Introductory soil physics

[markyscott]

...It is also long time known that placing a plant in a large mass of soil will often kill it. [ 1970 Canadian garden books ]...

Care to speculate about why this is the case?

...Your question -
Possibly the plant drowns in too much water. Soil is too wet to control. Especially rain and high humidity.

When you up pot a heavily root bound plant, you only move up to a pot so much larger. Depends on the plant,

I'd speculate that this is quite likely the case. In the context of our discussion here, the soils that are used in the nursery trade are typically very fine grained with a high water holding capacity. Because they're so fine grained, the saturated zone at the bottom of the pot can be quite tall - perhaps even above the bottom of the old root ball when they pot up. Without roots in the fresh soil around the rootball, there is no transpiration to reduce the water saturations in this part of the pot, so it stays very high for a very long time. That provides a large water reservoir for capillary action to draw water from and keep the old rootball moist. So it stays damp for a long time, providing an environment conducive to phytophthora and other damaging microorganisms to thrive.

I think that these conclusions are less relevant to bonsai if you avoid fine-grained, high water saturation, low AFP components in your mix.

Scott

 

[markyscott]

OK - back to it. Andrew asked about pumice. What the heck is pumice? And what the heck is lava rock, for that matter? Let's focus on those two soil components.

Pumice and lava rock (I'll henceforth refer to this as scoria) are original volcanic materials. They are not an alteration product like akadama nor are they manufactured like haydite or turface. Pumice and scoria are vesiculated (filled with gas bubbles) volcanic glass - the vesicles that form as the lava is quenched to glass give it it's characteristic high porosity and low density. Here's a side-by-side comparison of pumice and scoria:



Scoria is typically red or black. Pumice is typically white. But this is not the important characteristic. You can have black or red pumice and you can have white scoria, this is just not typical.

What is important is density. Pumice is differentiated from scoria based on density alone. Pumice is less dense than water, scoria is more dense than water. Pumice glass is typically, but not always, a composition geologists describe as felsic - high silicon, aluminum, sodium, and potassium and low magnesium, iron and calcium. Scoria glass is typically, but not always, a composition that is a bit richer in iron and magnesium. Over time, they both will alter into various clay minerals and quartz. The exact alteration pathway depends on the composition of the parent material, the water composition, temperature, pH, and microbial activity. But typically, it breaks down to form various smectitic clays - most often montmorillonite but saponite is common as well (i.e, http://claymin.geoscienceworld.org/content/48/3/423). If it is in contact with alkaline waters and depending on the composition, zeolites can also form (i.e., http://pac.iupac.org/publications/pac/pdf/1980/pdf/5209x2115.pdf).

The density of both pumice and scoria are low because of the vesicles - pumice can be literally filled with them as in this picture:



See? All of those holes were bubbles that evolved from the lava as it ascended through the earth. Just like taking the top off a soda can! When the lava was erupted into the air it was rapidly quenched, freezing those bubbles into place. If the lava was really gassy, it can have a lot of bubbles making it high porosity and low density. If the lava was not gassy, it can have fewer (or none) making it lower porosity and lower density.

Scott

 

[markyscott]

Before I go on about pumice and scoria, I need to introduce a new concept - that of "effective porosity". Effective porosity is described as the fraction of the pore space that is accessible to fluid. In other words, if you have a pore that is completely surrounded by rock - there's no way for the water to access it. The saturation will be zero no matter how big or small the pore space is. And despite the fact that pumice has such high porosity, it's effective porosity is often surprising low! It all depends on how connected the adjacent bubbles are when the lava was erupted. Have a look at this picture:



This is a pumice island. When eruption happen out in the ocean they can produce pumice too. This pumice will float on water - in fact, some pumice can float indefinitely attesting to the fact that very little of the interior pores are connected to the outside of the grain. If they were, water would eventually displace the air, increasing the density of the pumice and the grain would sink.

Scott

 

[Anthony]

Ah, but Mark,

can you say how long the pumice holds out in Bonsai use ?

I would also ask is the Pumice, an Imperfect glass [ pottery science again ] .
Often volcanic materials degrade simply because if you do an oxide testing and then test for glass formation,
the stuff is an imperfect glass and it will fall apart.
If too much alkali / alkaline is coming out it can harm the plant.

There is also the idea that the plants which colonise volcanic flows can handle the above, not necessarily good
for bonsai efforts.

I will continuously ask, is the inorganic stable for a long time [ years ]

Why - because you can design your soil to encourage fine roots and save on having to bare root for
thick root treatment, save with probably extreme age - say over 100 years.
Less work, I am lazy.

The idea is efficiency, the K,I,S,S, of creating a usable soil that promotes HEALTH.

