Soil particle size

[Lannabulls]

Hi,
I mix my soil using generally different % of organic and inorganic ingredients, mainly akadama, kanuma, pumice and lava rocks.
What about inorganic particle size?
I did some reserch, generally speaking I understood why it is better do not mix different sizes however some experts out there suggest bigger size for conifers, smaller for deciduous, etc and francly I dont understand why.
Could you please teach me, how you choose your pumice, lava rock particle size, wich crireria to follow?
Thanks so much!

 

[Leo in N E Illinois]

Particle size - this is critical - the ENTIRE MIX, ALL COMPONENTS MUST BE RELATIVELY UNIFORM. Or in a more reasonable tone, approach uniform. Your organic particles must be in the same size range as your inorganic particles. So if you use 6.0 to 12.0 millimeters particles of coir your perlite or pumice should be 6.0 to 12.0 mm. I routinely sieve my mixes AFTER blending components together. But that is my preference. Key is that all components are in the same size range.

 

[Wulfskaar]

I think that you don't want differing grain sizes because over time, the smaller grains will fill in the cavities in the lower layers of the soil. I'm not exactly sure how large/small grain size affects roots, but I'm sure you wouldn't want a difference in your roots depending on depth.

 

[PA_Penjing]

I use 1/4" size for everything. If I run out, then kifu sized trees get 1/8". Don't have shohin or they would too. Never heard anything about deciduous getting smaller particles but I'm intrigued. Do you remember where you heard this? Also noticed that when I sift my pine bark to 1/4" it looks much larger than the other particles, I guess because the long but thin pieces fall through the sieve sideways. I try really hard not to over think things. But.. then i do

 

[Lannabulls]

Thanks so much to you all!
I get the importance of using the same particle size, soil must be homogeneous as much as possible, the particles must be all the same size for optimal aeration.
My question again which particle size to use, as exp, why use medium size instead of small? I am asking cause I listened videos about bonsai soil, they were youtube videos in italian, "I am italian living in Thailand", it was suggested to use bigger size particles for conifer, smaller for deciduous, it was not explain why and francly I dont understand the reason why. Do you know something about?
Thanks

 

[Lorax7]

A thin layer of water is held onto a particle by Van der Waals forces (electrostatic). So, when you water your bonsai thoroughly, all the particles get a thin coating on the surface. The amount of water that is held on in this hydration layer is proportional to the surface area of the particles. Lava rock is rough, with lots of little pores, so it holds onto more water than a smooth particle of the same size would because the rough surface increases the surface area per particle. Pumice has a surface that is more rough than lava rock, so it has more surface area than a lava rock of the same size and holds more water. Akadama holds onto even more water because it has little tube structures that allow water to penetrate into the interior of the particle as well as clinging to the surface.

The total amount of water held in a given volume of soil is dependent on the total surface area of the particles in that volume. It turns out that if you fill the same volume with smaller particles, the total surface area increases compared to filling it with larger particles. Basically, having greater numbers of particles is the dominant factor in the overall surface area. So, smaller particle size leads to greater water retention in the soil.

What is the big problem for people that grow shohin? They dry out really quickly, so you have to water them a lot, often multiple times a day during the peak heat of summer. They’re constantly at risk of dying from drought. Hmm… if only there were a way to increase the amount of water held per unit soil volume so shohin wouldn’t dry out so quickly, while maintaining air-filled porosity in the soil column…

 

[Lannabulls]

Thanks so much Lorax7,
Your thecnical explaination is a big help and make me understand much more.
Here in Thailand we have a very hot season, 40 c at list for 2 months, "april-may", in years that is not considered particularly hot, then 4 months of rainy season "june-september".
Now that is winter, 20 c min temp at night, 25-30 c on shade during day, I am forced to water at list once a day, imagine in hot season.....
Therefore to find a perfect mix that can stand very hot months and then after, very rainy ones, is crucial.

 

[john blanch]

Small grain size soil is denser than large grain soil. If the soil in both are made with the same mediums, the smaller grain, denser soil will hold more moisture. And be a good soil for deciduous trees with vulnerable leaves.
The larger grain, less dense soil will give quicker drainage and hold less moisture. And be a good soil for coniferous, evergreen trees with more robust needle foliage.
Try to find what other bonsai growers are using with your climate. I'd say that your soil will have to be well structured and the most variable thing will be your frequency of watering.

 

[Lannabulls]

Thanks John,
That explain the above question!
More robust foliage, bigger particle, etc.

 

[PA_Penjing]

Very cool to have someone here from Thailand, hope you stick around

 

[River's Edge]

"My question again which particle size to use, as exp, why use medium size instead of small?"

Welcome to the site. It is not unusual for a generalized comment to create confusion. Guidelines are important but often incomplete!

Other factor's are often considered when selecting particle size.

One is the desired developmental goals for the root structure. For example when developing exposed root style larger particles are used to form stronger thicker roots in the beginning. This is due to the larger pore spaces between particles.

A second consideration is the stage of development the Tree and or root ball is at. Collected trees often adapt better in larger or medium particles while in recovery. Choices can be made to adjust to the situation.

A third consideration is the species and the nature of their root structure. Feeder roots on Pine are very different from feeder roots on Azalea for example.
particle size may be varied to suit the species.

 

[Lannabulls]

Thanks so much to you all for your in depth explainations.