Why You Need Cal/Mag in Coco

Is Cal/Mag supplement really needed?

Why do you have to “buffer” coco?

If you use buffered coco, do you still need Cal/Mag?

If these are your questions, this is your article!

All cannabis fertilizers come with Calcium (Ca) and Magnesium (Mg). However, Ca and Mg deficiencies are the most common problem in Coco grows. The reason for this is the coco itself locks on to Ca and Mg and renders them unavailable to the plant. You can and should buffer the coco with Ca and Mg prior to use. Be sure to see our tutorials, “How to Prepare and Buffer Coco Coir” and “How to Reuse/Recycle Coco Coir”. However, even if you buffer the coco thoroughly, you should still add additional Cal/Mag supplement.

Understanding Cation Exchange

Coco is known as a neutral grow medium, but there actually are cation exchange sites in coco. These sites on the surface of the coco fibers will form bonds with particular nutrient cations. The cation exchange capacity of coco is unlike soil or other grow media. The cation exchange sites in coco naturally come loaded with sodium (Na) and potassium (K) cations. However, the Na and the K are only weakly held to the exchange sites. In the presence of calcium (Ca) or magnesium (Mg), the sites will release their Na or K cations and lock onto the Ca or Mg. Once the cation exchange sites in coco have locked on to Ca or Mg, they are “buffered” and stay remarkably stable.

The cation exchange sites in unbuffered coco can pull nearly all of the Ca and Mg out of a solution. If you try to grow cannabis plants in unbuffered coco, they will experience Ca deficiency. This is tough to correct while plants are growing because Cal/Mag supplements have a strong impact on Electrical conductivity (EC). The total dose that you can provide is limited by EC, even though it all may be going to the coco and none to the plant.

Buffering the coco in advance is a critical step to creating an ideal growing media. However, even in fully and properly buffered coco, you should continue to provide additional Cal/Mag supplement.

Why do you need Cal/Mag Supplement If the Coco is Buffered?

The simple answer is that the coco is constantly breaking down. As large fibers of coco break down in the pots they expose new surface areas of the coco fiber. This also exposes new cation exchange sites that will take Ca and Mg from your nutrient solution and lower the amount available to the plant.

When adding Cal/Mag supplement, you are not adding it for your plants! You are adding it to satisfy the coco. The amount that you need to add reflects the needs of the coco, not the plant. Coco breaks down due to a variety of factors, but you can expect it to need the most Cal/Mag supplement early in the grow. The fresh coco will have the greatest potential to break apart and this is hastened by the roots of young plants. As young plants spend much of the energy pushing their roots through the coco they contribute to breaking it down and create an ongoing need for additional Ca and Mg to be added to the water. Later in the grow, as plants are flowering, the coco will have become more stable and as a result it will need less Cal/Mag supplement. This is helpful, as Bloom Boosters can step in and fill the EC quota that Cal Mag can surrender.

Guidelines for Using Cal/Mag Supplement in Coco

Cal/Mag and EC:

Cal/Mag supplements have a strong impact on EC. As a result, you really don’t want to give more than needed because that will limit the amount of other nutrients that can be provided. If you are confident in your buffer, you may lower the dose to make room for other nutrients, especially late in flowering. However, some Cal/Mag supplement should be given in all nutrient solution.

During Vegetation:Half to Full Dose Cal/Mag:

If you have any doubts about your buffer, or if you see any signs of Ca deficiency you should give a full dose. I use General Hydroponics “CALiMAGic” supplement and the full dose is 5ml/gallon. If you are very confident in your buffer, you may start out with a half dose. If you start out with the full dose, you may cut the dose in half during late vegetative growth or continue the full dose until flowering.

During Flowering: Half to Quarter Dose Cal/Mag:

Cal/Mag supplement should continue to be given but can be reduced to half the dose given during vegetation. However, if the coco was not fully buffered, lowering the dose may lead to Ca or Mg deficiencies, which requires returning to the full dose. If plants show no signs of Ca deficiency, you may reduce the dose to ¼ strength. During the last weeks of flowering I give my plants only 1.25ml/gal of CaliMagic, which is the lowest dose that I recommend.

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Author: Dr Coco

I am a university professor and have taught courses in horticulture. I am coco for cannabis and I hope you are coco for cannabis too :) Grower Love!

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