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Cultivation Clinic: The Importance Of pH

Nico Escondido

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Sound smart with your friends about the effects of pH on medium and nutes.

The “Power” of Hydrogen

When discussing pH, it is important to first understand what pH is exactly. And while there is much debate over the literal translation of the acronym—some refer to it as “possible” or “potential” hydrogen, while others suggest its meaning comes from the German word potenz, or the “power” of hydrogen—one thing is certain; it’s all about hydrogen.

But why is hydrogen so important?

To start, hydrogen (H) is a chemical element that appears on the periodic table of elements with an atomic number of one (1), meaning that it has only one proton in its nucleus. This is important because it allows hydrogen to take on two forms; either that of an anion, a negatively charged atom (also known as a hydride), or a cation, a positively charged atom. It’s these roles that make hydrogen particularly instrumental in acid-base reactions, which are the basis for nutrient uptake by our plants’ root systems.

When we feed our gardens with nutrient solutions, there are specialized protein and enzyme molecules in the plants’ roots that are structured in specific ways to catalyze chemical reactions using the positive and negative charges of hydrogen molecules. These charges are used to match up with those of other minerals being fed to plants and is known as CEC, or cation exchange capacity.

It is this “match up” of positive and negative charges on a molecular level that allows for roots to absorb nutrients and draw them up into the plants above.

A pH scale measures hydrogen ions. Most cannabis strains prefer a pH level of around 6.5.

Taking pH measurements of your medium, nutrient solutions and waste run-off are all very important to ensuring proper nutrition and development for your plants.

The acidity or basicity of these aspects is really just a measurement of their hydrogen ions.

For ease of reference, these values are converted into a numbered scale that ranges between zero and 14, with seven being neutral (or pure water). Numbers over seven up to 14 are considered basic or alkaline, and numbers below seven down to zero are considered acidic.

Most plants prefer a slightly acidic pH balance—somewhere between 6.0 to 6.5—but depending on your strain type, grow medium and nutrient program, this range can vary.

pH Levels & Your Garden

Grow medium, or substrate, is probably the single most important aspect to consider when thinking about the pH of your garden.

For instance, pure peat moss is known to be more acidic than most mediums and should be accounted for. Most soilless mixtures will do well with a pH between 6 and 6.5, as they have medium CEC levels of around 50 – 60.

However, when you get into more advanced hydroponic mediums, such as Rockwool or HEC (expanded clay balls), lower pH levels are recommended. These substrates are sterile and inert with a CEC of zero. Recommended pH levels for these grow mediums range between 5.6 to 6.2. With these grow mediums, even pure water at a neutral level of seven is too acidic and could benefit from an adjustment using a “pH down” additive.

HEC media performs better with lower pH levels of around 5.8 – 6.0.

A good rule of thumb, no matter what type of grow medium is being used, is to never go over 6.5 on your pH meter—otherwise absorption of your nutrient solution will slow drastically, especially in water culture systems.

And in both hydro and soil systems, if you notice deficiencies in the lesser, micronutrients such as iron, zinc or manganese, lowering your system’s pH to between 5.0 – 5.5 for a week could help increase your CEC and thus your roots’ uptake of these minerals.

Thanks for reading everyone and remember, grow… and help the world grow, too!

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