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Everyone likes to think they’ve found the perfect soil mixture! I like to hear what that soil mixture is. I like to use a perlite, sphagnum moss, akadama mixture for mine. What do you like?

Akadama
Crushed fired bricks (clay)
Cat Litter ( Diatomaceous earth - DE)
Coarse river sand (Grit)
Pine bark+coal

For the Azaleas and Cammelias, I use Kanuma, with Miracid quarterly.

All sifted to 4/6mm granules.

Awesome. I forgot to to mention that I sometimes put a layer of pumice at the base of my pots for drainage reasons. How does the cat litter work for you?

1) IBE (Indonesian burnt earth - volcanic clay fired in a kiln, alternative to akadama)
2) Pumice
3) Peat moss (premixed with 1/4th pearlite)
4) And sometimes ...a handful of potting soil

This may vary by tree .... sometimes also look for river sand/coarse grains. I also use green moss layer on top to keep the soil from drying out as i live in a 30-35 C tropical climate, and its mostly hot throughout the year

Cat litter
Based on these characteristics I started to look for solutions that were in use. One of the first I found was actually through the website of Harrie Harrington in the UK: bonsai4me. He grows his trees in pure baked diatomous earth. This product is sold in many European countries as a non-clumping cat litter. If you read the packaging it is actually recommended as a soil improvement addition. Note: This is a very specific type of cat litter. Most brands of cat litter are NOT suitable.

After growing everything in pure diatomous earth for some 2 years, I realized it stayed quite wet. In winter the water stored in the granules when frozen produces a number of icepeaks on the granules. And in summer the substrate did not dry out quick enough to stop algea to form. Watering only every other day was not an option: The substrate would be dry b the time I would rewater. Not ideal, unless you can use a sprinkler system on a 36 hours cycle.

Ground pine bark
I started to look for additives that could work. I started with adding ground up pine bark, which helped a bit, but did not make a big difference. I do keep it in there as I am convinced it helps with bacterial colonization. This in turn helps with the breakdown of organic fertilizer pellets. But.. I cannot find any real confirmation that this indeed helps.

Not lava, Expanded shale
Then I looked at lava. But although I could find it at the right size, it was very heavy. Because of the solidity of the material, it warms up very slowly, which in Spring for me is a downside. So I left that track quickly.

So I was still stuck for a solution, when I was buying some construction materials for the renovation of my house. And that is where I came a across a product called expanded shale (In German: Bl?hton). I found them as a product made to level floors, in a good coarseness for the pots. The kernels are broken and sifted to size. This material drains perfectly. Has a large surface area due to the broken nature of it. And dries quickly. This is now the core material of my substrate. On its own it is too dry. So I mix in kitten litter and bark to keep it more evenly moist without having a constantly wet surface area.

When I started out I tried akadama. For me it was too expensive and as I have a lot of warm/cold cycles during winter, it broke down easily.

Later I tried pure crushed zeolite of 4-6 mm size. One of our forum members recommended it. It drains just as I want to, perfect weight in my opinion, but in the summer, it dries too quickly At least for me 3 watering a day is not suitable.

Then I started to search for baked clay materials and found baked diatomaceous earth granules. They use it to pour onto oil spills and other chemicals so it is easier to clean it up. It is 2-4mm particle size. It drains well and holds just enough water. A regular medium sized pot needs watering once every day in the summer, which is perfect for me. On the other hand it is very light, it should weight a bit more. For bigger trees the particle size could be greater as well.

In the future Im going to mix these two and maybe add some pine bark if I find a suitable product.

I also use some charcoal chips to help microflora thrive

Awesome. I must say, I had my doubts about perlite, but it has become a very important part of my soil. Only negative is how light weight it is when watering. So I mix in the pumice to help weigh it down. I actually found that store bought orchid bark mix helps the micro bacteria thrive. It’s a favorite of mine now

This is turning out to be a very helpful thread.

Some people in Brazil swear they use 6mm expanded clay as the only soil component for conifers.
In Portugal it's sold as LECA.
In Brazil as Cinesita.
I have used it in some soil mixes, but not alone.

Very interesting. I often hear about people in my area growing in a 50/50 perlite turface. I want to try it but I’m afraI’d there won’t be enough water retention. What kind of climate are you growing in?