Cation exchange capacity and water retention rates list

[EnlightenedGardener]

Thank you all for this information. It seems that a higher cec goes hand in hand with higher water retention except for charcoal (according to the chart). I'd always thought charcoal would hold quite a bit of water. I wonder if the chart is assuming a certain particle size? The charcoal I have probably averages 1/12" - 1/8" in size.
I just mixed up some turface, diatomaceous earth, fir bark, and charcoal in equal parts to test on a couple tropical plants (not bonsai). Seems the ph may be on the high side but that cec and water retention will be amazing!
Wish me luck

 

[TN_Jim]

Wish me luck

Good luck

 

[Leo in N E Illinois]

Thank you all for this information. It seems that a higher cec goes hand in hand with higher water retention except for charcoal (according to the chart). I'd always thought charcoal would hold quite a bit of water. I wonder if the chart is assuming a certain particle size? The charcoal I have probably averages 1/12" - 1/8" in size.
I just mixed up some turface, diatomaceous earth, fir bark, and charcoal in equal parts to test on a couple tropical plants (not bonsai). Seems the ph may be on the high side but that cec and water retention will be amazing!
Wish me luck

CEC = cation exchange capacity is the ability to hold charged ions. CEC is an electrochemical property of the potting media. It has ABSOLUTELY NOTHING to do with water holding or water retention. The two are independant, unrelated traits.

That is why charcoal can have a higher CEC and a lower water retention capacity. One has nothing to do with the other.

Except. CEC is a property of a surface. Charcoal has many bonding sites available on its surfaces. Charcoal, typical hardwood charcoal, is not all that open, it does not have many internal surfaces. So it can not hold a lot of water. Its surfaces are fairly dense with bonding sites available for CEC. So charcoal holds little water but has a high CEC.

Something like Diatomaceous earth, has many surfaces, as it has thousands of tiny pores. The tiny pores means that there are many internal spaces in which to hold water. The number of bonding sites available for CEC is fairly low density, BUT because of the huge internal surface area of porous diatomaceous earth, there is a lot of CEC, and it holds a lot of water.

The two traits, water holding capacity, and water retention are not linked to each other. The property of internal surface area, and the density of CEC available bonding sites is where the two traits seem to be links, through the effect of amount of internal surface area.

While much is made of CEC, in terms of horticulture, simple adjustments in how we grow our trees makes CEC largely an issue that can be ignored.

If your water quality is good, CEC is a trivial issue. You can use low CEC media and simply just fertilize your trees more often. No big deal.

IF you are trying to compensate for very hard water, by using a high CEC media, well then CEC does become important.

For the vast majority of growers, with medium hardness irrigation water to soft rain water, CEC is a trivial problem that is safe to completely ignore. Only those trying to compensate for hard water is CEC something worth worrying about.

 

[River's Edge]

You can use low CEC media and simply just fertilize your trees more often.

Excellent summary Leo. one simple additional thought! "Or choose a fertilizer that releases or breaks down slowly over time, instead of frequent repeated applications."

 

[0soyoung]

CEC = cation exchange capacity is the ability to hold charged ions. CEC is an electrochemical property of the potting media. It has ABSOLUTELY NOTHING to do with water holding or water retention. The two are independant, unrelated traits.

They are, in fact related. CEC is a measure of charges on the surface of the soil particles. Water molecules are polar. Water wets the surfaces of soil particles, more so the higher the CEC, IOW, higher CEC media does, in fact, hold more water. Stronger surface wetting means higher capillary water columns (all other things, particle size and etc., being equal).

 

[Rivian]

Why is high CEC good for people with hard water?

 

[Leo in N E Illinois]

Why is high CEC good for people with hard water?

Not everyone thinks high CEC is useful for people with hard water. Short term, CEC can actually soften the water by binding up the calcium in the irrigation water. BUT as soon as all the bonding sites are saturated, this effect no longer happens. Even with fairly high CEC media, sites can be totally saturated by 300 mg calcium carbonate per liter water in a matter of a couple weeks. After that, more or less the high CEC media that is saturated behaves mostly like any other media. There are some minor details, but functionally for hort purposes, the high CEC media no longer offers an advantage once its sites are saturated. If you already have very pure water, low in cations, and use a high CEC media, this will allow you to raise salt sensitive plants for some time as it slows the build up of salts. But we are focused on Bonsai, not Carnivorous plants, so this is largely a moot point.

