An excellent grower in our society pots Tolumnias like this: She forces four corks vertically into a rectangular pot just big enough to hold them in one layer, with substantial compression - there should be no movement at all. She sets the bare-root Tolumnia into the central gap. No other medium. I don't have a photo. I'm doing this next time I get a Tolumnia (soon.)
__________________ May the bridges I've burned light my way.