Thanks, Herbie, for the link to the "using two soils" thread. Good to know from all the seed-starting experts that Promix BX works fine, because that's what I generally purchase for my container gardening efforts like pots and EarthBoxes. One less type of soil to purchase is a good thing!
Regarding the little BioDome sponges, which I've used for three years with generally good success: I've come to the conclusion that they work best for me IF I use the right size sponge (they come in small, med., and large) for the seed. Too large a sponge for a small seed and there seems to be too much moisture held in the giant sponge, or maybe the little "hole" into which you drop the seed is too deep; anyway, no or poor germination. But big seeds like pumpkins, squash, sunflowers, etc., do fine in them. Little seeds work in the small size sponge--you basically drop one (or two if you wish to double-sow) into the hole. Really tiny seeds work better in seed trays where it's easier to broadcast them.
I found the BioDome system to be most useful when I was a complete newbie and needed a complicated "incubator-type system" to make me feel more confident. Now after a few years of experience and the help of this cubit, I may do more of the regular seed-starting trays.
