Hey Baja, great idea with this thread!
So over a course of about 10yrs I have kinda figured out what works for me. Background I worked at a bonsai studio for 4-5 years as an apprentice when I was young and that weighed heavily on how I prefer to grow in relating to soil. I have grown everything from trees to caudiciforms and succulents in 100% stone aggregate and had amazing results but daily attention required.
This works very well for me but may. It for all, but this mix allows me to push growth a little faster through very regular fertilization and watering. The theory behind this is that if the soil drains extremely fast I can fertilize just about every time I water which may be a few times a week, without any excess build up happening by being tightly attached to organic matter that holds nutrients much better than my mix which is mostly aggregate. I've never had any fertilizer related problems in this mix!!
This mix is also so fast draining that I almost never have problems with root rot happening during the dormant months. So even if they get a little bit of water while they are shut down the soil doesn't stay wet for long and they don't develop any fungal issues.
I'll give My standard for succulents, cacti, and caudiciforms is about only 25% organics, this is just a jumping off point because depending on what particular species I am growing this 25% org. might go down lower, and sometimes be 0%.
the org. used to be filled up by pro-mix, I think BX formula, which was composed of peat and also perlite so technically probably less than 25% organic material. Now I am using peat and pre mixing some perlite in now that I don't have the discount of the greenhouse for pro-mix, which is crazy expensive for a bale (never realized cause I had a discount lol)
The next component is about 50% aggregate. If I am not low I will use 75% and skip the third part. So the aggregate component over the years has varied with what I currently had free up. But this for a very long time was straight lava rock in general medium particle size sometimes small, which is hard to come by, I had some imported.
If I'm low on that which currently I am I will use my bonsai soil, which is 25% lava, of mixed particle sizes.
The next part is about an additional 25% perlite or pumice, whatever I currently have,sifted to a medium and large particle size. I also prewash all my perlite and pumice when I get it in to remove all the insane amount of broken down perlite and dust (hate that stuff) This is an important step if you don't wash all the dust and stuff out of the perlite or pumice then it will clog up pore spaces in the soil and won't drain as fast. Which negates the purpose of using it if you don't wash it.
So I do want to add with this mix you will have to water more, and fertilize more often. But for me this is a huge bonus, not a downside like it may sound.
I use this same mix for starting seeds and extremely rarely have any problems with damping off or other related fungal issues with seedling failure. Huge plus!!
I wish I had photos of my mix but I never take photos of it, I'm still fairly new here and new to sharing my "secret" mix, and I usually only make enough to use each time.
75% aggregate mixes are also highly reusable you just have to sift it back out every time you repot, and wash it again.. Some breaks down a little bit but not enough to throw away.
One other big advantage to a mostly aggregate mix is the amazing root development you get. I've experimented with this root development compared to other mixes and it's always better. Roots in this mix love the extra air filing up the pore spaces.
And no fungal or soil related diseases with this mix! At least not yet.
Then once repotted I top dress everything in aggregate. This seems to also stop the perlite from raising up in the soil as much.
Sorry for the very lengthy response but I want to share what I have had amazing results growing in. I have never found a downside to growing in mostly stone aggregate, actually quite the opposite, everything about it is a plus in my books. If any one has any questions please feels free to ask me and I will answer everything I can.
