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Calcium Deficiency in Weed plant

How to Fix Calcium Deficiency In Weed Plants

November 19, 2021
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Cultivating cannabis is a rewarding endeavor that helps many growers relax and get in touch with nature. Overcoming challenges like crop diseases, pathogens, and calcium deficiency in your weed is a necessary part of the journey.

Calcium is a vital nutrient for healthy marijuana plants. It plays several key roles in the plant's development, and a shortage can be devastating to your crop’s health and final yield.

Below we take a close look at the roles of this mineral in cannabis development. We also highlight the symptoms of a nutrient shortage and provide guidelines on how to fix a calcium deficiency in plants. Let's kick things off by defining the issue in detail.

Weed plant calcium deficiency
Weed plant with calcium deficiency

What is calcium deficiency?

A cannabis calcium deficiency refers to a situation where the crops aren't getting enough of this particular nutrient. There are several reasons for this issue to crop up, but when the levels of calcium decline, there's usually excess manganese in your soil. 

A calcium deficiency in weed plants occurs more frequently in substrates with higher acidity. A shortage of this nutrient leads to issues like:

  • Organic matter at the root zone isn't decomposed optimally.
  • Nutrients aren't absorbed properly.
  • Nutrient lockout can occur if left too long.
  • Flowering phase slows down.
  • Crops start wilting.
  • Plants become less resilient to common diseases.

What does calcium do for plants?

Marijuana calcium deficiency is a serious problem for growers because this nutrient plays several important roles in crop development:

  • Facilitates nutrient absorption.
  • Assists with germination and root development.
  • Ensures the vitality of the plant cells.
  • It holds the cell walls (New growths rely on this).
  • Helps with transpiration.
  • Ensures the health of hair roots and stomata.
  • Helps with flower development.
  • Assists the plant with heat resistance.
  • Activates enzymes.

What causes cannabis calcium deficiency?

There are several causes for calcium deficiency in weed crops. The main ones are:

  • Low pH
  • Not enough nutrients in the medium
  • Too much potassium
  • Excessive manganese
  • Using reverse osmosis water
  • The strain is susceptible to nutrient deficiencies

Low pH

When the soil pH is too low, calcium isn't absorbed properly through the roots. It can even get locked out completely, causing a calcium deficiency in the weed crops.

Insufficient nutrients

If there aren't enough nutrients for cannabis present in your chosen growing medium, a calcium deficiency is inevitable. Plants can't absorb what isn't there, so you'll need to supplement these crops liberally to avoid the issue.

If you're cultivating your cannabis seeds in coco coir or with hydroponics, you need to add calcium and other nutrients for your crops to develop well. The deficiency is more likely to occur in these substrates, but it can happen in soil too.

Too much potassium

Potassium is another nutrient that's vital to the health of your crops, but too much can lead to a calcium deficiency in marijuana. This mineral impacts how effective the soil is at absorbing calcium, nitrogen, and other vital elements.

Excess manganese

Manganese and calcium need to be balanced. Too much of one can result in a lack of the other.

Reverse osmosis water

Some growers opt to hydrate their crops with reverse osmosis water. The process removes sediment and other particles before giving them to the plant. It also removes certain nutrients, resulting in a marijuana calcium deficiency.

Strain-specific issues

Some strains are more resilient than others. Certain cultivars require more supplementation and stricter feeding schedules, while others can resist the most common cannabis problems.

Be sure to thoroughly research your chosen strain and take precautions to avoid a potential calcium deficiency in your marijuana.

Marijuana calcium deficiency
Marijuana calcium deficiency

Signs of calcium deficiency in weed plants

It's important to try to detect a calcium deficiency in cannabis early. The sooner you establish there's a shortage of nutrients, the more likely you are to save your crops. Fortunately, your plants display multiple symptoms, so you'll be able to act swiftly. Some of these signs include:

  • Discoloration on parts of the leaves
  • Necrosis
  • New growths are unhealthy
  • Roots are weaker
  • Plants become brittle
  • Poor flower development
  • Curled tips
  • Stunted growth
  • Dying leaves
  • Hollow, weak stems


When you have a calcium deficiency in your weed plants, you'll notice yellow spots on some of the foliage (Learn here how to differentiate leaf septoria from calcium deficiency). The leaf edges start losing their vibrancy and begin to fade. You can usually notice the change in new growth and the parts of the leaves exposed to light.


If you don't take action fast enough, a calcium deficiency in your weed plants can become catastrophic. The discoloration often becomes necrotic, with brown spots or dark leaf edges. It can spread to the other parts of the leaves until it dies and falls off.

Unhealthy new growth

Cannabis calcium deficiency can greatly affect the plant’s ability to grow. Its molecular strength becomes compromised, slowing down the development of crops. Stems will also turn a purple color.