There is some evidence that a high CEC media, even when saturated with calcium and magnesium ions, will capture an hold fertilizer salts for some period of days, rather than just letting fertilizer salts just flush through. Nitrates, and ammonia along with phosphates and potassium salts will have some residence time in CEC materials knocking out some of the calcium and magnesium for a while. This makes fertilizer available longer after application.

So that is the general why

 

[Dale in MA]

Charcoal has many bonding sites available on its surfaces. Charcoal, typical hardwood charcoal, is not all that open, it does not have many internal surfaces. So it can not hold a lot of water. Its surfaces are fairly dense with bonding sites available for CEC. So charcoal holds little water but has a high CEC.

I know this is a very old thread but I'd like to come to the defense of charcoal, taking exception to the statement that it "is not all that open". I'm doing this for others who may stumble on this forum thread. Think about wood. Wood anatomy. Charcoal is the carbonized remains of a lot of xylem and, yes, xylem functions as tubes that conduct water. So I believe it is wrong to say that it is not that open. It may look like hard glassy chunks, but microscopically it still has the xylem structure and so it has an amazing amount of internal surface area. I think this is the the reason for the very high CEC values. And if charcoal is washed free of caustic mineral ash it should have a very neutral pH. It is light and so it is floaty like perlite. But it is amazing stuff. The basis of the extremely productive terra preta soils in the Amazon. It doesn't rot. I use it in long-term pottings of slow growing cacti (which are like natural bonzais) and Adenium obesum. I use it together with compost, and graded natural stream sands. Nothing bad to say about it.

 

[Leo in N E Illinois]

I know this is a very old thread but I'd like to come to the defense of charcoal, taking exception to the statement that it "is not all that open". I'm doing this for others who may stumble on this forum thread. Think about wood. Wood anatomy. Charcoal is the carbonized remains of a lot of xylem and, yes, xylem functions as tubes that conduct water. So I believe it is wrong to say that it is not that open. It may look like hard glassy chunks, but microscopically it still has the xylem structure and so it has an amazing amount of internal surface area. I think this is the the reason for the very high CEC values. And if charcoal is washed free of caustic mineral ash it should have a very neutral pH. It is light and so it is floaty like perlite. But it is amazing stuff. The basis of the extremely productive terra preta soils in the Amazon. It doesn't rot. I use it in long-term pottings of slow growing cacti (which are like natural bonzais) and Adenium obesum. I use it together with compost, and graded natural stream sands. Nothing bad to say about it.

I'm not sure what I was thinking back then when I wrote my 2022 comment. The topic of CEC quickly becomes gobbly gook in my head. A lot of that science-y stuff I used to quote has become jumbled in my head with age, or maybe COVID brain.

BUT in my personal 50 years of horticulture experience, for what ever reason, I have always found charcoal a key component to my orchid potting mixes and to a lesser degree to my bonsai mixes. All my various orchid mixes included 5 to 15% by volume hardwood charcoal chips in the same size range as my fir bark chips or other media. I would find roots firmly attached to the charcoal when repotting a year or two later.

Finding charcoal in the right particle size to blend with my akadama or kanuma or other aggregate mixes has been more difficult, but when I have it on hand I use charcoal at about 5% of the total mix by volume in my bonsai mixes

I don't understand the implications in terms of CEC and other science-y gobbly gook. But it is clear from experience and I do mean decades of experience, tree roots and mycorrhizae love to attach to the charcoal particles. I take that as a good sign. I will keep using charcoal when I can get it.

 

[FreshAirSunshine]

Yeah this thread gets into a lot of surface science stuff that’s a bit messy to trace all the way down to bonsai practice. Hydrophilicity and hydrophobicity to an extent correlate with water uptake, but water uptake usually is best identified by mass uptake, measuring heats of vaporization, or things like thermogravimetric analysis of a hydrated sample.

They CAN correlate with cation exchange capacity as many cations form stable hydration shells of water (sodium usually has 5-6 first shell water molecules I think, lithium is 4/8, etc.) so from a dried state with dehydrated cations, especially cations physically accessible to water and energetically unstable enough to exchange (touching on CEC here…), you can have water uptake correlate with exchangeable cations.

