It’s repotting time!
And that means we talk about soil mixes ad nauseum…
I get so many questions about mixes—and what I use—that I figured a post might forestall some of them. My current mix is based on what Mr. Suzuki used, which was a mix weighted to akadama, with the rest being pumice. I’ll first give what we did in Japan, and then offer what I do here.
Mr. Suzuki’s mix:
7 parts Akadama (approx. 1/4″ size and smaller)
3 parts Pumice (same size: 1/4″ and smaller)
For trees that had a bit of root rot, some charcoal was added in the drainage layer.
Now a few refinements. For conifers, we’d sift out the 1/16″ size; for deciduous, we’d leave that smallest particle size in. For both mixes the ‘fines,’ the dust, etc. was sifted out. Results in a bit of sifting, doesn’t it? And no small amount of coughing either. I remember aching arms, too. Suzuki had hundreds of trees.
I have altered these proportions to fit our situation: economics (akadama is expensive here, vs. only $3.00 a bag in Japan).
1 part Akadama
1 part Pumice
1 part Akadama
2 parts Pumice
Lava is a good substitute for pumice, but I prefer pumice for its internal properties (much more gas exchange) and because it is lighter. A big box or pot of lava is a heavy thing.
The solid particles like decomposed granite, sand, rock, etc. are not as good as lava or pumice as they have no internal structure that can hold air.
If desired, a layer of fine (1/8″) akadama/lava may be added to the top 1/2″ for better water retention in that hot upper layer and for looks. The only disadvantage of pumice is that it is white…
These mixes, with akadama as a water-holding particle, works for many different climate zones. I lived in Arizona for five years and used soil mixes with the same akadama content with great results. Now in the Pacific Northwest these same mixes show the same consistency: Strong growth, best ramification of fine feeder roots, and little chance of root-rot.
I love this time of year…