See what came in my mail today....
It was a seeded postcard from Ribbit!
The instructions were to plant the entire postcard in the garden or in a pot, so I filled a container with potting mix and moistened it using hot water. Hot water moistens a dry mix immediately, so you don't have to soak it for hours on end.
I placed the postcard on top of the damp potting mix. I was tempted to soak the card in water first, but I'd have felt terrible if all the seeds had fallen off of it, so I just followed the directions.
I covered the postcard with a 1/4" layer of potting mix that I had combined with an equal part of vermiculite. That should make it easy for the little seeds to push their way through.