The science of PH

[Hushpuppy]

Is there anyone who can explain why there is a difference in nutrient absorption for differing PH levels from soil to hydro. There seems to be a concensus for the best PH for hydro being 5.8-6.0. But for soil there is more variance for the best value of PH for optimum absorption. I hear many of the more experienced soil growers say 6.4-6.6 is best, while others say a little higher is best.

I found for my organic plants that they did quite well keeping them between 6.6-6.8 but my Bro says that he runs his hydro around 6.4-6.7 and has very nice harvests. I also have found that by constantly allowing the PH to swing from 5.0 to 6.3 in my hydro system that my plants stay green right to the cut. I let them run to 9weeks (for 8-9week plants) and I get NO yellowing off. I don't know if that is a good thing or not but they stay green and healthy looking right to the cut.

I check my trichomes before harvesting to make sure I am at peak but suspect that they could easily go for 1-2 more weeks without issue for some. A couple of the 8wk plants start showing nanners at 9wks and have fully cloudy trichs so get cut. but none show the late flowering "die back" that I see in the organic plants.

My question is why does the best absorption level change for plants in hydro and plants in soil. And what is the driver for this PH level controlling absorption.

 

[ShOrTbUs]

subbed! and hoping for a wall of text from someone

 

[zem]

I read a few times about this, the analysis was that plants themselves need a ph of 5.8 average like in hydro and when you water with 6.5 in soil you are kind of balancing the tendency of soil to acidify

 

[Rosebud]

Go all organic and it doesn't matter. I hope you get it figured out Hushpuppy. Good thread.

 

[Hushpuppy]

The organic method is another avenue that adds to the same question. As you said Rosebud, with organic growing, maintaining PH isn't necessary(if your source water is within the proper PH range). It is my understanding that the microbes either ballance the PH with their own actions or negate the PH issue by making the nutrients available to the roots for absorption.

So the question with them is: do the microbes just bypass the PH issue or are they taking care of the PH maintenance for the soil grower?

My question is really just acedemic as I have no trouble maintaining PH and having really good harvests. The scientist in me is always questioning and wanting to learn more

 

[DrFever]

To understand how ph works in different mediums we have to look further into it we look at nutrients as just that nutrients , but when examining closer in a chemists eyes ??? there are molecules and ions that have electrical conductivity under different ph ranges
Water as we all look at it is wet , fluid like substance but looking closer it is a molecule H20
pH is a scale that chemists use to measure acidity. Values below 7 are considered acidic, values above 7 are alkaline ( the opposite of acidic) and 7 is neutral.

Most plants can tolerate a wide pH range in solution culture, but they cannot tolerate a wide range of acidity in the soil.

When soil acidity changes, the solubility of a number of metal ions also change. Plant growth is really affected by the varying concentration of these metals in solution rather than by the acidity itself.
Under acidic conditions, many soil minerals dissolve and increase the concentration of metal ions to toxic levels. The primary toxic metal is aluminum, but high levels of manganese and iron can also inhibit plant growth under these conditions. The nutrients phosphorus and molybdenum are less available in acidic soils and calcium and/or magnesium may also be deficient.
Under alkaline conditions, the solubility of minerals decrease to the point that nutrient deficiencies occur. Plant growth is therefore limited by deficiencies in iron, manganese, zinc, copper and boron. Phosphorus is also less available in alkaline soils and high levels of calcium may inhibit the uptake of potassium and magnesium.
The aim in managing soil pH is not to achieve a particular pH value, but to adjust the acidity to the point where there are no toxic metals in solution and the availability of nutrients is at its maximum. This condition is usually achieved when the soil pH is between 5.8 and 6.5, however some plants have special acidity requirements.
Limestone is used to treat acidic soils, but the soil pH value alone does not indicate the amount needed. An exchangeable acidity analysis must also be done to determine the amount of limestone required, and the soil calcium and magnesium levels must be analyzed to determine which type of limestone (dolomitic or calcitic) is required.
Some alkaline soils can be acidified using sulfur or acid forming fertilizers, but soils with free calcium carbonate cannot be easily acidified. It is often easier to manage the nutrient deficiencies that occur on alkaline soils than to acidify the soil.

In hydro systems PH has to be maintained constantly, : pH is important because it affects availability and absorption of several of the 16 atomic elements needed for plant growth. Maximum absorption of these elements is found at pH readings 5.5 to 6.5. When pH falls below this range many of the macro elements (N, P, K, etc) have less availability, and absorption of the micro nutrients can reach toxic levels.
so breaking it down when we feed our plants in soils the molescules/ gas exchanges occur breaking minerals down for plant uptake so higher ph is needed for this process
, in hydro were literally injecting nutrients into the plant in pure form so less ph is needed as not as much gas exchange and other process occur if that makes any sense ??

