Coco, P, and calcium/magnesium

Grat3fulh3ad said:

The target numbers I shoot for are 100 - 100 - 200 - 60 for N-P-K-Mg, normally... but for the coco I think the lower P and K are needed...
Also, although a wide range of ratios in the K-Ca-Mg relationship will provide optimum growth, it is generally accepted that there should be a bit more K than Ca, and a bit more Ca than Mg... This was why I chose epsom over cal-mag...

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WolfieCat said:

I hope that helps

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Grat3fulh3ad said:

Originally Posted by Grat3fulh3ad View Post
The target numbers I shoot for are 100 - 100 - 200 - 60 for N-P-K-Mg, normally... but for the coco I think the lower P and K are needed...
Also, although a wide range of ratios in the K-Ca-Mg relationship will provide optimum growth, it is generally accepted that there should be a bit more K than Ca, and a bit more Ca than Mg... This was why I chose epsom over cal-mag...

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stoned40yrs said:

Here's a good old post from this forum:

Coco colloids may store huge amount of cations, but the main thing to understand when managing feeding/ph management is that they are uptaked at very different speeds, and uptake speed determined the best balance between how much cations of each element are stored.

B and Ca cations are uptaked very slow, while Mg and most micros are uptaked at medium speed and K are absorbed very fast. Couple that with the requeriments of each element and you get the best balance of cations stored in the coco, wich is aprox 60-65% Ca, 25-30% Mg, 5% K and about 1% of micros.

Ph affect the speed of uptake of the different elements. Still being more than required of some element stored in the coco, an inadecuate ph may lead to a deff of that element because at the uptake speed at a given ph, it may be too little coco colloids occupied by that element cations to provide enough uptake.

So feeding profile must be well matched with ph used. There are many possible ways of achieving sucessfully grows in coco by varying nute profile and ph used.

On the ph most used when growing in coco, 5.3-6.3 (adviced by most coco nutes manufacturers) hydroponically (thats very different with organic nutes, as then more than ph what affect nutes avalaibility is the descomposition rate of them by benefical microorganisms), aprox over 5.8 there is faster uptake of Mg than of Ca, leading to a Ca accumulating in the media, and below 5.8, more Ca uptake than of Mg. If the feeding profile dont compensate this, finally the cations balance in the coco is compromised and there is a lock out. Its commonly called "excess salt in the medium" or "salts build up", but is more correct calling it an unbalancing, because is one element wich accumulates for other element wich become not enough present.

K uptake is rarely affected due is very fast absortion, and often K deff only shows when there had been a previous deff solved by adding salts to fix it, resulting in almost no free coco colloids avalaible to K cations being bonded. Typical of having a Mg deff because thare has been an accumulation of Ca for a disminution of Mg and instead of treating it lowering ph to increase uptake of Ca and restore the cations balance, its fixed by adding Epsom salts, wich increase Mg avalaible at the cost of reducing K avalaibility. Finally both are reduced if ph continues high and the nute profile (Ca/Mg/K percentage ratio) remains unchanged.

This is due Ca is a very strong bivalent cation, while Mg is bivalent too but with weaker electric charge (affinity for negativelly charged coco colloids) and K and Na are one valent cations wich are easily displaced by the two previous.

Resuming: keeping Mg and Ca balanced in the coco, both by nute profile and ph management is the key to grow in coco with the best results.

Peace,
knna

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Dr.RedWhite said:

If I got this straight Coco coir has a lot of K in it and this causes lockout problems with calcium and magnesium. At least until some imbalance is overcome? Or PH is brought down to 5.8? Can someone give me the right info on this please?

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