Thirsty Trees, more akadama?

Why is it that when dealing with trees that require more moisture we increase the akadama and not the pumice? i.e. fir, hemlock, and spruce? Isn’t the purpose of pumice to hold h2o? I realize that akadama retains moisture too, i just keep thinking about pumice. We use it when collecting yamadori right? Just trying to understand.

If your goal is providing the tree with water, then yeah increasing pumice is the way to go.

If you also want to scale the root system in the container and get it more ramified, akadama is the soil that will do both.


I’m not sure, but my hunch is that because akadama is made of clay, it is more absorbent than pumice, which although porous, will hold water on its outer surface?
I am about to repot a willow from a multipurpose compost and plan to experiment with adding Fuller’s earth (cat litter) to akadama to increase water holding properties. The tree is in development, and willow likes it wet.

Be careful with cat litter, some do become a sludgy mess.
Also if the akadama isn’t high quality, then you have a real mess in your container.
If you can easily crumble a grain of akadama between your finger, it is not high quality.

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Your correct that in a 1:1:1 mix pumice is the water holding component that doesn’t break down. Pumic is used for Yamadori as it provides the best balance of water and oxygen to assist with the trees recovery.

The reason we used more akadama for “thirsty trees” is because it will self scale with the roots, therefore expanding the surface area in which water is available. Simply put, it will turn into small particle size over time and small particle size means a high water retention. Pumice doesn’t scale with the roots in this way.

thank you all for your input. I appreciate it!