 

[Rosebud]

"So the question with them is: do the microbes just bypass the PH issue or are they taking care of the PH maintenance for the soil grower?"

I believe the microbes take care of the PH.

 

[DrFever]

"So the question with them is: do the microbes just bypass the PH issue or are they taking care of the PH maintenance for the soil grower?"

I believe the microbes take care of the PH.

Many organic sites state that simply adding microbes will make a remarkable difference in plant health. This is not always true. In some cases the additions of certain microbes will help greatly, but in other situations it will only be temporary at best.
When talking about increasing microbial activity, it is also important to remember the other factors that must be considered. Beneficial soil microbes are living organisms that are subject to their environment. Like most all living organisms, they must have air, water, acceptable soil temperatures, proper soil chemistry for growth, and an abundance of food to survive and grow. If one of the necessary items are missing, the soil microorganisms will decline. Remember, the work associated with these beneficial soil microbes are the only means of converting organic elements into forms the roots can take up and use. If they decline, so will your grass and other plants.
so for your answer is no organic matter keeps ph in check manures etc

 

[jmansweed]

Rosy.....I have lots of info on pH. I'll cut and paste a few paragraphs from a recent write up I did on the subject that may help answer your question (some of it may be out of context) - It's a bit winded but here ya go - I omitted the last few sections :

Arguably, no problem plagues more growers than maintaining pH. To understand pH and it’s relationship to marijuana, and plants generally, we first have to dive into some details about nutrient absorption and plant growth. This requires another complication however, pH is regulated differently depending on our grow methods and mediums. For this conversation I’ll broadly discuss three indoor options; organic soil, non-organic soil and hydroponic gardening.

pH is important to us as growers, and more importantly to our plants, because it represents a major nutrient absorption regulatory factor we must control (or initiate) to properly grow plants. Plants absorb nutrients through water bound hydrogen osmosis. Osmosis essentially consists of passing molecules through the semipermeable membrane of a root system’s cells. pH means “potential hydrogen”. It is a measurement of how much hydrogen is in our medium and/or nutrient solution. Every time nutrients pass through a plant’s cell membrane it must be accompanied by a molecule(ion) of hydrogen or hydroxyl. If there is a high concentration of hydrogen in the medium it is considered acidic, and a low hydrogen concentration it is referred to as basic and/or alkaline. Likewise, a high level of hydroxyl means the medium is alkaline and low levels then mean the medium is acidic. A scale of 0 to 14 is used to describe the range of possible acidity levels, 0 being extremely acidic and 14 being extremely alkaline. 7 is considered neutral. For example, standard bottled water is usually 7.

Hydrogen molecules are positively charged ions and hydroxyl are negatively charged. Standard water has a known balance in regards to these ions, therefore we can predict the levels of positive and negatively charged ions through only measuring one or the other. pH measure positive hydrogen ions. As water reacts with nutrient salts and/or microbes, the charged ions bind to some nutrients and repel others. Controlling these ion levels dictates how acidic or alkaline solutions will be and therefore, how effectively roots will absorb nutrients. All these charges equate to electricity.

Electricity is the influence that starts many reactions we’re concerned with, creating the foundation of our inputs. Prior to nutrients being absorbed, all the nutritional ingredients are broken down into nutrient salts. These salts conduct electricity between them. EC is a measurement of that conductivity and hence describes how dence in various salts our medium is. If the EC is high, vital nutrients will not be absorbed. The opposite occurs as well. As your EC climbs and lowers ,pH fluctuates, developing nutrient lockout, deficiencies, and sometimes death all together.

Measuring pH consists of a few methods. Simple litmus test papers with a standard color comparison kit are common, as well as liquid tests where-as a chemical solution is added to again compare to a standard color chart. There are also high tech models measuring EC, pH and ppm with temperature compensation using digital displays.

Organic Soil :

Under organic soil conditions there are some interesting and revealing methods to ensure proper pH control and hence absorption. Organic soil for this conversation refers to non-chemical and non-synthetic nutrient enriched mediums that promote natural ecological relationships. This is a system evolution has created and one we can easily replicate with the right ingredients. No method has proven more consistent for me, than relying on the natural system plants and soil life develop together. Under these conditions my approach to pH has been basically hands off. I allow the living soil of bacteria and fungi and it’s relationship with plants dictate how pH is maintained. Typically around pH 6 to 7.

