Hi everyone. Will astilbe bloom the first year if I start them from seeds? I understand the seeds are tiny. Does anyone know if they are as tiny as petunia seeds? Those tiny dust-like things called seeds are a bit challenging. Thanks to anyone who has an answer for me.

No, it usually takes about 3 years for them to bloom from seed.

A trip to the nursery will be in order for plants instead of starting seeds.
This year I'm putting in a semi-shade garden and of course, want immediate results. Can they be divided the after the first season? Or should they be in the ground a couple of years first. Divide spring or fall? Thanks for your answer.

They can be divided in either spring or fall. I would let them get 3 years old before dividing, that way they will be large enough to get a few good divisions.