Many growers are really preoccupied with pH of their soil or water tank, but they rarely know what pH really is, except that it can be acidic, neutral or alkaline. Well, it can be due to concentration of hydrogen ions, which is the very basis of pH.
In chemistry pH is defined with this equation:
pH = -log10[H+]
This breaks down to POTENTIAL OF HYDROGEN (one the left side) equals (in the middle) negative base 10 logarithm of the molar (or units of moles per liter solution) concentration of hydrogen ions (on the right side).
This equation was coined in 1909 by by Danish biochemist Søren Peter Lauritz Sørensen, and it measures the acidity or basicity of the solution on the logarithmic scale (nonlinear scale used when there is a large range of quantities), that spans from 0 to 14, where each single unit corresponds to a ten-fold change in hydrogen ion concentration.
To be clear, solutions over 7.0 are considered alkaline, and solution below are considered acidic with those that are exactly 7.0 considered neutral.
The interesting is, that pH scale is theoretically open-ended, but it's been SIMPLIFIED for the clarity as an extremely acidic solution can have 100,000,000,000,000 times more hydrogen ions than a very alkaline one, and vice versa... a strongly alkaline solution can have 100,000,000,000,000 times more hydroxide ions than an acidic one.... which comes down to very advanced maths, that might cause a severe headache if you're not trained for it!
On the top of that the concentration of both ions in soil or water is shifting all the time, so there's no way to get a fixed number for more than a few seconds!
Let's break it down
According to the above-mentioned, pH is all about the concentration of hydrogen ions (H+). But where do they exactly come from? Well, they come mostly from water (H2O), which splits up in natural conditions into hydroxide (OH-) and hydrogen (H+), which quickly forms so called hydronium (H3O+), commonly referred to as hydrogen though.
This basically means that in order for the solution to have pH of 7.0 there has to be an equal number of of hydrogen and hydroxide ions. If the number of hydrogen ions go up, then the solution becomes acidic. And when the number of hydrogen ions go down, then the solution becomes alkaline.
But soil has much more going on that just catching hydrogen ions from water (mostly rainwater). In fact soil pH in nature is mostly regulated by decomposition and mineralisation of organic matter as well as its geological structure (strata of calcium, magnesium, aluminium, sodium or iron), and root respiration of plants growing in it.
Adjusting pH for cannabis
This is easier said than done. Adjusting pH in hydro solution is for example quite easy, which is why hydro growers rely on pH ups and downs all the time to control the absorption of nutrients. However, in soil it's much trickier as soil pH is regulated by another factor called BUFFERING CAPACITY.
What it basically means is, how much of acid or alkaline solution a given soil can soak up before its pH starts to shift. If buffering capacity is high, then changing it becomes a real challenge, and if it's low, then it's much easier.
As a rule of thumb, high clay and humus (peat belongs here too) content will up buffering capacity of soil significantly making a forced pH swing quite difficult!
In organic soils it's almost impossible to change it permanently as soil microorganisms will always fight to keep it in the optimal range to thrive, but even in soilless mixes a desired value may be quite hard to set for longer than a couple of hours due to hydrogen exchange.
In fact, during cannabis' life regulating it with acidic or alkaline solutions is pretty much pointless - unless you want to kill your plant to prove a point - as it'll always bounce back, and the only way to set it in desired parameters is to correct the soil before planting and test it for base saturation (the test has to measure hydrogen saturation).
Moreover, measuring runoff to figure out pH is a VERY WRONG way to do it as percolating water won't reflect THE ACTUAL pH OF SOIL, but only its own pH after passing through the medium, and the only way to get a more or less accurate reading is THE SLURRY TEST!
Photo credits: 1st from the top is Gorilla Glue grown organically indoor by Ilikemsticky, 2nd from the top is Tangie grown in #highbrix soil by Doc Bud. Both pics courtesy of 420Magazine. Tables credited directly
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