Layering substrate by size in a pot...

[markyscott]

I know, thanks
In the summer we got temps mostly in the 90's, rarely gets hotter than 100F, but humidity stays high, so I guess we got that going for us. Still, I think this AFP stuff is very interesting, and I'd love to know more about it!

Liang, J., ZhangJ., and Wong M. H. (1996). Effects of air-filled soil porosity and aeration on the initiation and growth of secondary roots of maize (Zea mays), Plant and Soil v 168, 245-254

Loveday, J. (1974). Methods for Analysis of Irrigated Soils. Technical Communication 54, Commonwealth Bureau of Soils, Harpenden, UK

McGarry (1984), Soil Compaction - Causes and Effect, A Short Review
http://www.regional.org.au/au/roc/1984/roc198425.htm

Wall A. and Heiskanen J. (2009) Soil-water content and air-filled porosity affect height growth of Scots pine in afforested arable land in Finland, Forest Ecology and Management v. 257, 1751-1756

Along with many other papers going back to the early 70s. The generally accepted number is 10% AFP. Below that, oxygen diffusion and root respiration stops and the soil is waterlogged. Growth increases with increasing AFP, but AFP comes at the expense of water in your soil, so you have to water more often.

Scott

 

[MichaelS]

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

Very well written Scott. The only thing I would add is that we (including the Japanese) should stop calling the coarse layer at the bottom of the pot the ''drainage'' layer because of course it has nothing to do with drainage. We should start calling it the ''air'' layer or the ''aerated'' layer or something like that.
After all the real reason for this layer is to have large pore space saturated with water vapour not water....

 

[markyscott]

Very well written Scott. The only thing I would add is that we (including the Japanese) should stop calling the coarse layer at the bottom of the pot the ''drainage'' layer because of course it has nothing to do with drainage. We should start calling it the ''air'' layer or the ''aerated'' layer or something like that.
After all the real reason for this layer is to have large pore space saturated with water vapour not water....

Thank you and you make a really good point. The term "drainage layer" is very misleading and by continuing to use the phrase I probably only add to the confusion. I've written about the effect of the "drainage layer" several times, but I think it remains hard for people to understand. Partly because it's a complicated topic and it's difficult to explain simply in layman's terms and partly because people just want to grow trees and not worry about soil physics. I think as soon as I use the word "capillary" I lose about 90% of the audience.

http://www.bonsainut.com/threads/why-i-dont-use-turface-anymore-with-pics.14560/page-6#post-194156
http://www.bonsainut.com/threads/can-you-overwater-in-mostly-inorganic-soil.10540/#post-134678

Scott

 

[JudyB]

The term "drainage layer" is very misleading

agreed! Most of us think of perched water table when we think of this...

 

[Woodland Spirit]

I use layering and wicking. I don't know why or when I started but I seems to work here in the arid air and hellish heat.

 

[Tentakelaertje]

Liang, J., ZhangJ., and Wong M. H. (1996). Effects of air-filled soil porosity and aeration on the initiation and growth of secondary roots of maize (Zea mays), Plant and Soil v 168, 245-254

Loveday, J. (1974). Methods for Analysis of Irrigated Soils. Technical Communication 54, Commonwealth Bureau of Soils, Harpenden, UK

McGarry (1984), Soil Compaction - Causes and Effect, A Short Review
http://www.regional.org.au/au/roc/1984/roc198425.htm

Wall A. and Heiskanen J. (2009) Soil-water content and air-filled porosity affect height growth of Scots pine in afforested arable land in Finland, Forest Ecology and Management v. 257, 1751-1756

Along with many other papers going back to the early 70s. The generally accepted number is 10% AFP. Below that, oxygen diffusion and root respiration stops and the soil is waterlogged. Growth increases with increasing AFP, but AFP comes at the expense of water in your soil, so you have to water more often.

Scott

Many thanks for explaining! This is going into the 'super-useful-bonsai-stuff' codex.
Do I understand it correctly when I say that the AFP actually is the aeration rate of the soil? Also, if the spaces/'tunnels' between the soil particles are bigger than the maximum size capillary stuff works (by putting larger particles on the bottom), will the perched water table problem be solved, and what does that mean to the lower regions of the rootball/soil? Or am I thinking the wrong way around? Apologies for not being really clear, I'm very tired, but bedtime is not in sight yet...

