might help to know where you are.. drought??.. heat waves?? watering schedule?? .. how deep that rock is?? and recent transplants..???

otherwise.. it looks like normal fall coloring.. to my eye.. after a hard summer.. they just look tired ... and buried in rock ...

BTW.. are they near a pool??? .. chemical damage???

ken

To answer your question: Stick your finger into the soil. Is it moist, wet, or dry?

If they were planted recently, check the soil of the original rootballs -- it must be moist until the roots grow into the surrounding soil.

The rocks look like they're on the crown of the plant, where they emerge from the ground. They need some air.