Introductory soil physics

[markyscott]

I find this information on the water retention and oxygen retention properties of different soil ingredients very interesting and have started testing my own ingredients. Just curious how many other people have gone through the process of testing their own bonsai soil mixes.

Sure! Here’s an article written by Brain Heltsely about the subject.

https://fingerlakesbonsai.weebly.com/uploads/3/9/6/3/39634557/abs_vol_48_no_4_brian_heltsley.pdf

Scott

 

[Gary McCarthy]

Sure! Here’s an article written by Brain Heltsely about the subject.

https://fingerlakesbonsai.weebly.com/uploads/3/9/6/3/39634557/abs_vol_48_no_4_brian_heltsley.pdf

Scott

Actually, Brian was the one that initially got me interested in all of this. I was able to hear him talk in person on the subject at our last local bonsai club meeting. The testing method he describes in the article you linked to is what I've been using to test my own soil ingredients.

Just wondering if you, me and Brian are the only ones testing our soil mixes to see if they have the proper water and oxygen retention levels. Or are there other "soil geeks" out there as well

Scott, can I ask what your bonsai soil mix consists of and what the water and oxygen retention levels are? THANKS!

 

[crust]

I have been thinking a lot about soil in my bonsai an over and over have noticed a major dynamic seemingly not considered within the typical analysis--that is the presence of roots in the soil, or maybe even more of a factor, the presence of living, highly ramified transpiring roots throughout the soil or perhaps coarse, less ramified, bottom-dwelling roots. Anyway, its seems to me, through basic observation, the presence of roots in the soil really changes the dynamic of AFP, WHC, physical factors and capillary properties hugely. Is this factor even really considered???

 

[markyscott]

Actually, Brian was the one that initially got me interested in all of this. I was able to hear him talk in person on the subject at our last local bonsai club meeting. The testing method he describes in the article you linked to is what I've been using to test my own soil ingredients.

Just wondering if you, me and Brian are the only ones testing our soil mixes to see if they have the proper water and oxygen retention levels. Or are there other "soil geeks" out there as well

Scott, can I ask what your bonsai soil mix consists of and what the water and oxygen retention levels are? THANKS!

Sure - It’s in this post. I use a mix of equal parts akadama, lava and pumice sieved 1/4” to 3/8”. It has approximately 60% porosity, 40% AFP, and 20% container capacity. So about 33% Sw.

S

 

[markyscott]

I have been thinking a lot about soil in my bonsai an over and over have noticed a major dynamic seemingly not considered within the typical analysis--that is the presence of roots in the soil, or maybe even more of a factor, the presence of living, highly ramified transpiring roots throughout the soil or perhaps coarse, less ramified, bottom-dwelling roots. Anyway, its seems to me, through basic observation, the presence of roots in the soil really changes the dynamic of AFP, WHC, physical factors and capillary properties hugely. Is this factor even really considered???

You’re absolutely right, Crust. All we’ve done here is talk about the state of the soil when you first put it in the container. After that, things get complicated. The pore space gets colonized by roots, the soil particles get broken down, mycorrhizae and other organisms populate the soil, organics matter from fertilization gets caught in the pore throats, and many other factors. So I’d answer your question thus:

1. Yes it’s considered, but it’s awfully tough to measure objectively and there are many semi-independent factors that will make it difficult to provide useful guidance
2. Most of the factors I can think of will likely increase Sw based on the intuition we’ve built in this discussion. I’ve led this discussion with the idea in mind that we can at least know what factors constitutes good starting point for our soil mix. Things will depart from that ideal over time and we’ll eventually have to intervene by repotting to “reset the clock” so to speak. But having a good starting point is better than having a bad one, because things will only likely get worse from there.

Scott

 

[ralf]

A
So what factors impact AFP?

• Grain shape - rounded particles have lower porosity, angular fragments have higher porosity. Higher porosity tends to mean higher AFP and lower water-holding capacity.

Scott

it is exactly opposite, Scott.

 

[markyscott]

it is exactly opposite, Scott.

