Answer: Astilbe prefers full sun to part shade and thrives in rich, moist, cool soils. The clumps should be divided every 4-5 years (but I'll tell you from personal experience that you may need to use an axe to get through the rootmass!).
If yours isn't flowering, it's obviously unhappy. You might want to dig and divide, replanting in well-amended soil, in a slightly sunnier spot. Be sure to water regularly during the growing season.
Hope your astilbe rebounds and provides lots of bright plumes this year!
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