Linda, Those look so nice, I'm sorry to hear that they aren't doing well. From your description, I thought that they were all a single unit. It should be possible to set them in some kind of waterproof container that could be filled with gravel (for decoration) that could be flooded during the really hot times. (next year, if these are too heavy now that they are filled) Of course, you might end up having to treat the gravel/water filled containers for algae down the road.
Lowes locally sells a selection of black , heavy-duty plastic, designed for water gardens and fountains, that could be used for such a purpose. I bought a couple several years ago to sit my EE collection in, so that I could always have their pots in water. They have come in very handy, as I also use them for mixing potting soil and other things.
By using water to cool the concrete, I was not implying watering the plants more. However, that is an option if they are drying out too fast. I was thinking more along the lines of setting the concrete in water or spraying down the outside during hot periods of time.
