiency in a hydroponic setup?

Use fresh water with a proper pH level to flush out your system. Make sure to add a boost of nutrients as well to restore the balance.

What’s the best way to add calcium to the soil of my weed plants?

Compost can be helpful as it is generally high in calcium content. Alternatively, you can amend it by adding lime or eggshells to increase calcium levels in the soil of your marijuana plants.

Want to be an expert in cultivating marijuana? Practice and learning are all you need! Our blog is an extensive cannabis growing resource.

Have you grown cannabis plants that had calcium deficiency? How did you manage it? Please share your experience or leave questions below!

Happy growing!


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Mr Robert Bergman PhD


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

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16 comments on “Calcium deficiency in marijuana plants”

  1. I Am close to flushing my plants should I add calcium to the plants? They are showing signs of calcium deficiency but I’m not sure if I should add more nutrients since I’m so close to flushing them.

  2. Francesca,

    Once a leaf has as much as 60% damage to the leaf; It is best to remove it. The plant will waste energy attempting to heal the leaf. Once gone energy can be used by the plant normally. – I❤️GM

  3. Should we pick off all the affected leaves? I am nervous to trim too much and then stress the plant….

  4. Thanks Dickie. Robert’s not in so I added a line myself. It’s a rather complex story about the ionisation of the calcium which I did not want to get into atm. If you have any info for me I’m all ears 🙂

  5. It is always advisable to have some CalMag on hand. The Marijuana Booster is a full range nutrients and should be OK as a stand alone nutrient system. However; If you have a Calcium deficiency, then it might be advisable to apply CalMag 🙂

    Happy Growing

  6. believe I do have calcium problem, does the marijuana booster help this problem or do I need some calmag?

  7. A PH of 5.8 is the recommended PH for hydro systems under normal circumstances. I believe Robert was applying an adapted PH level to help counter the Calcium deficiency.

  8. So you recommend that water/nutrient solution should be PH’d to 6.2-6.5 in hydro or coco coir? Seems like I see everybody running 5.8-6.0?