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soil Soil pH

Soil Biology and pH by Jeff Lowenfels
 
The success of the AeroGarden, the first plug-and-grow aeroponic kitchen appliance, is testament to the fact that ordinary people do not understand the concept of pH and don't want to deal with it in their growing situations. Make it so you can practice hydroponics without this chemistry barrier and they will come, apparently.
 
Frankly, the concept of pH also confuses soil gardeners. Heck, the definition of pH was inadvertently reversed in my book "Teaming With Microbes: A Gardener's Guide to the Soil Food Web." (Yes, some readers noticed; I received two "you made a mistake" notes. But that's not as many as I thought I'd receive.) Fortunately, the mistake was corrected in time for the second printing.
 
In any case, soil gardeners have been told certain plants require acidic conditions- for example, rhododendrons and azaleas- or else they won't grow. The solution advocated by most experienced gardeners is not dissimilar from what a hydroponics grower would do: adjust the pH with chemicals, such as agricultural lime, to make the soil more alkaline. To make alkaline soil more acid, we are told to add sulfur. Because they are chemical changes, these solutions work for a short time. But to me pH is a biological matter.
 
A bit of quick pH review is in order (if only to make amends for the mistake in my book). You may remember that pH is a measure of the acidity or alkalinity of a solution on a scale of 1 to 14; 1 being most acidic and 14 being most alkaline. A more technical description is that pH is the measurement of the concentration of hydrogen ions, H+. If you have lots of H+, the pH is low, or acidic. If you have few of them, the pH is high, or alkaline.
 
If you are adding fertilizers and using chemicals, you are stuck in the chemical realm. Organic gardeners, soil food webbies in particular, realize that pH has more to do with biology than it does with chemistry. That's because of the way plant roots take up nutrients. Root hair surfaces are covered with positive electrical hydrogen cations. Think of these charges as ping-pong balls. If soil particles are small enough, their surfaces are covered by these ping-pong ball charges, both positive (cation) charges and negative (anion) charges. These cations are not limited to hydrogen; they also include calcium, potassium, sodium, magnesium, iron, and ammonium. All are important plant nutrients.
 
When a root encounters a clay or organic particle, it can exchange one of its hydrogen cation for another positive one from the particle. It can choose from calcium, potassium, sodium, magnesium, iron, ammonium and hydrogen, as these are all cations carried by clay and silt and are all, as luck would have it, major plant nutrients.
 
This is known, incidentally, as cation exchange capacity, or CEC. Sand and silt have low CECs, because they comprised of particles that are too large to hold electrical charges. This is why humus and clay are needed to make soil good. They are extremely small particles and can carry cations.
 
So, back to pH. Every time a plant root exchanges a hydrogen ion for a nutrient ion, it increases the concentration of hydrogen ions in solution. Thus, the pH goes down and things should become more acidic.
 
Ah, but things usually balance out because the positive cations on the root surface also attract negative charges. Here, hydroxy ions (OH-) are the exchange ping-pong balls, and addition of hydroxy ions lowers the concentration of hydrogen ions in the solution, and pH goes up.
 
I know this still sounds like chemistry and not biology. However, each plant has an optimum pH requirement. What soil growers need to know (and hydroponics growers don't) is that the type of bacteria and fungi attracted to a plant's rhizosphere by the plant's exudates has a lot to do with setting this optimal pH. Bacteria produce a slime that raises the pH, and fungi produce acids that lower the pH. Since the plant is in control of the biology it attracts, in a natural system, it is the plant that determines the pH, and not some chemistry teacher.
 
So, while you may forget the chemistry of pH, at least remember there is a biological side. Do no harm to it, and you shouldn't have to worry much about pH when you grow plants in soil. Moreover, the nutrient exchanges that occur above also have a lot to do with what kind of bacteria and fungi are attracted to the root zone as some like higher pH and others lower pH.
 
Great post!
 
As a chemist, I slightly disagree with some of your definitions/descriptions of pH in these systems.
 
However, I know audience is everything, and it was very clearly explained. I 100% agree with your conclusion. After all, somehow these darn plants survived before we came along. Plants can do a lot with a little (it might just take them awhile), it's usually just in horticulture/agriculture when the grower is trying to ride the fine line of optimum conditions that these issues arise.
 
