Answer: Astilbes are generally pest and disease free, so problems are more often related to watering issues. Usually, lack of water causes the foliage to brown beginning at the tips and edges first and starting at the top of the plant first. Browning at the base first could indicate overwatering, although that is somewhat unlikely because this is a plant that likes evenly moist soil. It does not however do well in soil that is constantly saturated/sopping wet. It might indicate they were planted too deeply or have settled excessively and so the crown is too low, or they are too deeply/heavily mulched with the same result. The leaves can also turn brown in response to excess heat, especially if the soil is on the dry side. Since these are new plants and are not yet fully rooted, you might just be seeing some stress. Yet another possibility is a disease problem such as mildew or leaf spot -- to some extent these are related to weather conditions and will also be more likely to affect a stressed plant. Since dead foliage will not regrow, I would suggest removing it. Take care not to damage new growth when you do that. In case it is disease related, dispose of the dead foliage in the trash. FOr the same reason, do a thorough clean up this fall. Make sure the soil is evenly moist like a wrung out sponge, avoid wetting the foliage when you water, and use an organic mulch about two inches thick over the root area but not touching the stems. This will help keep the soil more evenly moist. Hopefully fresh new growth will come in quickly. If the problem recurs, you may want to consult with your local county extension for a more specific diagnosis.
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