The challenge is other non-exchangeable cations (or less exchangeable) can also enhance water uptake. An example relevant to here would be surface hydroxyls (silanols or aluminols) on clays or silicas (sand) or zeolites (aluminosilicates like akadama I believe). These can also interact with water through hydrogen bonds to the OH hydroxyl groups, but they are far less readily exchangeable as they are covalently bonded to the material surface (versus a van der waals/ion-pairing of exchangeable cations in zeolites). As such, they greatly impact wetability but only slightly impact cation exchange (the proton/hydrogen from a hydroxyl group is far less readily exchanged than the proton from an acid zeolite).

The presence of these reactive protons on the surface and their ability to exchange is what acidifies water exposed to the material, leading to a lower pH.

Similarly, some materials bind protons or CO2 from ambient water, often present as carbonic acid from equilibrium with CO2 in air, making them basify the water relative to the mildly acidic water we’d have just based on CO2.

The interesting thing then is also how this all impacts things like nitrates, which are anions. What happens when you take a sodium or ammonium nitrate salt containing fertilizer solution and you expose it to an acid material is you form an ammonium-exchanged material and nitric acid in solution (in equilibrium).

I wonder how much of the effect is in the materials ability to wet and store anions and cations in forms more readily utilized by plants. I don’t know anything about plant biology though so that’s for someone else to comment on.

 

[Glaucus]

Charcoal is very porous aka open. Just google some electron microscopy pictures of charcoal. This surface area trait is the main reason it is used in things like filters and then named activated carbon. Not all products are the same, though.
Charcoal would be very water retentive if it had also been hydrophobic. The porosity is a key property for water retention. But if you repel water then it doesn't really matter.

pH affects CEC binding sites. For example silanol groups need to be deprotonated to become negatively charged and become cation binding sites. If you add more protons, ie lower the pH, more silanol groups will be protonated and become unavailable for binding. Same is true for active groups like sulfopropyl and carboxymethyl.

 

[Dale in MA]

I'm not sure what I was thinking back then when I wrote my 2022 comment. The topic of CEC quickly becomes gobbly gook in my head. A lot of that science-y stuff I used to quote has become jumbled in my head with age, or maybe COVID brain.

BUT in my personal 50 years of horticulture experience, for what ever reason, I have always found charcoal a key component to my orchid potting mixes and to a lesser degree to my bonsai mixes. All my various orchid mixes included 5 to 15% by volume hardwood charcoal chips in the same size range as my fir bark chips or other media. I would find roots firmly attached to the charcoal when repotting a year or two later.

Finding charcoal in the right particle size to blend with my akadama or kanuma or other aggregate mixes has been more difficult, but when I have it on hand I use charcoal at about 5% of the total mix by volume in my bonsai mixes

I don't understand the implications in terms of CEC and other science-y gobbly gook. But it is clear from experience and I do mean decades of experience, tree roots and mycorrhizae love to attach to the charcoal particles. I take that as a good sign. I will keep using charcoal when I can get it.

Glad you are still here! This was a very informative thread, but in the end I guess we come down to trying some of these things and seeing what works. I pull charcoal from my outdoor mud/cob oven - when it is hot enough for pizza - and put it in an airtight can. Kind of a carbon sequestration thing in addition to being great in the garden or pots. I crush it and screen it and the fines go into the garden. Someone (MoonUnitBotanica) on one of my cactus forums once said "100% that many people spend more on their potting mixes than the plants are worth" and that may be true. So we search for something cheap and available that makes our plants happy. Nice to be here mining your threads. I'm learning a lot.

 

[FreshAirSunshine]

Charcoal is very porous aka open. Just google some electron microscopy pictures of charcoal. This surface area trait is the main reason it is used in things like filters and then named activated carbon. Not all products are the same, though.
Charcoal would be very water retentive if it had also been hydrophobic. The porosity is a key property for water retention. But if you repel water then it doesn't really matter.

pH affects CEC binding sites. For example silanol groups need to be deprotonated to become negatively charged and become cation binding sites. If you add more protons, ie lower the pH, more silanol groups will be protonated and become unavailable for binding. Same is true for active groups like sulfopropyl and carboxymethyl.

