What Made My Rose of Sharon Die?
I have had 15 Rose of Sharon trees along my fenced lot line for over 10 years. They have always been healthy and bloomed every year. I have kept them trimmed to form a hedge for privacy. Last summer they were beautiful. I trimmed them back early this spring but they never leafed out. They all died. Every one of my trees died. When I cut them back in the spring, they had live branches. Now it's July and I'm cutting them down to the ground. They are easily breaking off and the limbs are spongy and almost powdery. I have a fear that someone in the neighborhood poisoned them but don't know what would kill all of them. I took a branch to a local nursery and they said they wouldn't rule out poisoning and it didn't look like they had a fungus. What could have happened? I will say that while taking all the dead trees down, I'm finding new growth coming up around the base and weeds have grown quite well in the entire area where they are.
A view held by many nursery professionals is that one cannot kill a plant by pruning at the wrong time of the year. Doing so might result in reduced harvest or bloom, but not in plant death.
You say there is new growth showing. Get rid of the weeds and take care of your 'new' altheas.
Speaking from experience, I trimmed an entire crop of 3 gallon buddleia, in early spring, before new growth started. Every one of them died. Lesson learned, wait until new growth starts showing before trimming. (If that's not fact, it's my belief, and I'm just superstitious enough to stick to it!)