Answer: I've found that late in the season the foliage on my astilbes look brown and burned, too. Usually it just indicates the plants are ready to go into dormancy, but in your case in might indicate a need for more water. One or two hours of morning sun is necessary for best plume color, but hot afternoon sun can really take it's toll on the foliage. A contributing factor is soil that's too dry. You might try mulching over the soil beneath the plants with several inches of organic mulch to help conserve moisture and to keep the roots from overheating in the summer months. Hope this helps!
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