Answer: Astilbe need to be divided every 3-4 years because they are heavy feeders and deplete the soil around them. They can be divided in early spring or fall. I think it is okay to divide them now. Make sure each has a good chunk of growing roots, but they are fast growers so you can break them down. They are shade lovers, but can take full sun in cool climates like yours if soil is moist. Put a layer of mulch down to help retain soil moisture.
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