I know my astilbes are only nice looking for so long. The flower heads do die off about mid-summer and just look brown. I swear they are brown so long I forget what color they really are. So I know this doesn't help you, but it may just be them acting normal.

Bob, you mean the leaves look brown and shabby? Could it be some kind of fungus or powdery mildew? If so, they may need better air circulation. They might do better in an area that gets a little more sun. When you water, just water the ground, not overhead.
I don't have astilbes, but I've seen this on some annuals I have. When I spaced them more and tried them in an area with more sun, they did much better.
I hope they improve for you.

Kat

Bob, I agree with Kat. I know folks think of astilbe as a shade plant, but mine are under an apple tree with only dappled shade and lots of air circulation, and they look good. Might try moving them this spring?

Con.

Well it could be a disease or fungus & I sure don't have a better idea. Maybe just a case of good plant wrong place. I'll have to try something else there. Too bad, astilbes seemed like a natural for that spot.........
Tx for the suggestions.

Well I'll throw in my two cent cuz I have the same problem. I think its a moisture issue. Do you have tree root competition? Are they inside the drip line of your roof? They need to have even moisture and even then may crap out on you in the heat of summer. You can try shearing them to the crown (not too close) when the leaves start to decline, they may or may not leaf out again before the end of the summer.

I have several varieties of astilbe in several different locations that have performed very well for a number of years. Last year, however, virtually all of them were in one stage of decline or another despite proper watering. My suspicion is that it was viral/fungal so I was extra careful in my fall cleanup. We'll see what this year brings.

tj

I made the mistake of planting mine next to the foundation... they don't stay wet enough! I'm moving them soon to a different spot. Rhubarb too. I don't know what's supposed to grown there, but I think I'll stick to grass....

:) Gina