Layering substrate by size in a pot...

JudyB said:

I also don't think it's a simple as yes or no, meaning that some use a drainage layer. But what you are talking about here is many layers in differing sizes all the way from the bottom to the top.

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Anthony said:

Waltron,

it is how ball bearings touch each other, and being the same size.
Get a bag of marbles, all the same size.
Observe.
Good Day
Anthony

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Waltron said:

welp maybe you can save me some trouble and share some of your marble experiment data, now I can see the bb to marbles comparison, but how about 2 different kinds of marbles that are 1/4" and 2 different kinds of marble that are 3/16"all mixed together in equal parts, so we have 4 unique marbles, 2 of which are 1/4 rd and 2 of which are 3/16" rd?

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Waltron said:

I do get the marble reference that makes sense, they will hold each other in place creating space for roots to grow, I'm curious though at what point, and to what degree can you sacrifice the particle size in order to capture the beneficial attributes and diversity of various materials in the soil? say you have 4 materials that are exactly the same particle size, that mix is going to be preferred over a mix of all the same material the with the same particle size, right? what seems to be the general consensus in particle size variance before people start to notice negative response from the roots and trees?

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Adair M said:

I think you're missing the point.

In the Main Mix, there s no need for multiple sizes. There's going to be a range, because the seiving that we do is not very precise. Doesn't have to be.

In Japan, akadama is often used as the sole ingredient for pretty much any tree. Here in the US, akadama is pretty expensive because of the cost to ship it. So, we cut it with lava and pumice.

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Waltron said:

im not missing the point, im asking what is that range?

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Waltron said:

im grasping 3/16 to a 1/4 is probably ok, but bbs to marbles are not.. are bb's 1/8"?

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1. Air-filled porosity (the porosity occupied by air right after you've watered it). For nursery plants, good potting mixes have AFP above 10-15%. Plants need a high AFP to grow well - I usually shoot for about 20% or so. Many soils work fine in a nursery pot, but nursery pots are pretty deep - in a shallow bonsai pot you need a coarser soil to get the same AFP. This is why potting soil is fine in a deep pot but won't work well at all in a bonsai pot
2. Water-holding capacity (the porosity occupied by water right after you've watered it). The higher this is, the less you'll have to water. In nurseries, they are looking for something in excess of 40% to cut down on labor. I go lower to get the AFP higher, but I have to water more often.

1. Using smaller grains will not change the porosity much, but the amount of water in the pore space will go WAY UP at the expense of air. So your AFP will drop like a rock. In a deeper pot this may be OK. In a shallow pot it may not.
2. Round grains will have lower porosity than angular grains. As the porosity drops, you'll need bigger grains to keep the AFP high enough.
3. Angular grains will have higher porosity, but the size of the pores are smaller so the amount of water in the pores gets larger.
4. If you don't sieve, it has two effects - the porosity goes down and the amount of water in the pores goes up. So it's a double whammy on your AFP.

Waltron said:

im grasping 3/16 to a 1/4 is probably ok, but bbs to marbles are not.. are bb's 1/8"?

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markyscott said:

I keep telling myself to not get involved with these kind of threads. But here I go again - I'm like an addict and I feel like I'm repeating myself. Maybe that's a sign I don't have much more to contribute to these.

The two most important physical properties of any potting mix are:

1. Air-filled porosity (the porosity occupied by air right after you've watered it). For nursery plants, good potting mixes have AFP above 10-15%. Plants need a high AFP to grow well - I usually shoot for about 20% or so. Many soils work fine in a nursery pot, but nursery pots are pretty deep - in a shallow bonsai pot you need a coarser soil to get the same AFP. This is why potting soil is fine in a deep pot but won't work well at all in a bonsai pot
2. Water-holding capacity (the porosity occupied by water right after you've watered it). The higher this is, the less you'll have to water. In nurseries, they are looking for something in excess of 40% to cut down on labor. I go lower to get the AFP higher, but I have to water more often.

So if you want to know how good your soil is, replicate the conditions you intend to use it (sifted/not sifted, depth of the pot you're using, if you have a drainage layer, etc) and measure the properties above. It's dead easy to do. Here are the instructions:

http://www.bonsainut.com/threads/can-this-work-in-place-of-turface.19998/page-2#post-276185

Your AFP will change depending on the substrate you're using, but the most important factor is grain size, sorting, and shape.

