Over the last 33 years I have tried numerous soil mixes for Bonsai some with good success and some failures, if you haven’t lost a tree to two then you have been lucky, these soils and mixes are based on my own personal experience based on my location in the southern part of England where we can get a lot of rain or a lot of sunshine, the most difficult thing about soil mixes is nobody can predict the weather, I may decided that I will mix my soil providing more drainage for a slightly wetter summer and then get caught out with it being very dry and hot, 2022 has been very dry and hot, next year I could mix soil for hotter weather maybe adding more pine bark for water retention and then it could rain all summer, my mix’s seems to work out pretty well regardless if it’s hot or raining I just have to adjust my watering patten to suit, if it’s dry I might have to water some trees more than others and some every other day.
Back in 1989 when I first started growing bonsai there was no internet and no freely available advice that you can google as you can today, my original mixes that I used were from Harry Tomlinsons Bonsai book, 2 parts grit, 2 parts Irish moss peat and 1 part loam a very organic mix but it worked for me at the time and used this mix for quite a few years.
Now as ideas have changed and good results can been achieved with good quality inorganic mixes and now with more widely available information everybody can try with different mixes some may not workout and providing the tree doesn’t die or deteriorate or may just be struggling the mix can be altered to suit the following year.
Kittydama
I still prefer to use Molar clay but not 100% mix as I find it does dries out very quickly on very hot summer days, it’s not a problem if your at home, retired and have opportunity to water every 3 or 4 hours! Sanicat Pink is now my preferred choice and widely available now sold as KittyFriend also a much better option and grain size of 4-8mm that can be sifted into two sizes if required.
Tesco used to sell non clumping diatomaceous earth cat litter (molar clay) but this has not been available since 2020 when they stopped selling it. The Tesco brand was a very small granular size 2-3mm but it used to dry out super quick, one year as an experiment I repotted a very old Satsuki Azalea in 100% Tesco’s cat litter originally planted in 100% Kanuma there was no noticeable difference in growth that year, roots or flowers between the two substrates apart from the frequent watering!
Molar Clay in my opinion is better when you mix it with other components, for deciduous trees my mix would consist of 70% Molar, 20% Pumice or Lava and 10% fine pine bark and for pines 60% molar, 20% Pumice or lava and 20% pine bark.
One year I planted a European hornbeam in 100% Sanicat pink the tree was wired down in the pot, watered and very heavy to move but I had to move it about a month after repotting, one thing to be aware of that this substrate can land slide if your not careful! I Moved the pot when trying place it on the ground the pot slipped from my right hand and the molar clay decided to part company with the tree roots and pot, this can be very frustrating as the roots were just starting to get established something that does not happen with organic soils as they tend to bond together much better than inorganic soils, unfortunately this can happen with any inorganic soil mix so beware until the roots are fully established and the roots have occupied the whole pot.
Akadama
There’s a lot of controversy on the internet about Kittydama vs Akadama my personal opinion on this will differer to another bonsai enthusiast, some will loath it even though they have never tried it and some will say there trees will grow great planted in it Kittydama, never ask a trader who sells Akadama as they all say it’s rubbish! I remember asking one trader about molar clay his response was “your only watering the cat litter and not the tree!” Well not really true as the Kittydama will hold water and nutrient available to the fine fibrous feeder roots as required.
I use Akadama and also purchased mature trees planted in Akadama, if your buying trees the owner has probably got it in his mind that he was going to sell it anyway and probably it’s been left in the pot for a year or two longer than it should of been, in the UK we never really have long periods of frosts if Akadama is frozen all winter then thawed out this is not really going to be problem because we have so many frost cycles the Akadama will break down very quickly and turn to brown mud, this is something I have found in purchased trees that have been left in Akadama for very long time. Akadama in my opinion is better for mature and very refined trees for greater ramification also providing your going to repot every two years, the difference with Akadama vs Kittydama that the roots can grow into Akadama the Akadama splits and forces the roots to divide creating a much finer root structure, Kittydama does not do this your end up with a thicker dense root structure but this OK if your just growing the tree on in it’s early stages of life but adding pumice or lava to your mix this will help to create a finer root structure.
If I use Akadama I prefer to mix it with pumice and lava at mix of 33% of each substrate, unfortunalty availability and the rising cost it’s just to expensive if you have a lot of trees to repot every two years the benefit of Kittydama mix is that it can be cleaned saved and reused.