Sushi, GREAT photo!
Most of mine planted themselves, cuz so many pods popped open before I had a chance to harvest the seeds.
Wherever they landed, they sprouted, often coming up between the gravel of other potted plants, but often right in the little bit of muck at the bottom of the pondsai.
I scooped the 'homeless' seedlings up (like the one in the photo) and weighed each one down onto the surface of a pot of soil with one piece of gravel, then they rooted themselves in.
These things are like dandelions...floating off to wherever they land and sprouting....very prolific.
The harvested seed I dropped onto the top of a pot of soil prepared with my traditional compost and Osmocote Recipe.
Then I put a very thin coating of pea gravel over the seeds,
exactly one gravel thickness deep.This holds the seeds in place while they sprout. They come up around the gravel.
You must VERY gently sink the pot into the water.
OH...and they will bloom the first year if you start them early.