 

[quietobserver]

Thank you and you make a really good point. The term "drainage layer" is very misleading and by continuing to use the phrase I probably only add to the confusion. I've written about the effect of the "drainage layer" several times, but I think it remains hard for people to understand. Partly because it's a complicated topic and it's difficult to explain simply in layman's terms and partly because people just want to grow trees and not worry about soil physics. I think as soon as I use the word "capillary" I lose about 90% of the audience.

http://www.bonsainut.com/threads/why-i-dont-use-turface-anymore-with-pics.14560/page-6#post-194156
http://www.bonsainut.com/threads/can-you-overwater-in-mostly-inorganic-soil.10540/#post-134678

Scott

I was taught that the purpose of a coarse layer in the bottom of the pot was to ensure proper air flow from below the roots, as well as above the roots. It's a lot like opening windows in your house when there's a breeze outside; if you open a window on both ends of the house you get a nice breeze THROUGH the house that far exceeds just opening a window on one end.

 

[Cadillactaste]

I also do use a "top dressing" of sphagnum moss, or on shohin, sieved fines on the trees during the hottest part of the summer. I just don't really consider that part of the soil mix... but I suppose it could be considered thusly. I had assumed that the idea being put forward here, was of many layers graded all the way from container bottom to top within the mix.
Good explanation @markyscott
I think that anyone looking for the perfect answer in these types of threads is looking for the holy grail. You have to take this information -and your climate, and your watering habits, and your tree type and size, and where it is in it's development...... yada yada yada....

Wanting to make sure I understand what your saying...on the shohin you use the sieved fines. Like in dust particals? I'm thinking my brain is not thinking on the same page as to what you use. But the actual maybe say middle sized seive screen. Which would have smaller particles. (Though in all honesty...I only sifted my substrate through the finest screen to remove the dust particles that clogged my smaller drain holes.)

Of course this is magnified in the close up. The particles are very tiny. . Very fine and soft sieved fines from my Wee Tree soil mix.

Thanks everyone for sharing your experiences...And @markyscott your indepth post also was enlightening.

 

[0soyoung]

The generally accepted number is 10% AFP. Below that, oxygen diffusion and root respiration stops and the soil is waterlogged. Growth increases with increasing AFP, but AFP comes at the expense of water in your soil, so you have to water more often.

This makes me wonder about the effect of a root population on AFP - does the AFP go up with the population of roots in the substrate or go down? With a non-compacting substrate, 'fat' roots can push the particles apart, possibly increasing the AFP; 'thin' roots conceivably could reduce the AFP. If root diameters were the same as the average pore size, AFP wouldn't be affected.

I suspect that AFP increases with root population of Turface MVP (chem fert, no poo). It would be interesting to know but seems inhibitively troublesome to measure with a bonsai.

Have you given any thought to this sort of insanity? Is there a practical way to have an indicator measure, or is 'its draining slowly' or 'the foliage is looking sickly' all there is?

 

[wireme]

This makes me wonder about the effect of a root population on AFP - does the AFP go up with the population of roots in the substrate or go down? With a non-compacting substrate, 'fat' roots can push the particles apart, possibly increasing the AFP; 'thin' roots conceivably could reduce the AFP. If root diameters were the same as the average pore size, AFP wouldn't be affected.

I suspect that AFP increases with root population of Turface MVP (chem fert, no poo). It would be interesting to know but seems inhibitively troublesome to measure with a bonsai.

Have you given any thought to this sort of insanity? Is there a practical way to have an indicator measure, or is 'its draining slowly' or 'the foliage is looking sickly' all there is?

I was thinking similar thoughts, I would expect substantial changes due to root growth and mycorrhizal colonization.
Blocking the drain holes and slowly filling the pot to the rim and test as Scott describes with a measuring cup?

 

[GrimLore]

This thread is borderline funny

Grimmy

 

[Woodland Spirit]

Yep.

There is some good information contained herein though.

 

[markyscott]

I was taught that the purpose of a coarse layer in the bottom of the pot was to ensure proper air flow from below the roots, as well as above the roots. It's a lot like opening windows in your house when there's a breeze outside; if you open a window on both ends of the house you get a nice breeze THROUGH the house that far exceeds just opening a window on one end.

I'm guessing most of the air exchange happens when you water. The drainage layer itself has a higher AFP, but it increases the amount of water in the pores elsewhere in the pot. Your soil has a lower AFP and higher average water saturation due to the "drainage layer". It has the same effect as using a shallower pot.

Scott

 

[quietobserver]

I'm guessing most of the air exchange happens when you water. The drainage layer itself has a higher AFP, but it increases the amount of water in the pores elsewhere in the pot. Your soil has a lower AFP and higher average water saturation due to the "drainage layer". It has the same effect as using a shallower pot.

