Soil shapes and sizes?

At the moment, I have many different types of soils going on. Principally, they are either comprise of pure turface, diatomite and lava, or two of the three, mixed with some additional of bark, peat and/or granite poultry grit. I even have a batch of Turface/grit and composted cow manure that I'm going to try on a tree or two in the near future. Basically, I'm just experimenting to see what gets me the best results. However, I have a lot of questions on my mind. For one thing, Is there an advantage to using several different components of varying shapes and sizes? From my own experience, it seems to create a more aerated substrate than using one product of a uniform shape and size. On the other hand, if you could obtain a planting medium of a spherical shape(like expanded clay pebbles), they should allow for faster drainage and greater air permeability. Size is also an interesting question. I see a lot of people say 1/8-1/4", but using particles as small as 1/16"(I bought a fairly fine turface product a while ago), I haven't seen problems with drainage. Perhaps in a colder climate, people see faster breakdown of the finer particles?

What do you guys think?

Using a range of sizes will result in less open space than one composed of only a single size since the small particles will fit into the gaps between the larger particles. Depending upon the pot size and tree type I use 1/16" - 1/8" (1.6 - 3.2 mm), 1/8" = 1/4" (3.2 - 6.4mm) , or 1/4" - 1/3" (6.4 - 8.5 mm). I sometimes mix a bit of a smaller size into the bulk of a larger size if I want to retain more moisture, but don't want to use 100% of the small size due to having a larger pot.

Round particles will generally have the highest open space. A dense random packing of uniform spheres will fill about 64% of the space leaving 36% open. The theoretical max for packing uniform spheres is 74% if they are in the correct orderly array. Irregular particles that are neither too long nor too flat can pack to higher density if they are properly compacted.

Marty Weiser wrote:Using a range of sizes will result in less open space than one composed of only a single size since the small particles will fit into the gaps between the larger particles. Depending upon the pot size and tree type I use 1/16" - 1/8" (1.6 - 3.2 mm), 1/8" = 1/4" (3.2 - 6.4mm) , or 1/4" - 1/3" (6.4 - 8.5 mm). I sometimes mix a bit of a smaller size into the bulk of a larger size if I want to retain more moisture, but don't want to use 100% of the small size due to having a larger pot.

Round particles will generally have the highest open space. A dense random packing of uniform spheres will fill about 64% of the space leaving 36% open. The theoretical max for packing uniform spheres is 74% if they are in the correct orderly array. Irregular particles that are neither too long nor too flat can pack to higher density if they are properly compacted.

Let me ask you a question. Lets say you have soil mix 1 and soil mix 2. Soil mix 1 uses substrate A, which has a uniform shape and size. Soil mix 2 is 70% substrate A, with the other 30% being substrate B, which is a larger size particle, of a different shape. Are you saying that soil mix 2 would drain more poorly than soil mix 1?

It depends upon several details. In addition, there is drainage versus free space - I was primarily addressing free space. Your second mix is apt to have less free space than the first due to the mix of particle sizes and possibly the shape effect. This may need to less drainage. However, since the smallest of the locally large gaps between particles will be dictated by your smaller, uniform particles I would suspect drainage would be similar, but water retention might be higher since there are more small local gaps due to the tighter packing. Confusing, yes. Unfortunately, the devil is in the details.

A lot of it comes down to ratio of the particle sizes and the volume fraction of the particle sizes. If the smaller particles can fit into the gaps between the larger particles and are present at the right fraction they can fill up a large amount of the space and therefore reduce the drainage. Most of my detailed experience is based upon trying to maximize the packing fraction, but many of the fundamental experiments were done using spherical particles of about the same size range as our bonsai soils. Recently, I have been conducting some experiments with bonsai soil components based upon the same literature, but there is still more work to be done.

With free draining soil mixes based on lava and pumice for instance, regardless of particle size, drainage should not be a problem at all. I would be more concerned with matching the particle size to what I want to achieve following repotting into the new soil mix. Say for instance you want to thicken the trunk you would use a larger particle size, for ramification a smaller size. Obviously this is a generalization.

With free draining soil mixes based on lava and pumice for instance, regardless of particle size, drainage should not be a problem at all. I would be more concerned with matching the particle size to what I want to achieve following repotting into the new soil mix. Say for instance you want to thicken the trunk you would use a larger particle size, for ramification a smaller size. Obviously this is a generalization.

I would beg to differ based upon my data and published concepts. I have tested both lava and pumice (along with several other typical bonsai soil components) and based upon water displacement they both occupy about 42 - 47% (53 - 58% porosity) of the available space with a very slight dependency on the size. Remember that both types of particles are somewhat porous so some of the water is inside what we think of as the particle so the packing fraction is far less than the 68% for a dense random packing of hard spheres (note to self - redo the tests with ball bearings). My particle sizes ranged from 1/16" - 1/8" to 1/3" - 1/2" which covers the typical bonsai soil sizes.

