I have always experimented with soil mixes - I think I have used about every one that has been devised during my growing lifetime - and I have found all those that were of coarse and gritty texture, thus providing excellent drainage and root aeration, consistently produced healthy and robust plants. In consequence I have always used very porous, well aerated, soil mixes for cultivating potted cacti.
In addition to producing healthy looking plants, ease of plant maintenance is an important attribute of soil mixes in my opinion. They should tolerate occasional watering misadventures and be light enough to make potted plants easily transportable. The over-riding soil attribute for me (because of my disabilities) is light weight!
I now use a soil mix that consists of 70% coarse pumice and 30% bagged coco-peat (coconut coir).
This mix is very lightweight and provides superior drainage and optimum soil aeration. I have found it to be ideally suited for cultivating all arid land plants in our extremely dry and hot southern Arizona environment
Soil mix dampened in preparation for posting
Root ball of Discocactus growing in soil mix
Close-up pic of root ball
