Pumice and lava rock comparison

[KennedyMarx]

How does lava and pumice compare as far as moisture retention, aeration, and CEC? I was thinking of only using one or the other along with akadama for next seasons repotting.

I'm in favor of lava rock just because it looks nicer mixed with akadama than pumice does, but everyone was going crazy about pumice last year after the Hagedorn article on Turface.

 

[edprocoat]

How does lava and pumice compare as far as moisture retention, aeration, and CEC? I was thinking of only using one or the other along with akadama for next seasons repotting.

I'm in favor of lava rock just because it looks nicer mixed with akadama than pumice does, but everyone was going crazy about pumice last year after the Hagedorn article on Turface.

KennedyMarx, if one like Hagedorn or Pall or any of the well know respected names in Bonsai would write an article about the benefits of using motor oil mixed with blacktop as a growing medium , everyone would be crazy about it until they killed a few trees.
I am not saying these guys would ever post anything harmful to Bonsai, just things like this are the next fad when given credence by someone well known.
Personally I do not see much of a difference in pumice or lava, but I always go for lava as its heavier and does not float when watered.

ed

 

[Smoke]

How does lava and pumice compare as far as moisture retention, aeration, and CEC? I was thinking of only using one or the other along with akadama for next seasons repotting.

I'm in favor of lava rock just because it looks nicer mixed with akadama than pumice does, but everyone was going crazy about pumice last year after the Hagedorn article on Turface.

These questions are source of controversy and most often lead to many differences of opinion. There are a few here religious about soil components of which both items you mention. Me as we'll as Adair Brian and few others. Seek out one you trust and ask them by pm and get a solid answer free of all the distractions this group can bring.

 

[yenling83]

How does lava and pumice compare as far as moisture retention, aeration, and CEC? I was thinking of only using one or the other along with akadama for next seasons repotting.

I'm in favor of lava rock just because it looks nicer mixed with akadama than pumice does, but everyone was going crazy about pumice last year after the Hagedorn article on Turface.

Kennedy-
Both lava and pumice have different benefits. Your mix should be in line with the goals for the individual tree. If you have the same particle size, then pumice dries out faster than lava and akadama. I use 100% sifted pumice of medium and large size to establish newly collected conifers. This is because pumice is fantastic at getting really vigorous root and top growth quickly. Once you have an established tree and you start working on refinement you generally don't want your tree growing as fast, which means you want a mix that will stay wet for a longer amount of time. I think you are fine using just lava and akadama or just pumice and akadama. The Lava mix will stay slightly more wet, but not a whole lot more. I've been told that lava helps you to achieve more root divisions than pumice, although not sure if this is true or not. If you want a drier mix, then increase the lava, or add pumice, or increase particle size or put into a smaller container. Good luck!

One of my fav reads on soil.
http://peterteabonsai.wordpress.com/2012/05/15/repotting-a-beast/

 

[markyscott]

That which we call "lava rock" is "scoria" to geologists. Pumice and scoria are both volcanic rocks made from rapidly cooling erupted lava. The holes are formed when the lava quenches with trapped gas bubbles inside. Pumice and scoria are differentiated by density alone - pumice is less dense than water and scoria is more dense. They are both volcanic glass (no or very few minerals). Scoria tends to be more common with more mafic (higher iron and magnesium) volcanoes, but other than that and the density, they are quite similar.

In terms of water retention, I expect there is some variability. But the pumice and scoria I've tested have quite similar water retention and air filled porosity as long as the grain sizes are similar.

Scott

 

[edprocoat]

Kennedy-
Both lava and pumice have different benefits. Your mix should be in line with the goals for the individual tree. If you have the same particle size, then pumice dries out faster than lava and akadama. I use 100% sifted pumice of medium and large size to establish newly collected conifers. This is because pumice is fantastic at getting really vigorous root and top growth quickly. Once you have an established tree and you start working on refinement you generally don't want your tree growing as fast, which means you want a mix that will stay wet for a longer amount of time. I think you are fine using just lava and akadama or just pumice and akadama. The Lava mix will stay slightly more wet, but not a whole lot more. I've been told that lava helps you to achieve more root divisions than pumice, although not sure if this is true or not. If you want a drier mix, then increase the lava, or add pumice, or increase particle size or put into a smaller container. Good luck!