Good point with regards to the deprotonation of silanols - my comment was aimed towards neutral or near-neutral acidic pH water. Silica’s generally have low pH points of zero charge, so you’d expect the surface to be negatively charged (as would be the case with deprotonated silanols) and able to exchange. The extent of deprotonation for silanols would still be lower than that of zeolitic Brønsted acid sites though.

 

[misfit11]

Are people still using Turface out there? I know it was big when I first got on BNut back in 2010 or so. I bought a bag (not cheap with shipping as there were no suppliers out here in CA) to try it out. I wasn't impressed. I saw slow growth rates and subpar rooting. At this point I stick to what works (APL) on my trees that are in refinement. I'm experimenting with perlite and coco coir for trees in development.

 

[River's Edge]

Popcorn and Guinness time!

Are people still using Turface out there?

 

[milehigh_7]

Are people still using Turface out there?

gosh I hope not…

 

[Leo in N E Illinois]

Are people still using Turface out there? I know it was big when I first got on BNut back in 2010 or so. I bought a bag (not cheap with shipping as there were no suppliers out here in CA) to try it out. I wasn't impressed. I saw slow growth rates and subpar rooting. At this point I stick to what works (APL) on my trees that are in refinement. I'm experimenting with perlite and coco coir for trees in development.

I still have Turface supply on hand, I'm blending it off into my grow out mix for younger stock at about 10% or so. At that level it does not seem to be harmful.

Pumice is my main ingredient. Akadama, Diatomaceous Earth in several particle sizes ( not just Napa 8822), fir bark, charcoal and other components go into my mixes.

 

[River's Edge]

My soil components include the following. Akadama, Pumice, Black Lava, Granite Grit and Fir Bark. All materials are sifted and combined with similar particle size depending on the situation. Keep fines for creating Muck, seed propagation. Sift to small, Med, Large based on the standard 3 screen bonsai sizes.
The components all have irregular shape to avoid compaction and retain air space. Pumice is the component that I use more of than any other component and I prefer a layer of larger pumice particles for a drainage layer in medium and large size containers.
Components I have used in the past and now avoid include Napa 8822, red lava and cheap brands of Akadama.
Exception is large grow beds for young trees developing. In this case I mix Sea Soil ( sifted ) with pumice for a combination of Organic and inorganic. 25% Sea Soil 75% pumice.
Note: I also reuse inorganic substrate by drying in the sun and sifting out fines before reuse! Basically new substrate for refined trees and recycled for larger containers nd grow beds with developing trees.
Cannot speak for turface, never used it.

 

[Dale in MA]

Seems most folks here don't like Turface. I've read some of the reasons. I want to get some clay into my mix without spending a lot. Not much for clay soils locally.
I am looking at clay cat litter and the EP Minerals SafeTSorb calcined clay product and trying to understand how it behaves before using it with plants. I really love the size of the SafeTSorb pellets. The cheap clay non-clumping cat litter I'm not sure about - a lot of fines and dust. I get the sense that many don't like the calcined clay/Turface, but most discussion I found was about root growth but not pH in particular. I like DE pellets and charcoal - they are both neutral pH - but they are both fairly light and I was hoping to find something with a bit more weight.

The clay cat litter mostly disintegrates in water. Putting about twice the volume of rainwater with it in a cup I get a pH of 4.1. I was not expecting this.

The SafeTSorb pellets in rainwater are very fizzy and active at first! Lots of fizz and bubbles. Again, I get a pH of the water = 4.1. Wasn't expecting that either.

I will rinse the SafeTSorb with fresh rainwater today and see if the acidification was a one-off reaction or if it continues to acidify.

Can anyone explain why the pH drops? Clay as a cation exchanger and might bind cations and release H+, but rainwater <should> have very little for cations. I'm puzzled.

Any thoughts will be appreciated.

 

[Leo in N E Illinois]

The imported substrates from Japan, Kanuma and Akadama ARE clay. They are clay derived from volcanic rock.

EP Minerals Safety Sorb if it says it is calcined clay then I would expect the same issues as with Turface. In small amounts it's fine, 10% or so, but not as a major component of a potting mix.