Apologies for being a pest.
Good Day
Anthony

 

[Anthony]

Folks,

as was read on Ausbonsai, and IBC,

I am offering to help Mark so he doesn't end up torturing himself. He is a great guy !!

Your inorganic should be durable under use in the soil. Remember Bonsai is very long term.

[1] We grow our plants for BEAUTY not produce or lumber.

So the demands on the soil is really minimal. [ Fertiliser 12 N and so on ]
[ Big trunk ground grow - apartment try colander in colander with second colander filled with high organic ]

The ball bearing principle -

get a glass cup add marbles observe, sprinkle in a fine organic [ compost / peatmoss etc. ]

This is the idea for freely draining and air. The organic holds the water / fertiliser.

If you could get a porous round fired clay sphere [ we made them ] at say 5 mm or 3 mm.
Life would be easy peasy. Lecca does work, just get that averaged size before mentioned.

The idea is to encourage the plant to keep creating feeder roots.

Come up with an air-pot shape that is bonsai pot shaped and life is even better.

MAYBE a rectangular wire mesh shape that fits say 1 inch shy of the bonsai pot walls for display.

****** if you must grow something as a beginner, grow a native/s to your area first.
Lowers the challenge level for humidity/air temperature / soils /seasons etc.

Grow something from outside your range and you raise the learning difficulty level.

Now get cracking and tap into Mark's knowledge, he is also a Boon student and he will
have tons of specialised information.
Don't force the man to waste his time showing images of floating pumice.
Good Day
Anthony

 

[jacob letoile]

When I took my soils class, for turf management, they talked about the water holding characteristics of soil from a specific view point. In golf courses they organize their soil thusly, a coarse layer on the bottom, and a finer root zone on the top, kind of like what you were talking about for the drainage layer. But the layers were separated by fabric. What they said was this layout could hold more water in the root zone than just a full depth of fine soil, then when it reached a supersaturation point lots of water fell out. Imagine your sponge supported on a screen under a trickle of water. the sponge slowly fills until it reaches saturation and if the water is shut off it will hold that much water, but if you add one more drop a whole bunch of water falls out. This was done to put more water in the root zone with irrigation without running the risk of waterloging in a rain event. If i'm remembering correctly this seems like it could be a useful concept.

 

[wireme]

When I took my soils class, for turf management, they talked about the water holding characteristics of soil from a specific view point. In golf courses they organize their soil thusly, a coarse layer on the bottom, and a finer root zone on the top, kind of like what you were talking about for the drainage layer. But the layers were separated by fabric. What they said was this layout could hold more water in the root zone than just a full depth of fine soil, then when it reached a supersaturation point lots of water fell out. Imagine your sponge supported on a screen under a trickle of water. the sponge slowly fills until it reaches saturation and if the water is shut off it will hold that much water, but if you add one more drop a whole bunch of water falls out. This was done to put more water in the root zone with irrigation without running the risk of waterloging in a rain event. If i'm remembering correctly this seems like it could be a useful concept.

Sounds familiar, like this idea in the text that I took a screenshot of?


It came from this blog post. http://saruyama-bonsai.blogspot.ca/2014/05/books-and-learning.html?m=1

Old text from the 70s copied in the blog, have you looked at that Scott? Still accurate or is some outdated now?

 

[aml1014]

We also haven't talked about the use of wicks in the drainage hole. I've used this technique to reduce the PWT in the soil of plants I aquire out of season and cannot repot.
I know the wicks work because I do use them occasionally but, what is the science behind how they work?

Thanks
Aaron

 

[markyscott]

Sounds familiar, like this idea in the text that I took a screenshot of?
View attachment 119201

It came from this blog post. http://saruyama-bonsai.blogspot.ca/2014/05/books-and-learning.html?m=1

Old text from the 70s copied in the blog, have you looked at that Scott? Still accurate or is some outdated now?

We also haven't talked about the use of wicks in the drainage hole. I've used this technique to reduce the PWT in the soil of plants I aquire out of season and cannot repot.
I know the wicks work because I do use them occasionally but, what is the science behind how they work?

Thanks
Aaron

Aaron / Wireme -

I put these questions together because these are both related concepts. Capillary forces can be unfamiliar to most of us so I'll try to help build some intuition on how this works. It ties together everything we're talking about. We're all familiar with this picture, right?



