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Calcium Deficiency

Calcium Deficiency in Cannabis: Identify, Fix, Prevent!

A calcium deficiency in cannabis could have far-reaching effects on your crop. It’s not needed in the quantities of nitrogen, phosphorus, and potassium (the vital NPK combination), but don’t let that fool you. 

Calcium (Ca) is a macronutrient all vegetation requires, and your homegrown cannabis is no different. We examine what you need to look out for and how you can correct a marijuana calcium deficiency. 

The health of your plants and the viability of your harvest depend on early, accurate diagnosis and immediate treatment. So, let’s act fast. 

Signs of calcium deficiency in cannabis plants, roots, or leaves

A scarcity of this element manifests in many ways and affects various plant structures. It’s essential for general well-being and promotes efficient biological processes. It also leads to other common nutrient deficiencies in cannabis

This element is critical for the formation of your plants as it strengthens the cell walls and boosts mitosis. It promotes structural strength from the roots to the leaves and, most importantly, the buds and flowers. 

A shortage prevents constructive potassium absorption, which is essential for flowering. Late-stage calcium deficiency compromises yield and even kills off your herbage. This chemical compound is also needed to ensure the uptake of other necessary nutrients.

Most soil has sufficient natural deposits, but hydroponic set-ups and coco coir options require supplemental action.

cannabis calcium deficiency chart
Lack of calcium in cannabis plants: infographics with all the symptoms

Danger signs include:

  • Brown spots, yellowing or even purple weed leaves
  • Wilting, unhealthy plants
  • Nutrient lock-out due to feebly functioning base
  • Misshapen new growth in the flowering stage with an overall reduction in bud production and quality 
  • Root uptake issues characterized by sogginess or drying colas 


Scientists call it a semi-mobile nutrient, so calcium deficiency marijuana shows complications in the later stages. The fastest sprouts are generally the shoots near the top of the plant, but the middle could exhibit symptoms, too.

You notice young growth slows and may result in weed leaves curling up and down, twisting, and even dying off. Recent shoots often look yellow or purple, and general health declines as plants can’t harvest the necessary nutrients. 

deformed weed leaves (Ca deficiency)
New seedlings are deforming due to the lack of calcium, their leaves are curling down

The plants wilt in extreme heat as this macronutrient aids in the survival of unusual environmental stress. It also strengthens cell walls, so a lack of Ca results in weak branches that break easily. They can become hollow and may even start to rot from the inside. 

A calcium deficiency during flowering causes the most significant damage because it impacts bud production. The calyx is the foundation for virgin bloom, but these form incorrectly when levels are too low.

New calyxes have distortions or crinkles and never manage to fill out. These abnormalities signal a drastically reduced harvest if your plants even survive until then.


Calcium is critical for successful germination and root production in the early stages of the plant’s lifecycle. It impacts how marijuana reacts to environmental conditions like extreme heat.

The health of your roots determines how well the plants take up nutrients. Vitamins should be available from the soil or hydroponic solution. Cannabis calcium deficiencies interfere with the process, causing other hassles like a cannabis manganese deficiency.

When the roots are affected, they often appear underdeveloped and weak and may be short and brown. In extreme cases, they die and fall off. 

image of brown slimy cannabis roots - calcium deficiency in hydroponics
Brown slimy cannabis roots – calcium deficiency in hydro

Fundamental plant health is at stake, and conditions like slimy root rot could occur. This bacterial infection can kill your greenery if you don’t correct the issue. 


Indications of a marijuana calcium deficiency often show in the leaves of your cannabis crop. The green color can darken, and pictures clearly show brown spots, which are the most definitive sign of scarcity. The first clue is often yellow tips. 

yellow and brown tips of cannabis leaves
An early stage of calcium deficiency: yellow spots on weed leaves and brown tips
early stage of calcium deficiency in cannabis
An early stage of calcium deficiency: weed leaves are curling up with yellow spots on them

Proper protein and vitamin synthesis, transpiration, and effective operation of root hairs and leaf stomata rely on usable Ca levels. Brown spotting on weed leaves is a dead giveaway that your crop is suffering a nutrient famine.

Ca deficit on cannabis
Small yellow spots on the leaves
calcium deficiency: dark spots
You also may notice small dark spots on cannabis leaves that can be a symptom of calcium deficiency
Ca deficit in cannabis
Example of brown and yellow leaf affected by calcium deficiency

Blotchy mottling and necrotic spotting are often a precursor to leaves dying off. Recent shoots display small, distorted fronds that may also curl up and crinkle. Growers often note weed leaves clawing, too.

a middle stage of calcium deficiency
A middle stage of calcium deficiency: brown spots are progressing

The brown spots on marijuana leaves are usually seen in those receiving light and nearest the top of the canopy. 

When does calcium deficiency appear?

A calcium deficiency in weed plants may lead to devastating crop issues. Why do these shortages occur, and what can you do to avoid them? Most modern commercial soil mixes contain a full spectrum of nutrients meaning potential inadequacies are unlikely.

Growers can avoid problems by starting with high-quality soil or adding compost. Most ground mixes have decent reserves to sustain plants throughout their life cycles. 