Sorry, but you are incorrect. Angular grains make for higher porosity. Rounder grains increase permeability. Here are a couple of references:

“Increase of angularity of grain increases porosity”.
http://archives.datapages.com/data/bulletns/1938-43/data/pg/0022/0009/1250/1272.htm

“The angularity markedly effects the packing with a consequent increase in porosity.”
https://books.google.com/books?id=5...Q#v=onepage&q=angularity and porosity&f=false

Scott

 

[crust]

Another thing I have noted lately is that a leading bonsai expert promotes the use of soils (typical bonsai mix) that ranges from 1/16-1/4( what passes through 1/4" and is retained on 1/16") within the same mix, claiming (for instance) junipers relish this finer mix. He clearly is successful with these finer mixes however, at least in the past it was always taught that segregating soil particle size per individual mix was important. What are your thoughts on this?

 

[Gary McCarthy]

Another thing I have noted lately is that a leading bonsai expert promotes the use of soils (typical bonsai mix) that ranges from 1/16-1/4( what passes through 1/4" and is retained on 1/16") within the same mix, claiming (for instance) junipers relish this finer mix. He clearly is successful with these finer mixes however, at least in the past it was always taught that segregating soil particle size per individual mix was important. What are your thoughts on this?

I'm still somewhat new at all this but it's my impression that some people will use a 1/16" to 1/8" particle size for the smaller shohin bonsai, and use 1/8" to 1/4" particle size for larger bonsai.

 

[coh]

Another thing I have noted lately is that a leading bonsai expert promotes the use of soils (typical bonsai mix) that ranges from 1/16-1/4( what passes through 1/4" and is retained on 1/16") within the same mix, claiming (for instance) junipers relish this finer mix. He clearly is successful with these finer mixes however, at least in the past it was always taught that segregating soil particle size per individual mix was important. What are your thoughts on this?

Are you referring to Ryan Neil? He says he sifts out the fines (< 1/16 I think) and the coarse (> 1/4) and uses the remainder, which is a mixture of particles ranging from 1/16 - 1/4 inch (though for some trees he also sifts out the 1/16"). I had always read that if you used such a range of particle sizes, the finer particles would fill the spaces and the result would be a denser/less aerated soil than desired...so you'd ideally want a smaller range of particle sizes.

 

[ralf]

Very interesting reading, Scott. A bit heavy but nice. Happy to learn something new about cement mixtures.

For a soil - the more angular particles you have the more compacted soil you will get as a result. Based on the differencies in the shape of angular particles you will get much higher size variation by sieving . The space between larger angular particles will be filled with the small ones.

http://www.pasiminan.com/a-good-bonsai-matix-soil-part-3/

 

[0soyoung]

compacted

I think we need this term/word to be defined.

A pile of angular particles will be more stable than of spherical ones. Walk on a pile of rounded river stones and one experience how they will easily roll (ball bearings) whereas irregular crushed stones don't. I think this is 'stability' .

Regular garden soil or plain ole dirt can be 'fluffy', but if one stomps on it it will occupy a smaller volume (just like squeezing the air out of the Charmin). I think this is 'compaction'. Turface, pumice, lava, crushed granite, sand, nor glass marbles don't really 'compact', IMHO.

 

[crust]

Are you referring to Ryan Neil? He says he sifts out the fines (< 1/16 I think) and the coarse (> 1/4) and uses the remainder, which is a mixture of particles ranging from 1/16 - 1/4 inch (though for some trees he also sifts out the 1/16"). I had always read that if you used such a range of particle sizes, the finer particles would fill the spaces and the result would be a denser/less aerated soil than desired...so you'd ideally want a smaller range of particle sizes.

This is my understanding of Ryans soil recommendations also: is what passes through 1/4 inch screen and what is retained on 1/16 screen is used for short needle single flush pines and junipers and what passes through 1/4 inch screen and what is retained on 1/8 screen is used for something like a pondo. Anyway, he uses a mixed gradient and includes a fairly small particle size for many trees he refers to the mentality in that he wants a fine root system therefore you need a finer soil. Nick Lenz would always use a finer mix too. His larch mix was what passes through 1/8 inch screen and what is retained on 1/16 inch screen--most of his finished trees were always growing in a fine soil mix.