Water is drawn up the capillary tube against the force of gravity. Why does this happen? This idea has been around a long time - I think that Leonardo da Vinci was the first to describe it. What's going on is this - there is a strong tendency for water to adhere to glass relative to air. It's said that the glass is "water wet". Wetting describes the tendency for a liquid to maintain contact with a solid surface. In the smaller capillary tube there is a large surface area of glass exposed the the liquid relative to the volume of the liquid. So the forces of adhesion are very strong and the water will be drawn a long way up the capillary tube. It will reach the elevation in the tube where the forces of adhesion pulling the liquid up are equal to the force of gravity pulling the liquid down. As the diameter of the capillary tube increases, the surface to volume ratio goes down, so the adhesion goes down as well and the liquid level falls.

Scott

 

[markyscott]

Now imagine that these tubes are interconnected pore spaces in a rock rather than tubes of glass. Well, clearly with the smaller pores water will be drawn a lot further than in larger pores. So let's put that concept in context of the two questions.

Sounds familiar, like this idea in the text that I took a screenshot of?
View attachment 119201

It came from this blog post. http://saruyama-bonsai.blogspot.ca/2014/05/books-and-learning.html?m=1

Old text from the 70s copied in the blog, have you looked at that Scott? Still accurate or is some outdated now?

The statement in the text is exactly accurate. Think about the tubes and what might happen if we have a coarse drainage layer beneath our soil medium. When we water we'll first saturate the bottom of the soil. But we won't spill water across the interface until the weight of the water in the soil overcomes the adhesion between water and soil in the medium. Then it will drain through. So when the text says that water will move with difficulty across the interface, this is what I interpret.

Scott

 

[0soyoung]

Sorry to inject a tangent, but this is how water gets to the top of your trees (and trees you see in the forest).

A leaf above the column is a dead leaf --> height limit of trees. Sequia have very narrow lumens and narrower higher up in the tree than lower/down, for example.

... resuming your regular programming. Had this been a real emergency

 

[markyscott]

When I took my soils class, for turf management, they talked about the water holding characteristics of soil from a specific view point. In golf courses they organize their soil thusly, a coarse layer on the bottom, and a finer root zone on the top, kind of like what you were talking about for the drainage layer. But the layers were separated by fabric. What they said was this layout could hold more water in the root zone than just a full depth of fine soil, then when it reached a supersaturation point lots of water fell out. Imagine your sponge supported on a screen under a trickle of water. the sponge slowly fills until it reaches saturation and if the water is shut off it will hold that much water, but if you add one more drop a whole bunch of water falls out. This was done to put more water in the root zone with irrigation without running the risk of waterloging in a rain event. If i'm remembering correctly this seems like it could be a useful concept.

This is a more difficult question. If I understand it, you're asking what if happens is we put a drainage layer on bottom, cover it with some fabric and put our soil medium on top of that.

I really don't know the answer to this, but what might be happening is that they're trying to reduce the rugosity of the interface. The surface of the coarse drainage layer will be pretty rough if you use coarse grains. When you pour the fine soil on top it will tend to invade the drainage layer to some extent causing variations in height above the drainage layer from point to point across the interface. The water saturation profile in the pot would likely be related to the deepest penetration of fine soil into the drainage layer. However, if you separated the two with a piece of fabric, it would be a smoother layer because the fabric would prevent the fine soil from invading the drainage layer. So higher water saturations would extend higher into the fine soil.

So I think that makes sense.

Scott

 

[markyscott]

Sorry to inject a tangent, but this is how water gets to the top of your trees (and trees you see in the forest).

A leaf above the column is a dead leaf --> height limit of trees. Sequia have very narrow lumens and narrower higher up in the tree than lower/down, for example.

... resuming your regular programming. Had this been a real emergency

Great point Osoyoung. Capillary forces are all around us and more familiar than we might think.



When I was a teenager I didn't have ski pants. I used to just try and Scotchgard my jeans when I went skiing to keep them dry. Didn't work, but that's beside the point. Scotchgard is a chemical treatment that makes a fabric non-wetting. See how the water beads up on the fabric? If it were wetting it would lie flat.

Some plant leaves are nearly perfectly non-wetting. That way the water just rolls off when it rains. Check out this out:


So plant parts are wetting or nonwetting depending on the purpose. Lumens are wetting so that water can be drawn up to support the leaves. But the leaves can be non-wetting so they don't get weighed down by water.

Life is amazing.

Scott

 

[markyscott]

We also haven't talked about the use of wicks in the drainage hole. I've used this technique to reduce the PWT in the soil of plants I aquire out of season and cannot repot.
I know the wicks work because I do use them occasionally but, what is the science behind how they work?

Thanks
Aaron

Wicks -

As a disclaimer, I've never done this myself, but I have no doubt it will work as long as the pores in the soil are finer than the pores in the wick. What will happen is that adhesion will draw water from the reservoir into the wick. The water will be drawn up the wick until adhesion and gravity are in equilibrium. If it encounters a soil with smaller pore throats than the wick, the water will be drawn off the wick and into the soil. If, on the other hand, it encounters a soil with coarser pore throats than the wick, the opposite will happen - the water will be drawn out of the soil and onto the wick.

