Some facts about bonsai soil

[markyscott]

That is correct, most pumice (at least in Oregon) holds more water than most lava cinders.

It's opposite in the pumice I've tried - specifically that from Wee Tree in Oregon (I don't know what their source is). But it's all very sensitive to particle size, shape, and sorting. You have to sieve carefully to ensure a uniform and equal particle size to measure accurately. Those factors are far more important controls on water retention than than grain composition.

 

[Brian Van Fleet]

Me too...IME, pumice is far drier than scoria.

 

[markyscott]

Here's a little study on one sample. It's not exhaustive, but it is repeatable - at least on that one sample of pumice. If you try different size cuts of the same pumice, it has a much bigger effect than using the same size of different grain composition.

http://bonsaistudygroup.com/general-discussion/substrate-and-water-retention/

 

[coh]

To further complicate things, it seems not all pumice is created equal. I've ordered pumice from weetree, and also from another seller on facebook (can't remember his name right now). They were quite different, the wee tree pumice was much lighter (less dense) than the other, and the water holding capacity was somewhat different. I have to see if I have those numbers around somewhere.

It is difficult to design a good comparison study, though, because as noted - particle size and shape will impact the water holding capacity to some degree. And to compare with turface, you must use similarly sized pieces of lava or pumice...which would be much smaller and more angular than what most use probably use with their "boon type mixes". Still, that probably wouldn't have any impact on the relative water holding capacity of the two ingredients.

 

[sdavis]

To further complicate things, it seems not all pumice is created equal. I've ordered pumice from weetree, and also from another seller on facebook (can't remember his name right now). They were quite different, the wee tree pumice was much lighter (less dense) than the other, and the water holding capacity was somewhat different. I have to see if I have those numbers around somewhere.

It is difficult to design a good comparison study, though, because as noted - particle size and shape will impact the water holding capacity to some degree. And to compare with turface, you must use similarly sized pieces of lava or pumice...which would be much smaller and more angular than what most use probably use with their "boon type mixes". Still, that probably wouldn't have any impact on the relative water holding capacity of the two ingredients.

A good point.
I have attached some more info on this.

 

[Smoke]

I remember reading a while back that you were experimenting with adding pine bark to you mix. Was I just dreaming?

Yes, the experiments have begun.

The real test will begin next week with temps expected to be 106 and better.