Hi Ken, when using burnt earth, make sure you add some other elements like charcoal, coarse sand, perlite etc., this soil is water draning in the initial stage but it eventually turn harder and harder when the bigger pieces of soil break down to powdery form and stuck the airy holes in the soil.
I have used this for my rafflesiana plantlets, they died of root rot. After I mixed the soil with charcoal (small pieces), coarse sand etc. my other batch of rafflesiana look happy in it.
Just want to share my experience if anyone would like to use burnt earth as media.