Weak roots

A marijuana calcium deficiency often causes the roots to become weak and lose vigor. Without the right amount of nutrients, they become susceptible to rot.

If the problem persists, the roots start to turn brown and eventually die.

Brittle crops

A lack of adequate nutrients weakens the plant's structure. Weak cells will result in brittle, easily breakable stems and branches.

Poor flower development

If your crops don't get enough calcium, the flowers develop poorly. A lack of essential nutrients can result in buds that:

  • Aren't vibrate in color
  • Don’t fill out or become dense
  • Have fewer trichomes
  • Have under developed calyxes

Curled tips

Plants that experience a nutrient shortage sometimes curl at the edges. In the case of a calcium deficiency in marijuana, this typically occurs on the newer sections of your plant.

Stunted growth

Marijuana crops don't grow to their full potential when they lack certain elements. The shortage of calcium stunts the plant’s overall growth; this ultimately affects the size of its yield and bud potency.

Hollow stems

A severe calcium deficiency in your weed plants can cause weak stems. Crops that fall into this category are often flimsy and show signs of decay. They become susceptible to heat stress and lose their resilience.

Calcium Deficiency in Weed plant
Calcium deficiency in weed plant

How to fix calcium deficiency in marijuana plants

You might be wondering how to fix a calcium deficiency in your weed plants. There are a few methods you can employ. These include:

Dolomite lime

Dolomite lime works slowly over a few months. It's an easy way to fix a calcium deficiency in cannabis. You need to mix it with the soil, adding approximately six teaspoons to each gallon of the medium.

Dolomite lime has a neutral pH of 7.0 and helps keep the soil levels ideal for cannabis cultivation. The texture of different brands varies, so opt for a finer option to resolve a calcium deficiency in weed faster.


You can buy various nutrient supplements for plants. Calcium is usually available in products with magnesium. The balanced ratio is beneficial as a shortage of one nutrient is usually accompanied by a lack of another.

If you choose this method to fix your marijuana calcium deficiency, be sure not to overfeed as it can result in levels becoming toxic.

Correcting the pH

If you ask growers how to fix a calcium deficiency in plants, they'll usually advise you to flush the crop. You need to use a solution of water with a neutral pH and cannabis nutrients to correct the levels in your substrate.

                              Symptom                    Correction Method
DiscolorationUse dolomite lime or mild supplement
NecrosisFlush the cannabis to correct the pHOnce new growth stops showing symptoms, maintain the crop with a cal-mag supplement.
Unhealthy new growthDolomite lime in soilCalcium supplementsIf the problem persists, flush to correct the pH
Weak rootsDolomite limeCalcium supplements(Exercise caution when flushing weak roots, as root rot can occur easily when the plant is in this state. It’s best to avoid this option if possible.)
Brittle structureDolomite limeCalcium-magnesium supplements
Poor flower developmentFlushing
Curled tipsCalcium supplements
Stunted growthFlushingCalcium supplements
Dying leavesFlushingDolomite lime
Hollow stemsFlushingDolomite limeCalcium supplements

What is calcium toxicity in cannabis?

Cannabis calcium toxicity occurs when there's too much of this nutrient in the soil. While it's vital for the plant's development, excess nutrients cause a disturbance in the ion balance and harm your crops.

Toxicity can result in leaf burn and can lock out other essential nutrients like potassium and magnesium.

How to treat cannabis calcium toxicity?

If your plants suffer from cannabis calcium toxicity, you'll need to flush your growing medium. Using pure water can worsen the issue, so opt for a softer version. 

A great technique you can utilize is blending a low dose of nutrients with water to flush your crops. This process allows the excess water to wash away but leaves adequate quantities of that particular mineral in your growing medium.

Cannabis Calcium Deficiency
Cannabis calcium deficiency

Nutrient in a nutshell

Marijuana plants need many different minerals to thrive, and calcium is one of its vital macronutrients. If you have a calcium deficiency in your weed plants, you'll notice various symptoms.

The faster you act to rectify the issue, the better your chances of restoring your crop's health. The three methods for fixing a deficiency are flushing, using dolomite lime, and adding supplements. Each of these works to restore the natural balance in your substrate.

If you choose to add supplements, don't overdo it as you could cause cannabis calcium toxicity which is also detrimental and locks out other essential nutrients.

Now that you understand more about the role calcium plays in cannabis cultivation, why not start your own? Check out the Homegrown Cannabis Co. for quality weed seeds and begin growing potent marijuana from home.

About the Author: Kyle Kushman

Kyle Kushman is a legend in the cannabis community. He is the modern-day polymath of pot: cultivator, breeder, activist, writer, and educator. After winning no less than 13 Cannabis Cups, there’s nothing this guy doesn’t know about indoor growing - he’s been there, done it, and is still doing it to this day!

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