Healthy, organic soil is rich with life. If we were to take a sample and look through a microscope we would actually see a combination of countless living organisms, organic matter and minerals - billions of living microbes populate only a tablespoon of soil. For this discussion, the microbes we are concerned with are primarily various bacteria and fungi. As the root system of our plant penetrates this underground mayhem of microbial life, it releases certain chemical signals and fluids that actually attract some of these microbes. The microbes, most of which lack the ability to produce energy, ( ie. photosynthesis), happily work with the root system. When plants absorb most nutrients, it is actually an exchange between soil organisms and the plants. Above ground, when photosynthesis occurs, some of the energy is stored in a packet of sorts - referred to as ATP (adenosine triphosphate). These packets are a good example of what the plant has to exchange. Microbial life is great at breaking down organic matter in soil. Both fungi and bacteria release enzymes to digest the nutrient and then essentially absorb that nutrient back into themselves. This gives the microbe a commodity to trade with the plant and that is just what they do. In this case, ATP for nutrients. This exchange can consist of different products and different nutrients depending on the microbe and what the plant is looking for.

Flowering plants, like Cannabis, require a variety of nutrients during various stages of growth. A root system then releases items, (referred to as exudates), that attract specific microbes that can obtain the desired nutrient. Provided the microbe is present, an exchange occurs and each life form obtains the necessary component desired. Why is this knowledge pertinent to pH? It is these microbes, plant exudates and resulting exchanges that ultimately regulate pH under organic conditions.

Broadly speaking, bacteria and fungi are opposing forces in the regulation of pH. Bacteria tend to thrive under more alkaline conditions. The enzymes released by bacteria actually will raise the mediums pH over time. This also is very apparent for those of you who have brewed compost or nutrient teas. Bacteria populate oxygenated water and soil mediums rapidly and quickly raise your tea’s pH. Fungi takes longer to establish populations and releases enzymes that lower overall pH. This means we as growers try to provide ingredients that promote short term bacteria populations and long term fungi populations. When these microbes are balanced and a healthy relationship with the root system is established the pH will naturally be regulated.

What does all this mean for us as growers? Established issues with organic soil typically mean unintentionally poor soil mixes or the added organic soluble nutrients promoted one population of microbes over the other. Testing the pH of the runoff from your pot will help expose the issue if one occurs. A decidedly low pH implies bacterial populations probably have diminished and the opposite implies fungi needs support. The grower’s reaction to a wavering pH under organic conditions is important. The solution surrounds promoting life rather than altering your medium chemically and/or synthetically with pH controllers. pH controllers will indeed create a temporary solution and momentarily help your plant absorb available nutrients. Life however, is not temporary and without balanced microbial life a return to the issue will most likely occur. pH is naturally regulated under organic conditions in soil. Perfecting the soil mix and adding the proper ratios of liquid nutrients is the answer to wavering pH issues.

------Hope that helps a bit---------

 

[Hushpuppy]

Thankyou Jman Much props for that well written explanation. I am now understanding better, this thing that I am continually wrestling in my grows.

Its interesting to me that when I had my organic plant setup among my hydro plants, the PH was a far less battle with the organic than the synthetic setup. As you said, when I mixed up my organic nutes, I had to let it set so that the microbes had time to balance out before adding it to the auto-watering system. Once it ballanced out and was added, the system stayed dead on at 6.8 throughout, and only wavered when I had to add more nutrient tea.

I now understand that it is the relationship between the microbes themselves as well as their relationship with the organic matter in the soil/nutes that gives us the PH levels. The question then becomes: for organic setups, when monitoring PH at startup or some necessary water change, or even with the water/nute tea, what is the optimum PH to look for, or to bring nuted/unnuted water to before adding to plants or watering system?

As for synthetic hydro setup: I don't know if I have found some magic solution for maintaining healthy plants, but it seems to me that (for me at least) allowing the PH to "swing" from around 6.4max down to 4.8max(or vice-versa) is better for giving the plants all of the nutrients that they need, than to try to hold the PH in one position. Given the natural "swing" on the microbe level with the plant and microbes changing the chemistry back and forth(more as result than intention) to accomodate the differing needs of the plant; it seems that my method of PH "swing" or "drift" may be closest to immulating the natural rhythms of organic growing.

Or I may just be full of it

At any rate; thankyou everyone for adding to this conversation If anyone else wants to add to it, please do as sharing info and questions is how we all learn

 

[Rosebud]

Jmansweed, thank you so much, what a well written article. It is much more than just a symbiotic relations ship between the soil and the microbes. I have never ph'd and haven't needed too. Thank you again. wonderful.