Scott

I tend to have better luck with water lovers. Splains a lot lol..

 

[0soyoung]

I was thinking similar thoughts, I would expect substantial changes due to root growth and mycorrhizal colonization.
Blocking the drain holes and slowly filling the pot to the rim and test as Scott describes with a measuring cup?

I was thinking water and let drain for a few minutes (until water quits dripping out). Then putty over the pot holes. Pour in measured amount of water. Put over a collection 'tub' and remove putty. Amount of water collected indicates AFP. Do this after repotting for a start point. Repeat at a later time - more recovered = AFP up. Likely should repeat the test several times on each occasion just to verify accuracy/repeatability of the measurement.

I bet poo users will see AFP decline markedly unless it is teabagged.

Advice to water sparingly after repotting could really be because that is when the AFP is minimal ( or equivalently WFP is maximal). Maybe that isn't the case at all. Maybe the magic grain size is the size that leads to no change in AFP with root population?

Little to do with creating bonsai, but I cannot help myself!

 

[Woodland Spirit]

deodamnatus, I think we should complicate simplicity.

 

[Cadillactaste]

I was thinking water and let drain for a few minutes (until water quits dripping out). Then putty over the pot holes. Pour in measured amount of water. Put over a collection 'tub' and remove putty. Amount of water collected indicates AFP. Do this after repotting for a start point. Repeat at a later time - more recovered = AFP up. Likely should repeat the test several times on each occasion just to verify accuracy/repeatability of the measurement.

I bet poo users will see AFP decline markedly unless it is teabagged.

Advice to water sparingly after repotting could really be because that is when the AFP is minimal ( or equivalently WFP is maximal). Maybe that isn't the case at all. Maybe the magic grain size is the size that leads to no change in AFP with root population?

Little to do with creating bonsai, but I cannot help myself!

Some are grasping better than others. I believe my eye is twitching. Lol

I'm interested in doing the larger size substrate as a base this spring. Seems more use the sieves for various situations.

 

[MichaelS]

A couple of points about the perched water table that may have been overlooked.
Firstly a perched water table can only occur if all the particles are solid (like quartz or glass beads for example). Most bonsai soils have particles which are absorbent. Organic, Akadama, Turface, Pumice, etc etc all have microscopic pores within the particle. Therefore if they are in contact with a similar material of much smaller particle size above them, they will continue to draw water down to the bottom of the container and it will drain away until the surface tension of the material itself (not it's particle size) stops further drainage. You could have say 1mm particles of akadama as the main portion of the substrate with a layer of 10mm particles of Akadama or Pumice beneath it and still not have a perched water table forming. So, you can only achieve a perched water table if you use non absorbent material of a larger size at the bottom of the container.
Secondly, because most bonsai media are also of a very large particle size compared to soil, the whole perched water table theory becomes pretty much irrelevant as far as the horticultural significance is concerned.

 

[Cadillactaste]

A couple of points about the perched water table that may have been overlooked.
Firstly a perched water table can only occur if all the particles are solid (like quartz or glass beads for example). Most bonsai soils have particles which are absorbent. Organic, Akadama, Turface, Pumice, etc etc all have microscopic pores within the particle. Therefore if they are in contact with a similar material of much smaller particle size above them, they will continue to draw water down to the bottom of the container and it will drain away until the surface tension of the material itself (not it's particle size) stops further drainage. You could have say 1mm particles of akadama as the main portion of the substrate with a layer of 10mm particles of Akadama or Pumice beneath it and still not have a perched water table forming. So, you can only achieve a perched water table if you use non absorbent material of a larger size at the bottom of the container.
Secondly, because most bonsai soils are also of a very large diameter compared to soil, the whole perched water table theory becomes pretty much irrelevant as far as the horticultural significance is concerned.

Hm-mmm I was thinking @Adair that Boon used just larger particles of his mix for the base. I may have misunderstood. I will go back and read my notes.

 

[Adair M]

Hm-mmm I was thinking @Adair that Boon used just larger particles of his mix for the base. I may have misunderstood. I will go back and read my notes.

If it's a large tree and pot, Boon will place a drainage layer of pumice on the bottom. Most medium to small bonsai it's not needed. Most bonsai get the Main Mix size of soil. Smaller deciduous and shohin trees get the smaller sized mix. Only rarely does he place small soil on top of a regular size main mix. It's is more likely he may put a layer of chopped New Zealand spaghnum moss on top if he feels the tree needs more water.

Really, everyone is WAY overthinking this. Keep it simple.