We list the most common triggers below: 

  • Acidic soil: Growers are less likely to suffer a marijuana calcium deficiency if they cultivate with outdoor cannabis seeds. Acidic foundational dirt increases the potential for symptoms outside. 

Pine forests thrive in these substrates, but cannabis suffers severe symptoms with low pH for weed plants in soil

  • Hydroponic set-ups: Most outdoor ground mediums have sufficient reserves to satiate marijuana plants, but hydroponic systems are different. 

As the roots rest in the water, you should manually introduce nutrients. Hydro set-ups require regular checks to test pH.

  • Water: Many growers depend on water to satisfy their calcium requirements. Mineral water provides a decent source, but be aware that the purification process removes about 89% of the soluble element. 

Filtered water (like reverse osmosis and distilled versions) contains trace amounts unlikely to solve a scarcity. Tap water varies and depends on the region. 

  • LED lighting: Light-emitting diodes (LEDs) save power and money, but the spectrum is more limited—not always the best light for growing weed. The wavelengths to control the production of this chemical compound are challenging to achieve with LEDs. 

If you’re cultivating with these lights, watch out for a purple coloration that may signify calcium deficiency weed. Switching to a UVA system for a while may raise Ca production. 

  • Coco coir substrates: This natural organic medium is excellent for aeration, drainage, water retention, minimizing pests, and maintaining nutrients. 

It has a natural pH, but you need to feed your plants as coco contains minimal quantities of growth nutrients. While most growers know of the NPK balance, Ca is vital to the health of your crop.

  • Too much potassium: An excess of this vital element mimics a calcium deficiency in cannabis. A surplus of manganese has the same effect.
  • pH too low: If the growing medium pH is below 6.2, this crucial element can be locked out even if reserves are present. A pH of 6.2–7 is optimal.

Shortages manifest in different ways on separate lineages. Sometimes plants from the same strain and in the exact environment need different amounts. It’s essential to monitor your flora regularly to know what they require. Don’t overdo your input of the nutrient, either.

How to fix calcium deficiency in marijuana plants

If you’re cultivating a homegrown crop, it’s imperative to know how to fix a calcium deficiency in weed plants. Introducing sources into your growing medium counters low pH and eliminates brown spots on cannabis leaves.

Commercial fixes

Dolomite powder is a limestone compound that adds Ca and magnesium (CalMag) and raises pH, combating acidity. It provides more nutrients than garden lime, and growers usually use it in conjunction with other fertilizers.

Commercial CalMag solutions are widely available and rapidly balance shortages by elevating pH. Calcium acetate or CalMag acetate also improves levels and rectifies the problem.

Plants need both elements, and a cannabis magnesium deficiency can often accompany low Ca levels. 

Sort out a marijuana calcium deficiency by using liquid Ca or liquid lime supplements. Some use dehydrated lime dissolved in water to change the pH of their soil. Others use fish meal, but powdered bones also work well. 

DIY fixes

Save money by making nutrient or foliar sprays. Seaweed is a fantastic nitrogen, bromine, iodine, sodium, and calcium source. Use it to tackle a cannabis iron deficiency.

Another suitable provider of Ca is eggshells. Boil eggs in water and save the infused H20 for treating a weed calcium deficiency. Allow the shells to dissolve in water and add it to your substrate. The liquid is rich in nitrogen, phosphorus, collagen, and magnesium, which aid health and growth. 

Chamomile contains Ca and potash and is excellent for addressing problems that manifest with stunted growth, also called damping off. You could even use chamomile tea which also eradicates many fungal issues.

Antitranspirants are made from natural oils and can rectify a calcium deficiency in weed. Mix with skimmed or powdered milk. Buy them at most gardening centers.

Compost enriches your soil with a multitude of marijuana nutrients. Experts swear by compost tea, which blends mulched weeds and herbs with water. Soak, strain, and dilute before spraying on your crops to correct a lack of calcium.

Always test homemade concoctions on a portion of your crop first to ensure they aren’t too potent or toxic. 

Cannabis calcium deficiency kills 

Now you know what to look for if telltale indicators of a calcium shortage crop up. The problems growers face show most obviously in brown spots on the leaves, but watch the roots and overall plant health, too. 

Acidic soil is the most likely culprit, but hydro cultivators also face this threat and must treat their medium to avoid costly outcomes. Filtered water and LEDs can lead to scarcities, and if not attended to promptly, they are potentially fatal. 

Commercial and DIY fixes are available to growers who want to be proactive in containing their cannabis calcium deficiency. Avoid issues by investing in pest-resistant strains or buying high-quality marijuana seeds. Superior genetics protect your plants.

The i49 Seed Bank has the broadest range of top-end cannabis seeds available in the USA. We deliver discreetly, right to your door in mere days. 

AUTHORED BY: Douglas Kester Mr. Kester came to i49 with a wealth of experience. He’s worked in the cannabis industry for more than ten years. As a growing expert at i49, Douglas finds it hard to choose a favorite strain. Instead, he regards each one as unique and full of potential. Douglas finds it rewarding to experiment with specific cultivars and cross-breed to discover a new one. He strongly believes in sharing the benefits of marijuana with as many people as possible to avoid any misconceptions about the herb. Mr. Kester creatively produces information based on what he’s learned and his experience obtained by implementing what he knows. i49 is proud to have Douglas as part of the team.

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