Ah, ha! That last picture with the marble rocks in it gives us a clue. Marble rock should never be used for mulching or under plants that like an acidic soil. They leach alkaline substances and raise the pH of your soil, sometimes to the point that the plants can't utilize the nutrients in the soil even if there is plenty there.
Some people put lime under hydrangeas to turn the flowers more pink, but from many I've seen (not here, but where I come from in BC they are very common) it can also make the plants suffer this way.
I'd remove all the marble rock from anywhere near the plants and water them with a weak, soluble fertilizer, about half strength of what it says on the package.
Still, it's not uncommon to lose some lower leaves on new plants anyway. As long as the new (top) leaves are healthy, and it stops before fall, I wouldn't worry too much.
