What did I do wrong?

All my other flowers did fine, but this never even took off. Will it still come back next year?

The new growth looks pretty healthy. It's definitely not dead yet, anyway. Maybe it just had a rough time adjusting over the summer if it didn't get enough water, or too much sun. As far as I know, astilbe pretty much needs full shade. I wouldn't give up on it. I planted some astilbe last September when we were just getting over the hottest driest summer I can remember. By October they looked dead. But they came up beautifully this spring. If the brown leaves are due to a disease, then that's another story. I've never planted any in the spring, so I don't know how they typically react to transplanting during that time.

I agree with erdooley. Looks like lack of water and/or too much sun. Astilbes like moist soil and at least partial shade. If it doesn't totally dry out, it should come back next year.

Well that seems to be the problem...Too much sun. Is it to late in the season to dig it up and move it?

As long as it is hanging on, I would wait until fall. The heat of summer is not a good time to transplant. When you do, make sure you give it plenty of water. Good luck. :-)

Not too late at all; In your zone Sept. should be a perfect time for transplanting. Move it to somewhere more shady, cut off all the dead leaves and even cut back the green stems by about 1/3 (this is so the plant's energy goes more towards root growth), ensure it gets enough water (they do like consistently moist soil) and it should be fine.
I love astilbes too. Good luck!

Thank you everyone for your replies and advice.

When you do transplant it, a little shot of Miracle Grow Quick Start in that water wouldn't hurt. It would encourage it to put down good strong roots.

Remember the old saying about most perennials: the first year they sleep, the second year they creep, the third year they leap. Follow the advice above for moving, and don't expect a huge plant just yet.

From my experience, Astilbe are heavy feeders. I give them some organic fertilizer the beginning of every month (or about the same time every month). I like to use Espoma Flower Tone or Plant Tone. I also just bought the Dynamite Organic for next year which feeds for 2 months at a time (I think that's what the label said). They can handle it drier if they're in mostly shade but I agree they prefer moist soil to be at their best. They're really pretty when in bloom so don't give up on it.

Until the weather cools down a bit try to build a little sun shade for your plant, you could do this by sticking 3-4 garden canes into to soil around the plant and attach a piece of sacking/cloth and this will help to give a bit of shade in the area you find the sun most powerful, I would wait till about October time to move this plant in your zone, the soil will still be warm enough not to chill the roots but the air will be cool enough to prevent so much transplant shock before it goes to sleep in the winter, you need to add as much organic matter to the planting hole to help retain some moisture and give the top soil a mulch to help stop the soil drying out also, dont put the mulch over the stems or you could cause rot, but normally these plants given the right conditions are as tough as old boots, these plants take a couple of years to really fill out as they are trying to make a good root system and also make flowers, I would cut off any flowers for this year so it dont make any seed heads as this will definitely weaken the plants root system when it is still so young and tender. everyone is right about the shade and moisture in the soil, they love this and you find them growing so well beside the edges of ponds etc where they receive the good moisture they love, you did good to grow this from seeds in the conditions you have it in, so just correct this now and enjoy next year, well done and good luck. WeeNel.

It's hard to tell from a photo, but your soil looks a little lean. Astilbe need rich soil with a lot of organic matter worked in. They also prefer to be evenly moist and out of direct sun. I wish I had better luck with them, but I don't. I work in a garden where the asilbes requirments are being met and they look like the ones in the garden catalogs. They also like a fairly thick layer of mulch to keep them moist. I agree with all above who said it will take a year or two for the plant to start to look lush and healthy. Is there any chance this plant caught the over spray from an herbicide? If not, follow the advice of the others above and you will have a fuller, more beautiful plant this time next year.
Chris

Before I went to school for horticulture i played with these in my new yard. I didn't know or care about the sun. Well, they did great until the hot summer hit then they looked like yours. Surprisingly, the next spring they came back, really nice and when summer hit it started all over again. So, I finally moved them to a shady area and they did great. Sometimes we have to go through the trails before we get an understanding, but plants can be pretty tough.