According to Larry Hodgson's book Perennials for Every Purpose, " Astilbes like things cool and moist. They prefer light to partial shade."

I don't deadhead the flower stalks. In my experience it has no impact on the plants' performance from one year to the next but check the Missouri Botanical Garden to verify their bloom period.

My best advice: relax. Plants will do well or not based on your soil and how you plant them, not on what you do to or for them. They need space to spread their roots in healthy soil. Once established, stand back and let them do what comes naturally.

My garden is also Z6a. I grow perennials from seed via the winter sowing method. My garden beds are now full thanks to seed-grown perennials.

I've never heard or read that you need to deadhead astilbe. Just let them do their thing and enjoy them when they bloom each spring.

If they dry out enough so that the foliage gets brown and crispy it has been my experience that no amount of water will rejuvenate them. (Although they will come back just fine the next spring). But in a moist spring and early summer they can have some spectacular blooms.

When the real heat of summer hits, many of my varieties begin to brown up and turn crispy. That's when I cut them down to the ground. I never fertilize them.

Re chinese astilbe:
although I also have these shaded by taller perennials in summer, I do find they tolerate more sun than other astilbe.

and you can run into a lot of trouble.. having perennials and conifers on the same watering system ... they have very different needs ....

you can get IDs on anything.. in the appropriate forum .. including the name that plant forum.. by posting pix of things ...

its near impossible to answer your questions.. w/o really knowing what plants you have .. as i read your facts.. as saying there were more than astilbe

ken