Where I grew up in the Pac. Northwest the hydrangeas really liked to be in shade for most of the day, and summers there are most likely cooler than where you are. The one that gets 6 or 7 hours of sun might do better with more shade. Also morning sun is more gentle than afternoon sun, as the temperature is generally cooler in the mornings. So if you have a location with either of those two conditions available, a move might help. Or plant a small tree to shade them in the afternoon?
They also like lots of moisture, and soil high in organic material so adding top dressing of compost as Cindy suggests would be good, and you should do it every spring as well as fall. Also I would definitely fertilize them with a timed release pelleted fert in the spring as soon as you see the leaves starting to open out. Big, established hydrangeas might do ok without a lot of fert, but small ones just trying to get going need all the help they can get.
