lower leaves turning gray, shriveling

[gabbo23]

Hello!

We recently planted a hydrangea that gets a good amount of both sun and shade. We've been watering it frequently due to a stretch of hot weather, adding Miracle Gro to the water about once a week.

But the lower leaves are turning gray and shriveling up. We've noticed the same thing is happening with the lilac and rose bushes we just planted.

Does this sound like a soil deficiency, or something else? Has anyone encountered this before?

Thank you!