Sharon, the Astilbe is setting seed now, but I think they are not ripe yet. Last year I hade the same problem, couldn't find the seeds. If I can find the seeds this year, I'll let you know, but it might take some time.
Hi Jonna. Thanks for trying to come to my rescue again! I did find a bit of a thread on gardenweb where someone said they just planted all of the dried stuff that they got, and had success. Could be that the seeds are so tiny that it might not be worth trying to find and seperate them.
I have Goatsbeard seed-heads that I pulled off (it's in the same family,right), and couldn't find the seeds, so I "rolled" one of the pods in my finders and several tiny black specks came out. Same thing out of several different pods. I'm thinking these are the seeds. I'm going to try germinating those AND try the whole pod, to see what works. Hope that helps.
And to think I was hoping to learn about some seed-sorting tool that I was unaware of - a seed finder! Gee, wish someone would invent it. Thanks for the info ptilda. I just tried that with the dried flower heads - I don't think I'd call them pods and found a few flat tear-shaped bits and a few the same shape except for points on both ends. It's not clear that these are the seeds, but they could be. What do your seeds look like?