Go to OC Farm Supply and get yourself some 40 lb bags of pumice for about $12 each. Tell them you are a member of the Orange County Bonsai Society and you get a discount.
Go to Green Thumb and get yourself some pine bark micro nuggets. If my memory serves me correctly, they stock both mini and micro sizes - you want the micro. They should be very small pieces - about 1/2" and less.
Add the pine bark to the pumice at about a 10%/90% to 20%/80% blend. Finished!
Avoid adding any potting soil or similar organic product to your bonsai soil that will clog the soil. If you water your bonsai and the water doesn't immediately pass through the top of your soil and flow out through the drain holes (leaving wet soil particles behind) your soil is too dense / clogged.
Sorry to reply to such an old message, I could not find the one I meant to respond to, perhaps on another thread... So is vermiculite at all suitable to add to this mix, as well as small fragment black lava rock? And I've read that the 'water to your heart's desire' approach (and I should add, as I have read, a suitable mix for 'fertilize very aggressively as well') can also include a degree of sphagnum or coir, and/or vermiculite? These are my main questions
If vermiculite is not great to add to this mix for bigger plants, , is it good for first potting many seedlings ready to pot, instead of any kind of soil? I ask because every potted tree I have ordered online has come with a mainly soil mixture, and I am curious why this is the very prevalent practice (eve in one case where a tree came with lots of fine pumice and vermiculite, there was still a good amount of soil) It seems that vermiculite is not more expensive than potting soil, unless these sellers are using plain steer manure for soil, or something along those lines. But they don't seem to, as there is often pumice, perlite, coir, etc. in the mix, and I wonder why they all use soil as well. And please, first questions are more pressing lol
Thanks in advance!