1. Using smaller grains will not change the porosity much, but the amount of water in the pore space will go WAY UP at the expense of air. So your AFP will drop like a rock. In a deeper pot this may be OK. In a shallow pot it may not.
2. Round grains will have lower porosity than angular grains. As the porosity drops, you'll need bigger grains to keep the AFP high enough.
3. Angular grains will have higher porosity, but the size of the pores are smaller so the amount of water in the pores gets larger.
4. If you don't sieve, it has two effects - the porosity goes down and the amount of water in the pores goes up. So it's a double whammy on your AFP.

For me, I use three mesh sizes with hole diameters of 3/8", 1/4", and 1/8" to make two soil grades discarding grains sizes less than 1/8" and greater than 3/8". The drainage layer is the fraction > 3/8". The main soil is 3/8" - 1/4". The top dressing is 1/4" - 1/8". I like having a finer soil on top because this is the part of the soil that dries out the fastest - having a finer soil there will keep it moist longer.

So by way of answer to the question posed by the OP, I have a drainage layer on bottom, my general soil mix in the middle, and the upper 1/2" to inch is finer top dressing. I often put milled sphagnum on top of that. So by my way of thinking, that is graded - I'll answer yes.

Scott

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markyscott said:

I keep telling myself to not get involved with these kind of threads. But here I go again - I'm like an addict and I feel like I'm repeating myself. Maybe that's a sign I don't have much more to contribute to these.

The two most important physical properties of any potting mix are:

1. Air-filled porosity (the porosity occupied by air right after you've watered it). For nursery plants, good potting mixes have AFP above 10-15%. Plants need a high AFP to grow well - I usually shoot for about 20% or so. Many soils work fine in a nursery pot, but nursery pots are pretty deep - in a shallow bonsai pot you need a coarser soil to get the same AFP. This is why potting soil is fine in a deep pot but won't work well at all in a bonsai pot
2. Water-holding capacity (the porosity occupied by water right after you've watered it). The higher this is, the less you'll have to water. In nurseries, they are looking for something in excess of 40% to cut down on labor. I go lower to get the AFP higher, but I have to water more often.

So if you want to know how good your soil is, replicate the conditions you intend to use it (sifted/not sifted, depth of the pot you're using, if you have a drainage layer, etc) and measure the properties above. It's dead easy to do. Here are the instructions:

http://www.bonsainut.com/threads/can-this-work-in-place-of-turface.19998/page-2#post-276185

Your AFP will change depending on the substrate you're using, but the most important factor is grain size, sorting, and shape.

1. Using smaller grains will not change the porosity much, but the amount of water in the pore space will go WAY UP at the expense of air. So your AFP will drop like a rock. In a deeper pot this may be OK. In a shallow pot it may not.
2. Round grains will have lower porosity than angular grains. As the porosity drops, you'll need bigger grains to keep the AFP high enough.
3. Angular grains will have higher porosity, but the size of the pores are smaller so the amount of water in the pores gets larger.
4. If you don't sieve, it has two effects - the porosity goes down and the amount of water in the pores goes up. So it's a double whammy on your AFP.

For me, I use three mesh sizes with hole diameters of 3/8", 1/4", and 1/8" to make two soil grades discarding grains sizes less than 1/8" and greater than 3/8". The drainage layer is the fraction > 3/8". The main soil is 3/8" - 1/4". The top dressing is 1/4" - 1/8". I like having a finer soil on top because this is the part of the soil that dries out the fastest - having a finer soil there will keep it moist longer.

So by way of answer to the question posed by the OP, I have a drainage layer on bottom, my general soil mix in the middle, and the upper 1/2" to inch is finer top dressing. I often put milled sphagnum on top of that. So by my way of thinking, that is graded - I'll answer yes.

Scott

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GroveKeeper said:

Do you worry about the water having trouble penetrating the finer top layer or the finer material eventually working its way into the coarse mix below?

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Tentakelaertje said:

This is gonna be on the wall above my bed. I googled AFP, so I know what the abbreviation stands for (air-filled porosity), but I can't grasp the meaning (yet). Would you please explain this?

Thanks in advance!

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markyscott said:

To be clear, nothing that I said was new or revolutionary. I've worked for nearly 30 years on fluid flow problems in porous media - I have references from horticultural studies going back almost 50 years. What I said is exactly what you would learn in a basic horticulture class on soils in college.

But in the end people do what they want and they sneer at whatever is not what they are already doing. But this is a hobby and I couldn't care less what people use in their pot in their back yard - you can grow your trees in dingleberries, bb's, and marshmallows as far as I'm concerned and if it makes you happy.

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Adair M said:

Also remember that Markyscott lives in Houston, Tx, where it gets very hot in the summer. He needs a more water retentive soil. You, being in the Netherlands may not.

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