Calcium Deficiency


Calcium is a micronutrient that is responsible healthy growth, cell wall structure and stress reduction. Also, calcium is essential for early growth while flowering. Calcium in contrast to other micronutrients is considered quite large. This effects its ability to be absorbed at the root level in its naturally derived forms. Popular soil amendments like dolomite, ouster shells can have a pH buffering effect, while gypsum won’t.  

Calcium once taken in through the roots moves relatively slow through the plant (it is a semi-mobile nutrient), which means on absorption it tends to stay put within the plant structure. This can make identifying its deficiency/toxicity easier as signs of issues will coincide with the time that growth happened and its availability within the plant. Signs of a calcium issue will show up on leaves that are actively growing as well as older leaves. 

Calcium Deficiency

First signs of calcium deficiency will be seen in newest growth, with light contact, as deformed margins in the leaf having an appearance of ragged edge look with speckled browning. Also browning necrotic spots will be seen in older leaves and because Calcium is a semi mobile nutrient this damage will not recover.

Calcium Deficiencies can be common when a grower is using reverse osmosis water, often there is enough latent calcium in tap water to suite your plants needs. Also when the pH of your substrate is lower then optimal to absorb it, making chelated nutrients like ProCal or Cal-Mag a highly desirable source. Growing in inert medias like hydro or coco coir or rockwool will require planning as well to insure proper amounts of calcium are readily amiable 

Calcium Is most readily available:

  • 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)

A Calcium Deficiency left unchecked will have a number of adverse effects such as:

  • 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

Calcium Toxicity

A calcium toxicity can sometimes be difficult to diagnose since calcium deficiencies can be misdiagnosed as magnesium, iron, and/or other cannabis deficiencies. And because of the common ways of supplying Calcium to a plant most toxicities will be first seen as lock out of other nutrients.

Flush your media and recharge at proper pH and from their adjust your calcium source. If in soil evaluate if its amendments, to see if a change is needed to either the additionally supplied calcium or too much available calcium exist in the soil requiring a media change.

Sources of Calcium:

Because calcium is needed in such low amounts throughout a plant’s life, finding a source that works with your plants environmental needs is important. There are many quality sources of calcium from liquid products as well as derivative sources like dolomite or bone meal. As a liquid formula matching your formulation needs is about which type of soluble Calcium will carry best with your nutrient program. In soil derived applications knowing your particle size and length of time it takes to break down from its source, bone meal, ouster shells, dolomite etc.… will be key.

When using liquid fertilizers most often calcium is in the form of Calcium Nitrate or Cal-Mag in an effort to increase transpiration of calcium. Using these formulations must be done with care and in proportion to other nutrients, as calcium can have an adverse effect of the uptake of Magnesium and Potassium uptake. 

Solution for Calcium Deficiency in Cannabis

When you have confirmed a Calcium deficiency the best practice is figure out if its rooted in lack of available calcium, pH issues with substrate or competition at the root zone with other nutrients. If you are not in soil flushing your media with appropriately pH’ed water and then adding in a properly pH’ed nutrient mix with adjusted Calcium source should fix your problem.

If you are in soil you simply need to add more calcium to your feed and correct and pH issues in your media. If that requires you to do a flush please note that derivative sources of calcium, like dolomite, gypsum etc..  break down faster based on particle size and you may need to adjust your soil armaments and or add  another source.

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.pastedGraphic.png

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.

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