The way I like to see it, you can either stay in the chemical domain or the organic domain
 
The moment you start feeding with soluble chemicals, managing pH, PPM and EC become more and more important
Mimic nature as much as you're able to and embrace it, things will generally sort themselves out
 
But even if you're an organic gardener, you'll somewhat pay attention to PH.  This can be an indication of what's going on in your plants - if/when something does.
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Also, you have to be mindful of PH when STARTING new containers.  You cannot just plant out in peat moss, with no PH buffer and expect results.  Don't believe me?  Try it.  Something has to create favorable conditions for the start of your microbe colony.  Once it's started, you have little to worry about.
 
solid7 said:
But even if you're an organic gardener, you'll somewhat pay attention to PH.  This can be an indication of what's going on in your plants - if/when something does.
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Also, you have to be mindful of PH when STARTING new containers.  You cannot just plant out in peat moss, with no PH buffer and expect results.  Don't believe me?  Try it.  Something has to create favorable conditions for the start of your microbe colony.  Once it's started, you have little to worry about.
hey Sold7 my friend,  it's pH not PH.     :party:
 
Powelly said:
I wouldn't grow in 100% peat moss no, doing so is not growing in soil and outside the scope of this article
 
Fair enough.  However, a very large percentage of growers here grow in containers and/or hydroponics, so I don't think that was fully clear from the beginning.
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That being said...  There are some areas where it's very difficult to get the native soil to retain organic matter.  When conditioning soil plots, early measurement of PH (because I like writing it like that) is an indicator of the progress of the conditioning.  And you wouldn't plant out before you knew your system was established, lest you waste your time.
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I appreciate what you're selling, but with caveats.
 
Solid7, you really need to start listening properly instead of just thinking about your next answer
 
This thread isn't about monitoring progress with a pH meter, it's about adjusting pH by chemical means in an organic soil vs non-organic environment
The fact that a lot of people here don't use soil is irrelevant
 
I have a plot of land that I adopted, it was former bushland that was developed on previously before being marked as a bush for life site
When I started 5 years ago it had been wiped out by a bushfire and was simply bare soil that cracked when dry and you couldn't dig into
All I did was cover it in leaves and then plant perennial grasses - now it's a jungle and recovered easily from a second bushfire 2 years ago
 
I did actually check pH a number of times with a device the forestry service had that you stick in the ground, the soil pH varied wildly from as low as 6 to as high as 8 depending on sunlight, rainfall and time of the day
 
Powelly said:
Solid7, you really need to start listening properly instead of just thinking about your next answer
 
This thread isn't about monitoring progress with a pH meter, it's about adjusting pH by chemical means in an organic soil vs non-organic environment
The fact that a lot of people here don't use soil is irrelevant
 
I have a plot of land that I adopted, it was former bushland that was developed on previously before being marked as a bush for life site
When I started 5 years ago it had been wiped out by a bushfire and was simply bare soil that cracked when dry and you couldn't dig into
All I did was cover it in leaves and then plant perennial grasses - now it's a jungle and recovered easily from a second bushfire 2 years ago
 
I did actually check pH a number of times with a device the forestry service had that you stick in the ground, the soil pH varied wildly from as low as 6 to as high as 8 depending on sunlight, rainfall and time of the day
 
Just say your piece, and agree with valid points, and contradict everything that isn't, and move on.  Regardless of what you think, I'm not on a single-minded mission to discredit you.
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If you want to educate people, that's great; but because you put some leaves on the ground in the middle of Australian outback, doesn't mean that you know jack squat about creating fertile soil in Florida sand, for example.  That's what I'm trying to point out.  If some people just jump on your organic crusade, and say to hell with the traditional methods that are proven to work, then you may be setting some people up for failure.  It doesn't mean that your advice is bad - it just means that you haven't got the whole picture, and should strive to help people come to your side - even if in steps.  Contrary to what you may believe, I prefer your methods, and i'd actually like to see more people use them.
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Some people will jump, some will stir the water with their toes.
 
solid7 said:
If you want to educate people, that's great; but because you put some leaves on the ground in the middle of Australian outback, doesn't mean that you know jack squat about creating fertile soil in Florida sand, for example.  
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You live in FL and grow exclusively in pots, right? So you know "jack squat" about creating fertile soil in your backyard yet you malign others for their methods that work in their location? Just wondering......
 
Solid7's recent pix......
 
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Out of context much?
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So you choose to try to pick a fight by posting a cold damaged and hurricane damaged plant... ok, fair enough.
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The point of my counterpoint to the discussion was, that there aren't always easy peasy solutions. Care to know why I don't grow in ground? Or are you just being confrontational? This is a discussion, right?
 
Your counterpoint had nothing to do with growing in the soil, you were talking about peat moss and containers for some reason
 
Powelly said:
Your counterpoint had nothing to do with growing in the soil, you were talking about peat moss and containers for some reason
Yes, I still had it fresh in my head where you were talking in another thread about how PH buffering was a silly ridiculous thing - when in fact, the context there was, at least in part, hydroponics. So you'll forgive my blunder, as I forgive yours.
 
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