You'd do better to split the astilbe rather than trying t grow from cuttings. There is lots of advice on how to do so on the web and now is a good time.

Just dig up your clump, give it a hair cut and divide it. Easy peezey :)

A good way t split perennials is to use two garden forks if you have them. Put them into the middle of the clump back to back and lever the handles apart. this rips the clump in half with minimal damage to roots.

Or do as I have just done, wait until the vine weevil grubs eat most of the roots away, pull the remainder of the plant out of the soil, wash the base of the plant, split it up into dozens of babies and pot them all up to see what happens.

Good one Owdb.!

Lol...

4 weeks on and the roots are out of the bottom of the pots. Now what do I do with 12 pots of Astilbe pumila Sprite?

Plant them :)

You are victim of your own success Owdboggy!
Send them to a bazaar or Freecycle them?