 

[coh]

Maybe @markyscott or @Adair M can remind us what Boon recommends regarding particle size when repotting (maybe it's already in this thread but I don't have time to search right now). Do they sift to a smaller range of particle sizes, i.e. particle sizes are more similar? Or do they use a wider range like 1/16-1/4 inch? Maybe it varies with tree species.

 

[Adair M]

We use two sizes of Boon Mix. Small for shohin and small conifers, and large for pretty much everything else. The soil should all be a uniform size. This keeps the soil open. Mixing multiple sizes makes thesoil pack. As does using the fines.

I don’t know the screen dimensions, I use the ones that come with the bonsai soil sifting kit.

 

[wireme]

I have been thinking a lot about soil in my bonsai an over and over have noticed a major dynamic seemingly not considered within the typical analysis--that is the presence of roots in the soil, or maybe even more of a factor, the presence of living, highly ramified transpiring roots throughout the soil or perhaps coarse, less ramified, bottom-dwelling roots. Anyway, its seems to me, through basic observation, the presence of roots in the soil really changes the dynamic of AFP, WHC, physical factors and capillary properties hugely. Is this factor even really considered???

I think about that too quite often. I have a tendency to water recently transplanted trees more than established ones. Usually it seems people advise the opposite. It has just always seemed to me that fresh empty soil doesn't hold onto water for as long as soil occupied by roots. I realize that active roots and transpiration play a role too but still.. I water newly potted things often and heavily even newly collected and potted yamadori, seems to work.
I've also commented before on the seeming ability of a tree and its associated microbes to adapt a substrate to their own advantage sometimes. For example I have planted spruce and RMJ into identical mixes and noticed that very shortly (maybe 3 weeks) the spruce substrate becomes fully colonized by dense visible ectomycorrhizae and the junipers do not. The result is a much more moisture retentive environment for the spruce with exactly the same substrate to begin with.

 

[ralf]

Turface, pumice, lava, crushed granite, sand, nor glass marbles don't really 'compact', IMHO.

AGREE

The graphics (last third of page 2) used to describe the relation between shape of particles and porosity is for me misleading. The angular items are in the shape of crushed stones that will get more compacted=occupy less volume.

 

[markyscott]

AGREE

The graphics (last third of page 2) used to describe the relation between shape of particles and porosity is for me misleading. The angular items are in the shape of crushed stones that will get more compacted=occupy less volume.

It’s a common misconception, but the relationships in the figure are well established. All else being equal, angular grains have a higher porosity but smaller pore size, hence the lower permeability and higher average water saturation. The term compaction describes the loss of porosity over time due to application of an external load. Hope that helps you understand the figure better.

Scott

 

[ralf]

• Grain shape - rounded particles have lower porosity, angular fragments have higher porosity. Higher porosity tends to mean higher AFP and lower water-holding capacity.
• ...angular grains have a higher porosity but smaller pore size, hence the lower permeability and higher average water saturation

Well, this must be my english then.

Nevertheless I am happy that you have switched from "angular fragments " to "angular grain".

 

[markyscott]

• Grain shape - rounded particles have lower porosity, angular fragments have higher porosity. Higher porosity tends to mean higher AFP and lower water-holding capacity.
• ...angular grains have a higher porosity but smaller pore size, hence the lower permeability and higher average water saturation

Well, this must be my english then.

Nevertheless I am happy that you have switched from "angular fragments " to "angular grain".

I understand where your confusion comes from. My apologies. Although both points are correct, my original statement is misleading as written. Please accept this as a correction:

Grain shape - rounded particles have lower porosity, angular grains have higher porosity. Although in general higher porosity tends to mean higher AFP, angular grains have a smaller pore size, hence the lower permeability and higher average water saturation

Thanks for pointing me to a much needed clarification.

Scott