I have two in small, maybe 4" glass containers, one is in bloom and I may try to self it. My mix is sphagnum mixed with fine perlite.

Thanks so much for the info! I will repot them today. Do you fertilize, and if so, what do you use?

I don't have the variegated type but for all the other small terrarium plants I use the same mix for the rest of my begonias (Miracle Gro). Seems to work fairly well. I do have to add a very small pinch of fertilizer every few months though to green things up.