Melissa,
It sounds like your astilbe are experiencing transplant shock--not surprising considering how hot it's been there. All of the plants you mentioned like to be quite moist. You'll need to keep an eye on them and water them more frequently than other plants, particularly these first few months. I have clay soil here in upstate NY and have had a lot of problems with them when first transplanted, which I believe are due to water issues. I would just be diligent about the watering and look for signs for new growth over the next few weeks as proof that your plants are finally happy. This kind of transplant shock takes a while to work out of their system. Good luck! Astilbe & brunnera are GREAT! (do you have the Jack Frost brunnera--a stunner!)
Another Melissa

Hi melissa!
You and I are going through the exact same thing now. I planted a very large shade garden and finished putting in the identical plants just a week before yours went in. My Astilbe were doing the same as yours. It is now 3 or so weeks later and I have a ton of new growth on them below the older foliage. I did a number on them as I had divided them 2 or more times per each gallon pot. I have been watering daily because we have had so little rain. All are doing well now and seem to be thriving.

I've had astilbes die back after transplanting. They seem to always pop up again in the spring.

I transplanted my astible last year and I thought it was dead. Coming up great now!

I use a root stimulator to help with transplant shock. I also fertilize with fish emulsion, and my new astilbes are looking good. Maybe this is the key to it all?

This may sound kind of weird, but I also think that using rainwater helps the blow of being transplanted as well. I am noticing that the newer plants I have look better after rainwater is used on them. Mother nature knows best!

I noticed that when I moved one of my older astilbes to a new place last year, it took awhile to get going. It is still smaller than it was where I used to have it. Maybe astilbes are just very sensitive?

My 2 new astilbes are looking worse and worse. Wilted to the point that the stems almost appear to be breaking. Leaves dragging the ground. I watered again last night (we've had a good amount of rain, but it's clay soil that I amended, and I'm still new at this) and made sure I didn't have mulch crowding the stems (they were fine). Someone said that I should not have put down preen after I mulched (or at all), though that was 3 weeks ago now, and I'm not sure what, if anything I can do about it now (it was the pellet kind, and I don't see any lying about). I believe i used root stimulator. The other new plantings nearby are also having mixed results. The hostas and heuchera/heucherella are doing great, japanese forest grass appears to be doing fine, but an elderberry bush appears to be browning and dying on the interior foliage (it is also a bit floppy but other than the browning/dying isn't nearly as pathetic as my astilbes). Are these just dead/dying? Ideas/thoughts/suggestions?

Ditto for my astilbes 'Deutschland.' Nine were planted May 10th and seemed to be doing fine until around the first of June. Three appear to be pretty far gone - curled and brown leaf edges, droopiness, etc. I think they have received plenty of moisture and have well drained amended soil.

I'm in area 8b and I wonder if this is a stretch for them given daytime temps over 90. Could it be just the consistent heat that is doing them in?

As a follow up...mine are recovering and looking happy! I even see the beginnings of blooms. Wow, I am excited. :-) In my case, the problem was...water. Duh. Mine are in clay, morning sun/afternoon shade. I amended the holes when planted and mulched. Last weekend I put down some compost and reupped a bit on the mulch. I've now been watering 2x/day. Both those and the golden elderberry are now looking great! These are the first plants I've ever done beyond annuals (no, really, I'm serious), along with a bunch of hostas I've put in this year, and I'm awfully excited to see they aren't dying on me.

I found one looking terrible. All the ones around it are fine. I put some extra water on it and "fed" it besides, but a week later no change. I guess it is not getting worse..but I think today I will dig it up and divide it. It is not a good time for this but I don't know what else to do.