The requirement for damp or moist soil is permanent, its not just when they're flowering - those are the conditions Astilbe likes, so keep the plants watered if October is dry, but you can stop by November.

Thanks Bamboo regards, Nellie.

Astilbe; False Goats Beard or Meadow Sweet. Astilbe grows wild and thrives in the moist soil beside woodland streams.

meadow sweet is a different plant Jimmy, its Filipendula vulgaris. According to my wild flower guides we don't have a native Astilbe.