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Calcium Deficiency


by Nebula Haze & Sirius Fourside

This marijuana leaf is showing signs of a calcium deficiencyProblem: Calcium is an important nutrient which helps provide structure to the cannabis plant and helps it withstand stress like from heat.

A cannabis calcium deficiency can sometimes be difficult to diagnose since calcium deficiencies are often accompanied by magnesium, iron, and/or other deficiencies.

Calcium moves relatively slowly through the plant (it is a semi-mobile nutrient), and tends to remain concentrated in older growth. Calcium deficiencies tend to show up in newer growth (upper leaves).

Picture of a calcium deficiency on a cannabis leaf - white background so you can clearly see the brown spots - calcium deficiencies appear on the upper leaves (new growth)

Calcium Deficiencies Appear Near Top of Plant

Calcium deficiencies tend to appear on newer growth, which means it first appears on the leaves towards the top of the plant.

Some of the most noticeable signs of a calcium deficiency will appear on new, upper leaves which may display:

  • Dead spots
  • Crinkling
  • Spotting / Mottling
  • Small brown spots
  • Stunted growth
  • Small or distorted new leaves
  • Curled tips
  • Leaf die-off
  • Affected leaves may appear dark green

Here's a close-up of a calcium deficiency that appeared on leaves towards the top of a cannabis plant grown in coco coir:

Marijuana Calcium Deficiency - Closeup of brown spots which first appear on young (upper) leaves

Other Symptoms of Calcium Deficiency

If a cannabis plant is affected by a calcium deficiency for too long, it may begin to show the following symptoms due to the lack of calcium.

  • Stems become weak or flimsy and may crack easily
  • Stems become hollow or show inner signs of decay
  • Plant does not stand up well to heat
  • Flowers/buds do not develop fully, or development is slow
  • Roots appear weak or under-developed
  • In severe calcium deficiencies, parts of roots may even die off or turn brown
  • Roots are more susceptible to root problems like slimy root rot

Cannabis tends to like high levels of calcium, so it is unusual to feed too much calcium when using normal amounts of nutrients and/or regular soil. There are not many known cases of cannabis calcium toxicity (too much calcium), however too much calcium can cause the plant to lock out other nutrients, so it's important not to go overboard..

Calcium deficiencies are more likely to appear when...

  • Grower is using filtered or reverse osmisis (RO) water to feed plants - the amount of calcium found in tap water varies, but some tap water has enough calcium to prevent calcium deficiencies
  • Growing cannabis in hydroponics with nutrients that don't supplement calcium or when growing in water that has less than 6.2 pH
  • Growing cannabis in coco coir that hasn't been supplemented with calcium or below 6.2 pH
  • When growing in soil or soilless growing medium that hasn't been supplemented with calcium (usually from dolomite lime) or is acidic (below 6.2 pH)
  • Too much potassium can also sometimes cause the appearance of a calcium deficiency
  • Outdoors - calcium deficiency is more likely to appear in acidic soil (below 6.2 pH)

Cannabis Calcium Deficiency - Brown spots on young (upper) leaves

Different strains of cannabis tend to have different nutrient problems. Some cannabis strains (or even specific plants) tend to use much higher levels of calcium than others, and so you may see calcium deficiency problems with one plant even when all the other plants (which are getting the same nutrients and environment) aren't showing any signs of deficiency.

 

Solution For Calcium Deficiency in Cannabis

Your cannabis plant may show signs of a calcium deficiency if the pH at the roots is too high or too low. That is  because when the pH of your root zone is off, your cannabis cannot properly absorb calcium through its roots. Therefore the first step is to ensure that you have the correct pH for your growth medium. Learn more about pH and cannabis.

Please note: After a calcium deficiency is cleared up, the problem (brown spots and unhealthy new leaves) will stop appearing on new growth, usually within a week. Please note that leaves which have been damaged by a calcium deficiency will probably not recover or turn green, so you want to pay attention to new growth for signs of recovery.