One of my fav reads on soil.
http://peterteabonsai.wordpress.com/2012/05/15/repotting-a-beast/

How does this work ?

ed

 

[Smoke]

I should call myself Nostradamus....

 

[KennedyMarx]

How does this work ?

ed

He meant lava will stay wetter than pumice and in an akadama/lava mix, increase the ratio of lava for a drier mix.

 

[markyscott]

Here are the data. Scoria and pumice, seived to 3/8" particle size and dried. Purchased from Wee Tree in early 2014.

 

[markyscott]

500 ml of each, to which i poured through 500 ml of water. Pumice retained about 25 ml of water, scoria retained about 100 ml.

Scott

 

[markyscott]

Pumice (3/8" grain size)
Porosity = 31%
Air-filled porosity = 26%
Water-filled porosity = 5%

Scoria (3/8" grain size)
Porosity = 40%
Air-filled porosity = 20%
Water-filled porosity = 20%

So, this pumice has lower porosity than scoria, but higher air filled porosity and lower water retention.

Scott

 

[KennedyMarx]

500 ml of each, to which i poured through 500 ml of water. Pumice retained about 25 ml of water, scoria retained about 100 ml.

Scott

Did you not wash and dry the pumice and lava first? Why is the water in te pumice test red?

 

[markyscott]

Did you not wash and dry the pumice and lava first? Why is the water in te pumice test red?

Sorry, the red color is just food coloring. So the water levels can be more easily seen.

Scott

 

[Poink88]

In terms of water retention, I expect there is some variability. But the pumice and scoria I've tested have quite similar water retention and air filled porosity as long as the grain sizes are similar.

Scott

500 ml of each, to which i poured through 500 ml of water. Pumice retained about 25 ml of water, scoria retained about 100 ml.

Scott

Hmm..isn't that statement contradicting your results? 25ml vs 100ml is 4 times more water.

 

[markyscott]

Hmm..isn't that statement contradicting your results? 25ml vs 100ml is 4 times more water.

Yep. More of a difference than I remembered.

Scott

 

[coh]

Hmm, I did a similar test a couple of years ago. Took similar sized pumice (also from wee tree) and red lava (beam clay, from Hollow Creek). Thoroughly dried both, filled a cup, weighed dry, soaked, drained, weighed wet. I found the pumice actually held more water than the lava.

Lava: dry weight 73 grams, wet weight 95 grams, water weight 22 grams (30%)

Pumice: dry weight 65 grams, wet weight 95 grams, water weight 30 grams (46%)

For comparison, turface: dry 73 grams, wet 115 grams, water 42 grams (57%)
For comparison, kanuma: dry 42 grams, wet 72 grams, water 30 grams (71%)

Thought I did akadama, have to see if I can track down those numbers.

Need to repeat the test, as I only did one sample of each.

Chris

 

[wireme]

Sounds like one of you soaked the material and one of you poured it through?
Pumice pores are slower to fill?

 

[coh]

I definitely soaked the materials (left them sitting in a cup of water for quite a while), then drained. Was measuring the total water holding ability, so it is possible that one saturates more quickly than the other. I'll have to look at that next time I do the tests.

Chris

 

[Smoke]

These questions are source of controversy and most often lead to many differences of opinion. There are a few here religious about soil components of which both items you mention. Me as we'll as Adair Brian and few others. Seek out one you trust and ask them by pm and get a solid answer free of all the distractions this group can bring.

Interesting....

 

[markyscott]

Hmm, I did a similar test a couple of years ago. Took similar sized pumice (also from wee tree) and red lava (beam clay, from Hollow Creek). Thoroughly dried both, filled a cup, weighed dry, soaked, drained, weighed wet. I found the pumice actually held more water than the lava.

Lava: dry weight 73 grams, wet weight 95 grams, water weight 22 grams (30%)

Pumice: dry weight 65 grams, wet weight 95 grams, water weight 30 grams (46%)

For comparison, turface: dry 73 grams, wet 115 grams, water 42 grams (57%)
For comparison, kanuma: dry 42 grams, wet 72 grams, water 30 grams (71%)

Thought I did akadama, have to see if I can track down those numbers.

Need to repeat the test, as I only did one sample of each.

Chris

The solution will be highly dependent on the grain size, the sorting, and the container height. As you decrease the grain size, the porosity will stay about the same, but the water filled porosity will increase and the air filled porosity will decrease. Decreasing the container height will have the same effect.

Scott