Akadama Clay and water retention

[James H]

I recently purchased four trees from a guy on my local Craigslist. The soil mix that he used seems to drain very well and still retain a lot of moisture. From looking at it, it seems to be a mix of fine gravel, soil and some sort of clay. I have never seen akadama up close so I am wondering if akadama holds moisture well. He seemed to have done a bit of his homework with the bonsai hobby from the brief discussion that we had when I picked them up. So I could see him getting akadama or some other clay sub straight from Dallas bonsai or another online score. Just wondering your guys thoughts on this.

 

[markyscott]

I recently purchased four trees from a guy on my local Craigslist. The soil mix that he used seems to drain very well and still retain a lot of moisture. From looking at it, it seems to be a mix of fine gravel, soil and some sort of clay. I have never seen akadama up close so I am wondering if akadama holds moisture well. He seemed to have done a bit of his homework with the bonsai hobby from the brief discussion that we had when I picked them up. So I could see him getting akadama or some other clay sub straight from Dallas bonsai or another online score. Just wondering your guys thoughts on this.

Are you asking if what you have IS akadama or IF akadama holds a lot of water? If the former, it holds more water than many inorganic soil components, less than some, but grain size and sorting makes a bigger difference. If the latter, post a picture and we can let you know.

Scott

 

[JudyB]

Can't you just ask the guy? Seems like the easy way to know for sure...

 

[Neli]

I have noticed that akadama starts breaking down after couple of years...and yes it holds water well

 

[James H]

Thanks for the replies guys. I was asking if akadama does hold moisture well as the soil that my trees are in that I bought stays moist for what seems like a very long time. I wish that I could contact him but all that I had was the emails through craigslist and I deleted them after picking up the trees, and the post was also deleted.

 

[markyscott]

Thanks for the replies guys. I was asking if akadama does hold moisture well as the soil that my trees are in that I bought stays moist for what seems like a very long time. I wish that I could contact him but all that I had was the emails through craigslist and I deleted them after picking up the trees, and the post was also deleted.

For the same grain size, akadama retains more water than lava and pumice, a similar amount to turface, and less than seramis (no longer available in the US, it seems). This is partly due to what the grain is made of and partly due to its shape. Water retention increases dramatically as grain size decreases and if you don't sieve your soil. Chemical properties aside, water retention is not the only physical measure of a good soil. The other, arguably more important, measure is the air-filled porosity. Good potting soils generally have an air-filled porosity (the volume of the soil occupied by air after you water and the gravitational water drains away) of 15-20% and a water-holding capacity (the volume of the soil occupied by water after you water and the gravitational water drains away) of 25-30%. These values are pretty easy to achieve in a deep container, but much more difficult in a shallow bonsai pot.

Here's one way to measure (you'll need two graduated cylinders or measuring cups to do this - cylinders are much higher precision).

1. Drill a small hole in the bottom of the measuring cup.
2. Fill the cup with a volume of soil to a level about the depth of your pot.
3. Plug the hole on the bottom of the cup.
4. Pour water into the container, filling it to the soil level. The amount of water that you pour in is the total porosity.
5. Now, unplug the hole and measure the amount of water that drains away. This is the air-filled porosity.
6. Total porosity - air-filled porosity is water holding capacity.

It's really easy to do and anyone can check the physical properties of whatever soil mix they wish to use. Since the density of water is just 1 g/cc, you can also use weights if you like. As long as the number fall into the range for the depth pot you wish to use, it should be ok to work with the mix you choose from a physical properties perspective. I think you'll find that grain size and sorting are far more important than grain composition and that it's much easier to get the numbers to work in deeper pots than shallow ones.

Also, as others have mentioned, some soil components can break down over time, roots will grow though the mix (hopefully), fertilization will introduce fines that can clog the works, and so these values will change over time. And there are various chemical measures of soil quality - these generally measure the soils ability to buffer pH and the concentration of various cations and anions in the pore water. Akadama has some unique chemical properties.

Scott

 

[Adair M]

Akadama does break down over time. That is one of it's virtues! As root systems develop, and foliage mass increases, more roots are needed to sustain the foliage. When a tree is repotted, what we want immediately is coarse root growth. An open substrate allow this. Quick root growth.

As time progresses, we generally want to have finer roots develop. This requires smaller particles in the substrate. Akadama breaking down produces these smaller particles. Also, as noted, since smaller particles hold more water, as the foliage mass increases and demands more water, the akadama in smaller particles holds more water.

Really, akadama is magic stuff. It is the perfect medium for growing trees in containers.

Now, after a time, the sheer volume of roots eventually overwhelms the substrate, and it's time to repot. How often repotting is required depends on a lot of factors.

There are many threads on this forum about akadama.