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PH & Magnesium Deficiency

By St0ney & OzGrowa

It has come to my attention that some advice I was giving out was incorrect. In particular, my advice about Magnesium Deficiency and Epsom Salt. When I first started growing I was told (at another site that will remain nameless ) that Marijuana had very high needs for Magnesium and most hydro nutrients didn't have enough. So adding Epsom Salt was the trick to keeping Magnesium Deficiency away. So for every grow since then I’ve used Epsom salt, and I have advised others to do the same.

Well, The other day OzGrowa informs me that, that is incorrect. Well, I was shocked to say the least. He informed me that a low PH usually 'locks out' Magnesium and most hydroponic nutrients have plenty of it.... And some have too much.

So, being the computer geek that I am.. I immediately started researching this and found him to be quite correct.

Here is the truth about Magnesium Deficiency

First let's start off defining a few terms.

Magnesium (Mg)- is essential to photosynthesis in plants. It’s the "main molecule" in chlorophyll, the green coloring in green plants! Photosynthesis is the process by which plants use the sun’s energy to create carbohydrates. Without magnesium, plant leaves turn yellow (usually at the bottom) and will soon die.

pH- is measured on a scale of 1-14 with 7 being "neutral". Acids are lower than 7 and alkalis (bases) are above 7. To be technical, the term pH refers to the potential hydrogen-hydroxyl ion content of a solution. Solutions ionize into positive and negative ions. If the solution has more hydrogen (positive) ions than hydroxyl (negative) ions then it is an acid (1-6.9 on the pH scale). Conversely if the solution has more hydroxyl ions than hydrogen it is alkaline (or base), with a range of 7.1-14 on the pH scale.

Pure water has a balance of hydrogen (H+) and hydroxyl (OH-) ions and is therefore pH neutral (pH 7). When the water is less than pure it can have a pH either higher or lower than 7.

Why should you care about any of this?

When the pH is not at the proper level marijuana will lose it's ability to absorb some of the essential elements required for healthy growth. For all plants there is a particular pH level that will produce optimum results. Marijuana likes it's hydroponic solution to be 5.5 to 6.1 and soil to be 6.3 to 6.8. Although most plants can still survive in an environment with a pH of 5.0 to 7.5.

If the pH is too high, marijuana suffers from a lack of iron, zinc, manganese, copper and boron. If the pH is too low, it lacks phosphoric acid, calcium, and magnesium. At lower pH (more acidic) ranges, diseases can thrive. Normally, plants tend to take up more acidic elements, causing pH levels to increase or drift up the scale.

Now, from my understanding of this is, you should let your hydroponic solutions 'drift' up to 5.9 to 6.0 for hydroponic systems and for dirt grows let it drift up from 6.3 to 6.8 to allow the Magnesium to be available without the addition of Epsom salt (which results in EDTA lockouts because we are adding too much Magnesium.)

Also Oz had this to add:

Id also say that the whole system of nutrients is a delicate balance of +ve and -ve ions, adding a certain element such as Mg usually has the effect of altering the potential with a sudden and drastic availability of the element within solution, the plant uptakes this solution and the problem is further compounded as the plant goes further away from center...I have read so many growers say "wow the plants have gone really green after I added the Epsom Salts" (excess Mg symptoms) then a few days later its "my plant has stopped growing and is starting to yellow in the leaves" (Iron lockout).... as a further example or approach to the overall picture of nutrient solutions think of pH correction....adding ph up (+ve ions) to a solution that you have added too much down ie acid (-ve) to, it shouldnt be done, the whole solution should be dicarded. As it is in DWC, NFT, Dripper,etc etc in hydroponics, if we discard and completly replace our solutions regularly (and use a hydroponics nutrient to begin with) deficiencies will become non existant. Occasionally, and I mean occasionally, we will need to add a slight amount of Mg, and it should be fractional, but this should be such a rare situation if the other practises are correct.

PH drift is a great thing, letting it climb to 5.9- 6.1 (or 6.5-6.8 for soil) isnt going to have an adverse effect whatsoever, in fact the inverse is true, the rise will permit correct iron, potassium and phosphorous uptake and prevent the deficiencies that people claim to be experiencing. This is especially the case during flowering, the PH rise will result in slightly more P being absorbed so the constant battle to keep the PH at 5.5 or even lower I think is a little futile.

-Oz-

Here is a look at what Magnesium Deficiency does to a sugarbeet plant.

 

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