last year i too suffered loss of a big titanum..sigh..heartbreaking.. sigh
i did some surfing looking for ideas.. now i use a potting mix that i am having
great success ..
not sure would work in all growing conditions/environments..
i use 70% pine bark chips..and 30 % pumice..similar size to the pine bark..
i have alot of water flow thru the potting mix..of course.. but from last growing
season (2013) the unpotted amorphs..konjac,paeoniifolius,amorph species.. the unpotted
corms looked great..fantastic root systems..some corms had root systems pushing potting
mix out of the pots..
none of my largest titanums are dormant yet.. my 2 smaller titanum, 1 hewettii that are dormant..
had great roots and are now just starting back in growth again..
as has been mentioned..potting mix isnt the only consideration for successful growth..
i use a biological fungicide with every watering.. this seems to help fend off fungal growths
on the corms..
i know its only mid winter here.. but im sure anxious to get plants outside..back in full growth. and especially
see how largest titanums,and 1 medium sized hewettii did in corm growth !!!!