 

[jmansweed]

"The question then becomes: for organic setups, when monitoring PH at startup or some necessary water change, or even with the water/nute tea, what is the optimum PH to look for, or to bring nuted/unnuted water to before adding to plants or watering system?"

Well Hush, defining exactly what pH the plant is looking for takes investigation and recorded study. Different stains will demand small differences in pH depending on what the plant prefers and what stage of growth she/he is at. This is one reason I often promote working with one strain over and over again. So we as growers not only can define pH numbers for that specific strain but more so, because it helps us develop an understanding of the intricacies involved with creating environments specific to growth demands.

I designed and ran an urban farm for years in Northern California. It was all vegetables grown hydroponically in closed loop, off grid systems. They were solar powered systems with environmental control and automated 12v pumps. More importantly it was all organic. Maintaining pH in hydroponics working organically is challenging. Algae, slime molds, and various forms of life developed living off excess nutrients. I had to study an old mentor of mine, Dr. Reams. He studied how matter equates to energy, and energy to matter. This led me to develop feeding schedules that only applied enough nutrients for optimum growth and little more. That only happened after studying what kind of life I was unintentionally growing in my reservoirs and then eliminating whatever excess nute it was feeding off of. It took over a year of research but the company now has a firm grip on organic hydroponics. My point is, finding the right numbers is just that with organics. It is not a matter of controlling numbers but more so, feeding your medium the correct ratios so the various microbes and root system can regulate numbers.

All of the actions relavent to direct absorption occur in the Rhizosphere, the area surrounding the roots of your plants. With healthy soil, your added organic solutions can vary in pH, and so can the medium. This minute area around your roots however, stays steady at whatever optimum number it sees' fit. As I mentioned earlier, bacteria tend to flourish quickly, raising pH in your teas or mediums. I add most of my teas at a decidedly low pH - sometimes as low as pH 4. Only a short time after soil bacteria interacts with the solution however, pH raises to an appropriate level until the counterbalancing effects of fungal life reacts with it.

Another important thing to consider are the basic elemental reactions occurring. I'll post one more section from the article discussing non-organic mediums that may reveal more about the "non living" reactions that have influence over pH. I follow up with maintaining pH in hydroponics but truthfully I simply have not had time to finish it - maybe in the next few days I'll post all of it together - none the less, here it is........and again, my apologies if some of it is out of context:

Non-Organic Soil :

Any time we add synthetic and/or chemical nutrients to our medium, it is no longer considered organic. This leaves us with a broad range of growing methodologies. You could be 90% organic and the 10% of synthetic additives you used negate the ability to truly call your grow organic. This means often times your medium can respond as discussed above as many “non- organic” mediums also have living pH regulatory systems. If however, you use soluble chemical and/or synthetic nutrients, and rely on a more science driven feeding cycle then the following most likely applies.

Most synthetic/chemical nutrients are chelated and often times, pH buffered. This means they have undergone the process of being somewhat digested enzymatically and/or chemically and are immediately available for plant absorption - or - they are provided in a ready to absorb synthetic nutrient salt. All nutrients ultimately break down into salts. When buffered, it means there are included ingredients that prevent any unusual spikes or drops in pH. There is no need to promote soil life here. In fact, most synthetic/chemical nutrients deter microbial life. Not to imply all microbial life dies but it develops an environment not indicative to flourishing populations.

pH can fluctuate for a number of reasons here. Blending organic material in a medium that lacks heavy populations of microbial life for example, can promote unwanted acid producing bacteria (anaerobic) and invite pathogens or simply rot. Synthetic (and organic) nutrient salts easily build up developing an unbalanced electrical conductivity (EC).

Lets consider a synthetic medium devoid of pertinent organic life, and how pH changes on a more scientific scale. When we simply add water to a medium it usually becomes more acidic as hydrogen naturally will replace some important minerals such as magnesium, calcium, phosphorus and potassium. As the level of hydrogen increases, the scale of acidity lowers. Water consists of 2 hydrogen ions and one oxygen molecule (H2O). Everytime we water our plants, we change the chemistry of the medium. In the majority of standard mediums, water molecules combine with the available carbon dioxide forming a weak acid, known as Carbonic acid (H2CO3). This weak acid reacts to it’s environment by ionizing or slowly separating and binding with other elements of the medium.

