I have two Endless Summer hydrangeas and they were doing great for about 2 months after I got them. In the last couple of months, it seems like every leaf is turning brown/black at the tip which then slowly moves through the rest of the leaf and it becomes dry. It's rare to find a leaf on them that isn't doing this. There is new growth from the root that looks okay, but any new growth from existing stems turns brown/black almost immediately. I tried pruning off some of the dead leaves, but then the remaining stems turned brown/black at the tip which then moved all the way down to the root.
I fertilized once when I planted them about 4 months ago with a slow-release fertilizer. A couple of months ago, I tried one application of a bloom boosting fertilizer. Once I saw how the leaves were turning and drying out, I haven't given them any more fertilizer since I wasn't sure if the fertilizer was the cause of the leaf issue.
I check these plants for water every day and they need water about every 2 or 3 days as they are on a covered patio so they get indirect sun/shade all day. Here in central Texas, it gets far too hot in the summer to keep them in the sun.
I've tried researching what could be going on, but I'm totally out of ideas at this point. They look like they're dying, but then there is new growth at the root which is confusing me even more. Any ideas you guys might have would be greatly appreciated!!
PS - The plants look a little dusty. That's just construction dust so not mildew or anything.