Soil again, but I think I reasoned it out.

As the mind churns,

compost plus inorganic [ porous or no ]

Compost is a well decayed organic material and it should be dark and unrecognizable particle wise.

Chopped bark, leaf mould, peatmoss, and so on are not decayed, and will try to decompose, losing a great deal of mass.

In a mix of organic and inorganic, non-decayed materials will collapse and lose structure. Become mushy and possibly waterlog, lose air spaces or drain poorly or both.

With compost, and inorganic materials, the loss of organic material is slower, and gives roots time to shift things around.
What I have observed is roots lifting the tree/shrub out of the pot.
Fine particles of organic material, are washed out and do not simply sit on the pot's internal bottom and collect.

As I suggested earlier elsewhere, perhaps, instead of chopped bark one could try a smaller % of those hydrating marbles sold in the florists' shops.
I am also seeing a micro version for keeping soil more moist for longer.

Anyhow, if what I have typed can be proven scientifically, we can then say the problem was never the organic part, but the fact that it was never compost.
Later.
Khaimraj

"Fine particles of organic material, are washed out and do not simply sit on the pot's internal bottom and collect."

Not sure if I go along with this statement. I have certainly had my drainage hole screens clog in the past. Several factors come into play. If, when watering, a smaller volume of liquid is applied to the soil it is possible that not enough velocity is created by gravity and/or soil texture to allow fine particles to be washed through the screens. And roots also play a role in what can get to the drainage holes.

Is compost not simply a matter of degree of decomposition, as opposed to it is or is not?

lordy wrote: it is possible that not enough velocity is created by gravity and/or soil texture to allow fine particles to be washed through the screens.

You are correct. And in container horticulture this effect is dictated by what is know as the soils capillarity. This is a physical property of growing media that dictates where the saturation zone of any container resides after water has been applied. The greater the soil particle size the lower down in the pot the saturation zone will be.

In this "zone" the pull of gravity is unable to overcome the attractive force of capillarity between the soil particles and the surrounding soil water and the soil remains saturated until it either evaporates through the surface of the media or is taken up by the roots of the plant.

This is why fine particles that are less dense then water and are easily suspended in solution collect at the bottom of our pots. They are deposited and remain in this layer unless a force greater then that of gravity and the capillarity of the soil particles (like a strong jet of water aimed directly downward) forces them out.

Ohio state university has an interesting .pdf that touches on a few of these concepts.
http://ohioline.osu.edu/hyg-fact/1000/1251.html

-Jay

drgonzo wrote:

This is why fine particles that are less dense then water and are easily suspended in solution collect at the bottom of our pots. They are deposited and remain in this layer unless a force greater then that of gravity and the capillarity of the soil particles (like a strong jet of water aimed directly downward) forces them out.

This dovetails into another thread recently about the need to sift bonsai soil or not. One poster said that the dust will simply wash thru the drainage holes. I have never taken that route. When I sift, the last step for me is to wash it in a bucket to remove most of the dust. The last step of potting is when I soak the pot/roots/soil with a healthy amount of clean water and keep at it until what comes out is also clean. Washing in the bucket before potting may seem an unnecessary step, but what I pour out of the bucket before potting ALSO came out clean when I was done that step. Some of the dust just clings to the larger particles unless you have some sort of pressurized approach (I do that into the bucket with the hose).

I was playing around with Kanuma earlier this year and had to do a re-pot to place the tree into a larger container. Even though I had sifted the Kanuma before using it, I was impressed by the yellow sludge layer I found lining both the sides and bottom of the pot.

Kanuma sludge.
-Jay

So I took a walk to the plant shop to see -

Soil Moist Plant Paks Plus [ plus fertilizer ] at 9/3/6 but you have to use the conversion formula to get the NPK]

Pre- measured water-storing granules feeds 8-9 months.

My idea was already reality.
Now to test.
Later.
Khaimraj

drgonzo wrote:I was playing around with Kanuma earlier this year and had to do a re-pot to place the tree into a larger container. Even though I had sifted the Kanuma before using it, I was impressed by the yellow sludge layer I found lining both the sides and bottom of the pot.

Kanuma sludge.
-Jay

I'm not surprised. I don't think you can ever sift out all of the fines and dust, especially since the very act of sifting creates more of the dust...as does the soil mixing and potting process. Then there is the gradual breakdown that occurs in the pot.

Did the kanuma sludge seem to impede the drainage? Was this tree potted in pure kanuma or a mixture of kanuma and other components?

coh wrote:
Did the kanuma sludge seem to impede the drainage? Was this tree potted in pure kanuma or a mixture of kanuma and other components?

This was a cutting from my Japanese Beech that rooted well in pure Kanuma and needed transplant. I had only used small window screening at the bottom of the 4 inch nursery pot, but the walls and sides of the container were well caked with Kanuma, as was some of the screen holes.

Best
-Jay