Answer: There are a number of possible causes for this but a very likely one this year is the drought. These shrubs are shallow rooted and need an evenly moist yet well drained soil in order to stay alive. If you have not kept them watered this summer that is probably the explanation. The rule of thumb is an inch of water a week from the sky or the hose and for these shrubs, several inches of organic mulch such as shredded bark should be spread over the entire root zone to help keep the soil moist and cool.
If on the other hand you have been watering, it is possible you have watered too much. These plants like a moist soil but not a soaking wet soggy one. Dig down and see how effective your watering is (or isn't) so you can judge better how much to apply at a time.
There are also a number of disease and insect problems that can make the shrub look like it is drying out when in fact the roots have adequate moisture. You might wish to take a sample to your County Extension (915-1399) for a more specific diagnosis and suggested cures.
Good luck with your shrubs!
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