I then punctured the bottoms of the cups following the basic procedure outlined in an International Bonsai article and the very small particles had 25 - 31% porosity after 20 minutes while the largest particles had 40 - 43% porosity. The larger particles drained faster. After 2 days of sitting in the shade in the summer the very small had increased their porosity to 38 - 40% while the largest particles were 48 - 50%. Small particles retained more water. When you consider that roots will more quickly fill gaps in the small particle soil the difference is apt to be larger. However, I do not want to dry out any of my bonsai to get the zero water value to test this hypothesis.

There have also been several articles on water perching that agree with my results - more water is retained at the bottom of a column of fine soil than in a column of coarse soil.

Finally, I agree with the previous author that using a coarse soil to promote fast growth and a finer soil for refinement is a good idea. In a coarse soil the roots have lots of places to roam so they grow quickly which assists with fast top growth. In a finer soil they have to work their way between the particles which slightly slows their growth, but encourages branching as they find their way to moist areas so there is more total root mass. This means there is more root mass to support more leaves and/or needles and finer ramification. On the other hand, if we make the soil too fine (i.e. clay with particles that are 0.001 - 0.005" then the water and air cannot penetrate and the roots will not grow well.

Marty Weiser wrote:I would beg to differ based upon my data and published concepts. I have tested both lava and pumice (along with several other typical bonsai soil components) and based upon water displacement they both occupy about 42 - 47% (53 - 58% porosity) of the available space with a very slight dependency on the size. Remember that both types of particles are somewhat porous so some of the water is inside what we think of as the particle so the packing fraction is far less than the 68% for a dense random packing of hard spheres (note to self - redo the tests with ball bearings). My particle sizes ranged from 1/16" - 1/8" to 1/3" - 1/2" which covers the typical bonsai soil sizes.

I then punctured the bottoms of the cups following the basic procedure outlined in an International Bonsai article and the very small particles had 25 - 31% porosity after 20 minutes while the largest particles had 40 - 43% porosity. The larger particles drained faster. After 2 days of sitting in the shade in the summer the very small had increased their porosity to 38 - 40% while the largest particles were 48 - 50%. Small particles retained more water. When you consider that roots will more quickly fill gaps in the small particle soil the difference is apt to be larger. However, I do not want to dry out any of my bonsai to get the zero water value to test this hypothesis.

There have also been several articles on water perching that agree with my results - more water is retained at the bottom of a column of fine soil than in a column of coarse soil.

Finally, I agree with the previous author that using a coarse soil to promote fast growth and a finer soil for refinement is a good idea. In a coarse soil the roots have lots of places to roam so they grow quickly which assists with fast top growth. In a finer soil they have to work their way between the particles which slightly slows their growth, but encourages branching as they find their way to moist areas so there is more total root mass. This means there is more root mass to support more leaves and/or needles and finer ramification. On the other hand, if we make the soil too fine (i.e. clay with particles that are 0.001 - 0.005" then the water and air cannot penetrate and the roots will not grow well.

I'm testing out different soil sizes on some seedlings that I'm growing. Some are in a substrate that ranges from 1/32"-1/8" and others in in a substrate that ranges from 1/8"-1/4". So far, I have yet to notice any different in growth, but I'll be keeping my eye on them in the next few months to a year.

I thought I would add a few personal observations to this thread. As I've said, I've been trying out several different products. One of them is a Turface product called "All Sport pro." It's a much smaller particle size, and a more reddish color than the MVP/All sport products that most people use. However, the particle size also seems to be much more consistent, around 1/16" or maybe a little smaller. I've used this in several pots have noticed no problems with drainage. Excess waters runs through it like it does with coarse substrates. Additionally, it seems that I can't use a purely inorganic mixture with a particle size much large than 1/8-1/4". I have a few plants in crushed lava in the 1/4-1/3" range, and in full sun they can wilt without. I might try adding some peat this mix to see if changes anything.

PeacefulAres wrote:... a Turface product called "All Sport pro." It's a much smaller particle size, and a more reddish color than the MVP. ...

Ummm. Do you mean "Pro League"?

0soyoung wrote:

PeacefulAres wrote:... a Turface product called "All Sport pro." It's a much smaller particle size, and a more reddish color than the MVP. ...

Ummm. Do you mean "Pro League"?

It could be. The problem is, I get the turface products from John Deere Landscaping and they rename the Turface products. To add to the confusion, they also call the MVP "All Sport." When I first when to buy turface from them, I asked if they had MVP, but they said they carry "All Sport pro," and then said that is was the same thing, but that isn't correct.

Either way, the Pro League is probably what I have. So far, it's been pretty good.