I've never really understood the concept of "they need dark/light to germinate." For seeds planted under the soil, it's dark anyway. And, in the wild they don't get to block out the sun to sprout.

At least now you don't have to find a way to give them dark!

Sara,
Thought a lot about that also.
Always felt that seeds that need dark, germinate under the fully leafed out mother plant before the mother plant dies. I concluded that was it. But then I read that there are other seeds that drop in dark places like swamps, etc. They need dark.
Maybe others naturally grow under tree or plant leaves that have fallen.
But as you say, "For seeds planted under the soil, it's dark anyway. " Certainly think that makes sense.
Don't think that dark means dark, rather shade. But then I am still experimenting. May change my mind tomorrow. :-)

I've never had success either way. In the shade they will sprout, but then grow sooo fast that by the time you uncover to check them in the morning they are 2 inch long threads that never recover....I find vinca hard to grow.