PH values for growing Cannabis

Blue Planet Nutrients;1390271 said:

Wow....some debate going on in here! I like it!!!
If I may, please allow me to toss my 2 cents into the debate. I am not claiming to know it all but here it as I understand it:

First off, I think that I read something about fungus and low pH earlier in this thread so let me touch on this first. Fungal growth is optimum at a pH right at 7.0 and anything lower than that will severely restrict it. Most of the peer-reviewed scientific material I have read shows a negative relationship with decreasing pH and root rot and fungal infections. In fact this goes for just about all microbial growth and pH. I have observed over and over that a low pH (below 4) will shut down bacterial and fungal growth almost completely.

pH and nutrient availability:

I am going to focus this on hydroponics because in soil, roots can actually modify the rhizosphere (zone immediately surrounding the roots) and change the pH by up to 2 units which will modify nutrient uptake significantly. Hydroponics is different because the nutrient solution is constantly circulating and the roots can't modify the immediate area surrounding them as well.

Now, most of the pH data that I have read stems from pH observations of nutrient availability in soil. This goes for most of the scientific literature about hydroponic culture that I have read. First and foremost, Different plant species thrive best at different pH levels due to the fact that each plant species require certain nutrients in different amounts compared with other species so it is intuitive that different plants will grow better at varying pH levels because it is fact that certain nutrients are more or less available at varying pH levels. Google, "Argo and Fisher, Understanding pH Management". That will provide more insight on the nutrient needs of many plant species and how pH variations affect nutrient availability because we all know as a fact that the pH directly effects nutrient availability.

But who cares about tomatoes and okra, we want to know about Cannabis.

Well, I haven't read too many scientific journal articles about cannabis and pH because simply, there is not a lot of peer-reviewed material available about growing cannabis. They simply don't exist. Google "cannabis and growth and pH level hydroponics" or any other similar combination of words. You will find that the results are mostly
"here-say" on forums and other folks that claim to know what they are talking about, but....very few, if any, scientific journal articles that are reviewed by scientists for accuracy and legitimacy. There simply isn't much reliable data out there to back up most claims and hypotheses.

So....we need to go off of what we all have observed as growers as far as what works and what doesn't. We also know as fact that pH affects the availability of nutrients. What pH is best for cannabis? Well, what nutrients does cannabis need in what amounts at which stages of growth (veg vs. flower). Is it fair to say that as a plant matures, nutrient requirements will shift from nitrogen to phosphorus and potassium with micronutrient and secondary nutrient requirements basically staying similar? If so, then as the flowering phase continues, P and K are more important so slightly higher pH levels will benefit plants (around 6.0 for more P availability) but let get too high, and Fe will become a problem unless you are using a chelate such as EDDHA. Too low a pH and magnesium and calcium definitely can become less available.

IMPORTANT: pH isn't everything, varying amounts of cations vs. anions as well as the ratio of certain nutrients vs. other nutrients will affect nutrient availability as well. For instance, we know that cannabis likes magnesium and magnesium deficiency is very easy to spot. Well, Magnesium (Mg+) is a cation and competes with other cations like NH4+, Ca++, K+, Fe++,etc... at exchange sites (exchange sites mostly referring to soil but cation/anion cation/cation interaction is very important in hydroponics as well). Cations will interfere with each other which will affect the uptake and availability of these cations. Simply stated, if the cation/anion or cation/cation balance is not ideal or at least balanced, that alone can be a cause of nutrient deficiency regardless of pH level. That is why it is important to change your reservoir weekly to avoid these imbalances because nutrients are not used at the same rates and after some time, your reservoir nutrients will quickly become "unbalanced". I must mention this because this is outside the realm of pH management and can effect nutrient availability and uptake. This is very important because not everyone has the same water profile and folks using very hard water with lots of calcium and magnesium will experience different problems and have different results as someone using RO water or someone using water with a mineral profile that makes it acidic rather than basic.

Ok, back to pH levels. Much empirical evidence has shown that cannabis thrives at a pH of around 5.8 in hydroponics. This is because the nutrients that cannabis needs are balanced and readily available at this pH. Different nutrients are available at different pH levels and there has to be a balance where everything can reach a happy medium. I have personally observed that lower pH levels (5 to 5.5) seems to be ok with cannabis and some vegetables and I have actually seen them perform better at times at lower pH levels. I have also observed that pH levels of 5.5 to 6.2 offer great growth conditions as well for cannabis in hydroponics. What does this mean? Well, in my opinion, there are a few factors affecting the nutrient availability in nutrient solutions besides just pH.... cation/anion balance, water quality, etc... So, my thesis is this: Growing cannabis hydroponically is best accomplished at a pH of between 5.2 and 6.2. Find what works for you and run with it. There will be pH fluctuations throughout a 24 hour period as well as during the week as your nutrient solution is depleted. Keep it close to 5.8 which is a value where all nutrients are readily available for plant uptake in cannabis and you will do fine. Some fluctuation around this value is great and expected. I hate to come up with such a general and blanket analysis but hell, I have seen many successful hydroponic grows and not all of them had a pH of exactly 5.8 the entire way through. Most of my grows have dropped down in to the low 5's due to my water profile and I have had great results...

This is a great debate and I welcome anyone to help me fill in the gaps...

Click to expand...