I must say I have become an "Air To The Roots" fanatic when I lost one of my babies grown from seed to rot. One day, it was doing fine. The following week, the leaves were gone and the caudex turned to mush. AAAARRRRGGGGHHHH!
The terracota pot in which it dwelled was sitting square on the concrete deck. A film of water formed between the pot and the concrete when it rained, or when I watered. From there, I guess anaerobic bacteria grew and eventually attacked my baby. Bummer!
I now raise my adenium pots off the concrete surface using 3 small pieces of broken ceramic tile around the bottom edge of each pot. That way, at least 1/4 inch (7 or 8 mm) of air flows between the pot and the deck. I haven't had another rot problem since then. Low-tech and easy: my kind of solution. As far as potting medium is concerned, I use the cheapest potting soil available at Home Depot, to which I add about 1/3 sand. It works for me.
This baby was rescued from a property where the abandonned house had been declared an "unsafe structure" and was scheduled to be demolished by the County the following day. The front lawn was such a mess that, had it not been for a pink flower sticking its head out of the tall grasses, I would have never known an adenium was growing there. While digging out the plant, we found the large (18 inches dia./45cm dia.) blue ceramic pot sitting in the back yard. It was being used as a garbage can and cat poo container. We came back with 2 rescued adeniums and the large pot. And it was my birthday. I must confess that I am not that fond of the blue glaze. One shouldn't look a gift horse in the mouth. Happy birthday to me.
Take care, all.
Sylvain.