  • In soil, calcium is best absorbed by the roots in the 6.2 - 7.0 pH range (in soil, it's generally recommended to keep the pH between 6.0 - 7.0, but calcium specifically tends to be best absorbed above 6.2)
     
  • In hydro, calcium is best absorbed by the roots in the 6.2 - 6.5 pH range (in hydro, it's generally recommended to keep the pH between 5.5 - 6.5, but calcium specifically tends to be best absorbed above 6.2)
     

If you suspect your growing cannabis plant has a calcium deficiency, flush your system with clean, pH'd water that contains a regular dose of cannabis-friendly nutrients that includes calcium. This will remove any nutrient salts that may be affected the uptake of calcium and help restore pH to the proper levels..

To supplement with extra Calcium... (it's very rare to give a cannabis plant too much calcium, however, too much calcium can lock out other nutrients so don't go overboard)

Calcium, magnesium, and iron deficiencies often appear together in cannabis. Many growers decide to purchase some sort of Calcium-Magnesium (often called Cal-Mag) supplement for their grow room in case this common deficiency appears.

Listed below are common cannabis Calcium supplements, along below with some general information about each one. After supplementing with Cal-Mag and correcting the pH, you should expect to see new healthy growth within a week. Remember, the old leaves will probably not recover, but new growth should be green and healthy.

Cal-Mag is Well Suited For Hydro, Coco Coir, or Soil

Botanicare Cal-Mag Plus is a calcium, magnesium, and iron plant nutrient supplement. General application is to mix 1 tsp (5ml) of Cal-Mag into each gallon of water. I have used Cal-Mag Plus several times with great results.

Guaranteed Analysis: Nitrogen (N) 2.0%, Calcium (Ca) 3.2%, Magnesium (Mg) 1.2%, Iron (Fe) 0.1%

Derived from: Calcium Nitrate, Magnesium Nitrate, Iron EDTA
 


 

Dolomite Lime - For Soil Growers (Organic)

If you're looking for a way to supplement calcium in your organic or soil setup, I highly recommend a product called "Dolomite Lime."

Dolomite is a good source of calcium and magnesium and can be mixed with your soil. The great thing about dolomite is it works slowly over the course of a few months.

Dolomite has a neutral pH of about 7.0 and will help keep soil at the correct neutral pH range which is optimum for cannabis growth.

You can buy Dolomite Lime online, but with shipping it's almost always waaaay cheaper to pick up a bag at a home improvement or gardening store such as Lowes, Home Depot, gardening centers, etc.  If possible, try to get a finer grade of dolomite compared to something that is more coarse.

How to Use Dolomite Lime for Cannabis: When growing cannabis indoors, add 6-7 teaspoons of fine dolomite lime to each gallon's worth of soil. So if you're mixing enough soil to fill a 5 gallon container, you want to add 30-35 teaspoons (about 2/3 cup) of dolomite lime to the mix. Mix the dolomite lime and the dry soil thoroughly, then lightly water it with water that has been pH'ed to 6.5. After getting the soil wet, mix the soil well and wait a day or two to let the soil settle before checking the pH and adding plants. When growing in an outdoor garden, follow the dolomite lime manufacturers instructions.

If you cannot get rid of your calcium deficiency, please consult our 6-Step Cure to 99% of Cannabis Growing Problems

Picture: 
Cannabis Calcium Deficiency - GrowWeedEasy.com
Big Symptom Picture: 
Leaf Color: 
Brown or Dark Spots
Mottling / Mosaic Pattern
Leaf Symptoms: 
Upper Leaves / Newer Growth Affected
Leaf Edges Appear Burnt
Leaf Tips Appear Burnt
Leaf Tips Die
Spots
Mottling / Mosaic
Slow Growth
Twisted Growth
Abnormal Growth
Plant Symptoms: 
Weak Stems
Slow Growth
Twisted Growth
Root Symptoms: 
Brown
Slow Growing
Other Symptoms: 
Buds Not Fattening