Scott

 

[markyscott]

...can you say how long the pumice holds out in Bonsai use ?...

Indefinitely. Pumice is a very durable substance. It can last for millions of years in the subsurface without breaking down.

Scott

 

[Adair M]

Sorry to inject a tangent, but this is how water gets to the top of your trees (and trees you see in the forest).

A leaf above the column is a dead leaf --> height limit of trees. Sequia have very narrow lumens and narrower higher up in the tree than lower/down, for example.

... resuming your regular programming. Had this been a real emergency

Oso, I remember a discussion along those lines in school. There's also a concept called "root pressure". Because trees are somehow able to lift water higher than can be explained by capillary forces alone!

I agree with Scott: life is amazing!

 

[fredman]

Scott its interesting to me that pumice has a neutral pH, yet scoria are mostly high (7 - 10) depending where it comes out. How does that happen? (it comes out the same volcano)
I read to rid the scoria of excess lime, it needs to be kept wet outside in the elements for up to 12 mnths. I gather the lime will be in the pores, and are flushed.....?

https://books.google.co.nz/books?id...BFEQ6AEIIDAB#v=onepage&q=ph of scoria&f=false

 

[markyscott]

Scott its interesting to me that pumice has a neutral pH, yet scoria are mostly high (7 - 10) depending where it comes out. How does that happen? (it comes out the same volcano)
I read to rid the scoria of excess lime, it needs to be kept wet outside in the elements for up to 12 mnths. I gather the lime will be in the pores, and are flushed.....?

https://books.google.co.nz/books?id=o9SAQQuZD-EC&pg=PA142&lpg=PA142&dq=ph+of+scoria&source=bl&ots=VwWhjDdj60&sig=27hMyztybTHHykhL3EL8w3Pq7GM&hl=en&sa=X&ved=0ahUKEwi5ltvCjMfPAhWDG5QKHfsmBFEQ6AEIIDAB#v=onepage&q=ph of scoria&f=false

In terms of the statement in the book, I'm guessing that the statement about the excess lime and the high pH are related. Alkaline soils have a high saturation of base cations (K+, Ca2+, Mg2+ and Na+). So if there's excess lime, there's free Ca2+ and the soil is basic.

In terms of why scoria would have excess lime, I'll refer back to something I said earlier - pumice tends to be found in felsic systems whereas scoria is generally found in more mafic systems. Felsic systems tend to be more enriched in K+ and Na+, but they don't break down as fast due to weathering. Mafic systems tend to be more enriched in Ca2+ and Mg2+ and break down more rapidly and are associated with various calcic cements that can be found in the pores.

One thing I don't know is how all of these soil pH measurements relate to bonsai culture. Here's the issue. When we water soil in a garden bed, the soil is fine grained (so there's a large surface area to react) and the water remains in contact with the soil for a long time (days? weeks?). So it has plenty of time to exchange H+ and Al3+ with the grains making up the soil medium that buffer pH. In bonsai culture we tend to use a very coarse grained medium (which reduces surface area) and, during the growing season, we flush many pot volumes of water through the soil every day. In my garden, a given volume of water is in contact with the soil 12-24 hours or less before it's completely flushed out by several more pot volumes of water. I suspect that the pH we should really care is the pH of the water we're using. Does anyone have any thoughts about this?

Scott

 

[coh]

Scott, I think that's some very complex stuff you're touching on in the last post. Most of the research that I've seen is devoted, of course, to standard container culture/mixes and if I recall, the results show that water with high alkalinity can cause a build up of compounds that raise soil pH. I would think you're more up to date on that kind of thing than I am. I have no idea how it would apply to our mostly inorganic "soil" mixes. However, I have seen reports that, for example, the pH of turface can vary widely from batch to batch. What I don't know is, how strong of an effect is that. For instance, rain can be pretty acidic on the pH scale, but since it is weakly buffered (hope I'm getting my chemistry right) its pH can be very quickly and easily altered. So using highly acidic rain for watering might not have much impact on the soil pH. Similarly, maybe turface (and lava) can have relatively high pH but those might be weak effects?

Not sure if I'm conveying my thoughts very well so I'm going to stop...feel free to correct anything I've gotten wrong.

Plus...to measure the pH of a solid like turface or lava, I believe you have to crush it and mix with distilled water. We don't really have that happening in our pots so not sure how relevant those values are?

 

[Adair M]

Hmm...

Since scoria and pumice are essentially glass, and dont dissolve in water, I would think that any pH effects from the dust would get washed out pretty quickly.