AusBonsai

Yes Deemon I agree in fact I think you are right on the money. I don't think a coarse layer is essential and possibly in certain circumstanced even detrimental, but it does seem it could be very useful in certain circumstances one of the most obvious seems the growing on stage.
Thinking last night I now consider if I may be wrong and the guy that wrote this article is actually correct and a coarse layer may result in the pot holding more water. It seems that a pot of the same diameter but shorter will in effect hold more water in the medium but I am still unsure?
We know that the size of the pot we use can be very important as if the pot is too large then it takes too long for the tree to use the stored water up. I had given this some thought and considered that surely in a larger pot when growing out you could compensate by using a much coarser mix.
Also with the modern substrates that are available to us I believe it is possible to create a mix that is at the optimum water air ratio straight after watering so in theory we could use an over sized pot and just water by a schedule to refresh the water and gas held in the mix(so it does not go stale) with no concern that the water ratio is too high!
I guess many have heard the theory that a coarse mix results in coarse growth and fine mix the opposite. Is this true? Also as a finer grade medium equates to a larger surface area for the roots so using a larger pot with a coarser mix in theory may end up giving the same surface are in the medium for the roots to grow on as using a smaller pot with a finer grade medium. So maybe it is just good practice to get the grade right and use the appropriate size pot?

I read that Olive prefer a finer grade soil so again species could be another variable. Now my head is starting to hurt
All this is why I suggested to Jamie that we can't really conclude anything from what we understand so far! Although I liked his thinking
Like I said I have an olive (bubble leaf) and although it looks healthy it has grown very little. The medium was annoyingly slow to dry out and would then dry suddenly. I took it out of the pot and found there had been little growth of the roots and the resulting water on the bottom of the pot was not desirable.
I am very unsure as to the characteristics of this species(any other tree would have filled the pot with roots in no time) and would normally of put it is a smaller pot so there was less chance of it sitting in water with little root growth. But after reading this article I figured I could manipulate the water table essentially giving my self a much smaller water holding area while still allowing the tree lots of room for root growth to grow out.
I can't say the tree has excelled in growth since which is not surprising at this time of the year but I am now much happier in the predictable way the soil drys and there is still plenty of room for roots if it takes off, so I will have to wait and see what happens when it warms up again.

I try to aviod bring Walter up too much but a Master that puts himself out ther as much as he does is very educational

Hi Paul. I am some what confused by the terms you use and am not sure you understand what I suggest. I will start a new thread to discuss it as it is pretty far off topic

"The best environment is a soil that dries out daily. The best potting practice is to shift to the next larger size pot after each time the plant becomes root established as evidenced by forming an intact rootball. UC Davis studies have shown this, and I have conducted my own studies with Acer palmatum, which have verified it to my own satisfaction. It is not a marginal effect; the resulting growth improvement is significant. "
Brent Walston

I reckon that is on the money.

So Far Hugh Grant and Handy Mick, you two are the closest. The purpose of a drainage layer is to create a space in a soil profile to enable water to percolate VERTICALLY through the denser (finer particle) layers above, into the drainage layer (coarse particle) which allows water to easily move HORIZONTALLY with minimum resistance (and often down a graded slope when in the landscape) to the drainage point, which in a bonsai pot is of course the drainage hole.

Hope this helps.

Cheers,
Mojo

Mojo Moyogi wrote:So Far Hugh Grant and Handy Mick, you two are the closest. The purpose of a drainage layer is to create a space in a soil profile to enable water to percolate VERTICALLY through the denser (finer particle) layers above, into the drainage layer (coarse particle) which allows water to easily move HORIZONTALLY with minimum resistance (and often down a graded slope when in the landscape) to the drainage point, which in a bonsai pot is of course the drainage hole.

Hope this helps.

Cheers,
Mojo

Yep,

That sounds about spot on. As I wondered would it also do some slight air pruning of the roots as well?

Grant

Pot Size.

Ok ;if the so called drainage layer actually allows the pot to hold more water then would it be possible/preferable to go to a smaller pot? The Japanese say a lot of our trees are over potted.

Grant

Grant Bowie wrote:

Mojo Moyogi wrote:So Far Hugh Grant and Handy Mick, you two are the closest. The purpose of a drainage layer is to create a space in a soil profile to enable water to percolate VERTICALLY through the denser (finer particle) layers above, into the drainage layer (coarse particle) which allows water to easily move HORIZONTALLY with minimum resistance (and often down a graded slope when in the landscape) to the drainage point, which in a bonsai pot is of course the drainage hole.

Hope this helps.

Cheers,
Mojo

Yep,

That sounds about spot on. As I wondered would it also do some slight air pruning of the roots as well?

Grant

But the driange layer actauly stops the water leaving the higher section of the pot?

Grant Bowie wrote:Pot Size.

Ok ;if the so called drainage layer actually allows the pot to hold more water then would it be possible/preferable to go to a smaller pot? The Japanese say a lot of our trees are over potted.

Grant

I'm not sure it does hold more water that is the question I still have?
Take these two drawings as two pots of the same width but different height.

The article suggest the shorter pot will hold more water by surface tension. Is this correct?

Same surface area at the bottom in both pots, therefore same water holding at the bottom, but if the soil is moist all the way through in both pots then the pot that holds more soil therefore holds more water.

Grant

Bretts wrote:

Grant Bowie wrote:

Mojo Moyogi wrote:So Far Hugh Grant and Handy Mick, you two are the closest. The purpose of a drainage layer is to create a space in a soil profile to enable water to percolate VERTICALLY through the denser (finer particle) layers above, into the drainage layer (coarse particle) which allows water to easily move HORIZONTALLY with minimum resistance (and often down a graded slope when in the landscape) to the drainage point, which in a bonsai pot is of course the drainage hole.