When carbonic acid (H2CO3) contacts calcium it releases it’s secondary hydrogen ion and carbon ion. This hydrogen replaces the calcium particles in the medium first. The now released calcium binds with the carbon to form calcium carbonate. Calcium carbonate is soluble and leaches from the medium. All of these reactions slowly acidify the medium. After calcium, alkaline elements like magnesium become soluble and can leach as well. This is why calcium and magnesium products raise the soils pH when added to the mix regardless of organic or inorganic methods. Understanding chemical reactions in your medium is vital to controlling it’s pH. This is merely the science of one specific reaction - there a hundreds if not thousands that occur with fertilization. To maintain proper nutrient content, a robust root system and healthy medium we must predict fertilization ratios that provide enough elemental ingredients to allow the actions of natural functions while additionally promoting surplus production.

We now know simply water will acidify a medium that contains little organic biomass. One way to combat this is through aeration. Adding air to our medium increases available carbon actually helping to maintain calcium content. It promotes phyto-chemical reactions within our root system and natural ecological reactions, increasing nutrient absorption. A medium devoid of typical organic life still pulses with elemental actions. Promoting these actions and increasing the volume of these reactions will help in regulating pH.

Maintaining and controlling pH starts with the choices we make in terms of our medium’s ingredients. Peat and Coco based mediums are naturally acidic to begin with. Soils heavy with clay will be naturally higher in pH. Creating good drainage is imperative as well. Air circulation around root systems increases activity and allows water and nutrients to saturate effectively. Adding calcium and magnesium to the soil helps “buffer” pH fluctuation. These elements are provided in different ways. Typically, cannabis growers mix in powdered dolomite lime, or calcitic lime, dolomite containing higher levels of magnesium and calcitic lime providing higher calcium requirements. This can assist in maintaining the pH and importantly can prevent rises above 7 or so.

After a medium foundation has been established, maintaining pH throughout the grow takes some observation and preventative actions. A schedule of regular pH testing should be adhered to even when things are running smoothly. I typically suggest testing your water source monthly, testing your nutrient/water solution every time you mix and finally, the run-off from your pots at least once a week. Remember as the plant absorb nutrients, the EC of your medium lowers and usually raises the pH. Small fluctuations should and will occur. Record your data keeping careful note of changes in your feeding schedule and how pH reacts. Eventually this helps in developing consistency. There are many soluble items that raise and lower pH. Dozens of companies make products for this reason alone. Acids from citric acid to phosphoric acid are used to lower pH. Calcium and magnesium blended agents are the most common items used to raise pH.

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I love this stuff - great thread

 

[Locked]

Thanks jman....I can actually get my head around that. I appreciate the info.

 

[Rosebud]

What are the affects of moisture content and microbe activity? If you let a plant dry to almost wilt, are the microbes killed? And what if you really soak your plant, are they drowned?
Thank you again for this read. Very very helpful.

 

[AluminumMonster]

Jman that should be stickied great post and easy to read.

 

[jmansweed]

Rosy, The simple answer is many microbes need water to survive, however depending on the microbe we're discussing some can remain dormant for long periods of drought only to begin functioning again after contacting water. Others absolutely will die off with drought. Typically, the microbes we're most interested in do require some level of moisture but again the heart of activity is within the rhizosphere. Here moisture is maintained even when your medium appears dry. (not indefinitely - lack of moisture will kill the plant eventually)

Microbial life releases enzymes that actually bind your soil together. This is why healthy soil maintains its' shape even when you pull the entire ball and medium from your pot. If it crumbles to dust for example, you know microbial life no longer thrives at any level.

With floods or a heavy application of water we will not eliminate all of our microbes but certainly can dilute the medium of some specific items. For example, calcium and mag. leach easily at times. More importantly however, it depends on the amount of air in the water. Using aeration, Many hydro growers will submerge roots for the entire grow with no ill effects. To microbes, drowning is not about being overcome with water but more so because of a lack of air.

 

[Rosebud]

Thank you! I have wondered that forever and I thought that just because the plant feels dry it still has enough moisture for a microbe. Thank you again. This is awesome.

 

[Hushpuppy]

Awsome read Thankyou Jman for sharing your knowledge. I find this stuff fascinating. I totally agree with you on repeatedly growing one strain so that you can get to know the plant's needs and quirks.

I have to wonder if aeration/oxygenation of the medium is a good thing, would it be better to involve an oxygen concentrator/generator in the aeration system of a larger grow so that a higher level of oxygen is delivered to the rhyzosphere, or is the general atmospheric level of oxygen enough when pumped in through said aeration system.

 

[Rosebud]

I use a pencil HP.

 

[jmansweed]

HP - aeration is more important than strictly oxygenation. As you mentioned, general atmospheric conditions typically allot enough O2 for your root system. Almost all atmospheric gasses are used by the microbial life as well (lots of Nitrogen for example), so in my experiences, general aeration is sufficient.