I asked Alan Elliott for his help because he has worked with the folk of the begonia collections in RBGE and Glasgow and he said .... " Seeds need humidity and light so surface sow, don't cover the seed with compost. The need to be misted regularly or put them in a sealed ziplock bag or in propagator if you have one to keep the humidity up.
They also seem to germinate better with their mates so plenty seed in a pot Its the happy medium thing of too many and it become impossible to tease them apart or not enough and they don't germinate very well.
Sterile seed mix is needed too as they might get swamped by other stuff if they are slow to germinate.
And as with all plants, good seed and luck.... "
I forgot to ask about the substrate
![Undecided :-\](http://www.srgc.org.uk/forum/Smileys/default/undecided.gif)
so waiting to hear about that!