Hope this helps.

Cheers,
Mojo

Yep,

That sounds about spot on. As I wondered would it also do some slight air pruning of the roots as well?

Grant

But the driange layer actauly stops the water leaving the higher section of the pot?

Gravity will drain out of the higher section what surface tension wont hold; then the water can run easilly sideways to the drainage holes.

That would be the obvious answer Grant and what I thought was correct. But these two statements from the two articles suggest we ae wrong!
It suggest even though the shorter container has less volume if the diameter of the pots is the same the shorter pot will actually retain more water

Although this article has made reference to the use of "drainage layers", it was written to debunk the "drainage myth" and to provide evidence that the addition of a drainage layer in the bottom of a container does not improve drainage, but merely increases the height of the saturation zone in any given container/bonsai pot and in turn, increases the water carrying capacity of the substrate rather than decreasing it. In other words, the same pot without a drainage layer will hold less water because of the height of the column of water prior to the impermeable layer (the bottom of the pot). In closing, I hope I was able to shed some light on what transpires below the surface in a bonsai pot.

I have read this over and over and although it is kinda working from the opposite direction I am sure they are saying the same as the above quote from the first article!

Drainage is affected by the height of the container. Containers that have identical heights but different diameters have similar drainage characteristics when the same media is used in both. In general, water retention of container media decreases as the height of the water column increases. Media in a tall container characterized by a greater depth drains more readily than the same media in a short container with a shallower media depth. Media in a short container remains wetter than the same media in a tall container because of a lack of drainage; use a deeper container to improve media drainage.

Grant Bowie wrote:
Gravity will drain out of the higher section what surface tension wont hold; then the water can run easilly sideways to the drainage holes.

Yes But First Mojo suggests that

The purpose of a drainage layer is to create a space in a soil profile to enable water to percolate VERTICALLY through the denser (finer particle) layers above, into the drainage layer (coarse particle)

If the bottom layer was the same as the rest this would enable the water to percolate vertically! The coarse layer creates water tension above itself which is actually the opposite of what I understand Mojo to be saying!

Shallower containers that hold the same volune of media as deeper pots, have a larger surface area of soil. Surface tension in shallow pots is greater because there is a higher surface area. Drainage, or more accurately water percolation is therefore slowed more by surface tension than in a deeper pot.

Having said that, Shallower pots, with their comparively larger surface area per volume of soil when compared to deeper pots, are more succeptible to moisture loss through evaporation and have less insulation against temperature change.


By the way, what is this article that keeps getting refered to?

Cheers,
Mojo

Bretts wrote:

Grant Bowie wrote:
Gravity will drain out of the higher section what surface tension wont hold; then the water can run easilly sideways to the drainage holes.

Yes But First Mojo suggests that

The purpose of a drainage layer is to create a space in a soil profile to enable water to percolate VERTICALLY through the denser (finer particle) layers above, into the drainage layer (coarse particle)

If the bottom layer was the same as the rest this would enable the water to percolate vertically! The coarse layer creates water tension above itself which is actually the opposite of what I understand Mojo to be saying!

I'm not sure what you are asking here. You don't think that water can percolate vertically through the base of the pot, which is impervious? The drainage principle I described a couple of posts ago is the same regardless of the porosity of media used. The drainage layer does not facilitate drainage, the hole in the pot does. The drainage layer speeds up drainage.

Mojo

Ok, I found the article. Reading it now. It may well be BS.

Mojo

Water in a potting mix is subjected to a couple of forces. There is surface tension which attracts water to a surface. There is gravity which gives water weight. Surface tension will prevent water from draining from a small pore to a large pore. This is a fact. A pore will only drain when the weight of water above it is greater than the force of surface tension which holds it in the pore.

The drain hole in a bonsai pot is essentially the edge of one gigantic pore called the outside world. If you have a potting mixes of small particles, the smaller the resultant pores, the less tendency to drain due to high surface tension forces. Since the edge of the drain hole is a large pore, water is reluctant to drain from the potting mix. So the bottom of the potting mix is always saturated as there is not enough weight of water to push it out of the pot. If you had a glass pot and filled it with mix, you will see that the bottom is saturated up to a height and then large pores will be filled with air, as you rise up further from the bottom the pores with water will be smaller and smaller. If you take a shallow glass pot and filled it with the same mix, saturated it, drained and then placed it next to the first glass pot, you will see that the degree of saturation are exactly the same in both mixes at the same heights. Taking this to bonsai pots, a shallow pot the potting mix is more saturated, but it is the same amount of saturation as a deep pot for the same height of mix.

The gravel layer simply lifts the finer potting mix off the bottom of the pot. The course gravel consist or large pores, so the smaller pores of the finer potting mix do not drain, thus we have a perched saturated zone. The reduced height of potting mix (because of the gravel) makes for a thinner layer, so it drains less. The course mix on the bottom empties due to the larger sized pores, air enters it form the drainage holes, not from the potting mix above, it will have some water retained where particles meet each other and form a small pore . If a pot is ten centimeters deep, and you put 3cm of course gravel on the bottom, the 7cm of fine mix will have the same amount of water in it as the bottom 7 cm of potting mix if the pot didn't have any gravel. 10 cm of fine mix will have more water than 7cm of fine mix simply because it is deeper, but the water content at the bottom 7 cm’s is the same.

Water always travels vertically until it meets some kind of boundary, either a pore size change or the bottom of the pot, it then pools until it can spill over an edge, or the weight of water above forces it through the boundary.

Paul