I was going to ask the same question but you beat me to it.
How small are the seeds? Are they about the same size as begonia seeds? I noticed quite a bit of "dust" particles coming from the dried astilbe flowers... Are those the seeds?

Jeff

I need help too! I don't know how to harvest the seeds, though I do know the seeds are tiny. Would really appreciate advice.

Wow - I get to answer three of you at once! I wait until the astilbe flower heads are completely dry, towards the end of August/early September. I cut the entire stems below the flowers and place them upside down in a paper bag. I clip the bag to a shelf unit inside my garage and leave the bag open so they can finish drying. After a month or so I crush the dried flower stalks. The seeds are, as one of you said, as tiny as dust motes.

When it comes time to sow them, I just sow seeds, chaff & all. I winter sow the seeds and am growing some healthy-looking seedlings at the moment. The seeds don't need cold stratification according to my notes but Swallowtail Garden Seeds website says if they don't germinate after 4-5 weeks at 65-70 degrees, put them in the refrigerator for 4 weeks, then set them out in 65-70 degree temps again. Winter sowing is much less complicated than that--just sow the seeds/chaff in recycled containers, stick the containers out in the snow and ignore them until spring.

From my observations, astilbe (like many shade lovers) grows very s-l-o-w-l-y from seed and won't bloom until it reaches maturity so division is the best way to get mature plants that will bloom a year or two after being divided.

thanks a ton!

Thank you!! I have some to trade, as I don't need seedlings, but didn't know how to harvest. This helps a lot : )