Were the plants you've recently bought seriously pot-bound? If so, the plant will never be healthy - they've been starved in their infancy, and the roots will never work properly.

Sorry for the late reply! No, the plants weren't pot-bound. I always take them out of the pots, loosen up the rootball, and then plant in fresh soil. I haven't done anything different as far as I can tell, but they just aren't making it. I'm wondering if perhaps many of the nurseries in the area have been carrying a variety that doesn't do well in the heat of a FL summer? I'm trying again though - bought some more over the weekend.

I have had the same thing happen to all of my rosemary. It gets reddish and dry and dies. I just ripped out a bush that was a dacade old. I'm distraught. someone said spider mites. Does this seem possible.