I've read they can be cut to the ground in zone 6. I cut mine back to 1 foot each fall. Hope this helps.
Loretta5

I have a couple growing as standards and yes, I prune them back to about 3 - 4 feet in late winter or early spring. By the end of summer they are about 6 - 4 feet tall.

Pruning anything in the fall is a bad idea IMHO.

Alexa

I've got Rose of Sharons popping up all over the place, and prune some of them pretty severely.

I recently cut a huge one down to about two feet. It seems to be thriving, although not blooming this year (I must have cut off the buds). Next year it'll probably be covered with flowers.

And I've seen them sheared as hedges. They're tough.

The question might be pretty much answered by this point, but I will chime in that last fall one of my dogs decided to prune a Rose of Sharon (one of those new hybrids with double flowers and a Greek name that I don't recall).

He chewed and/or broke all stems at about a foot and I had to clean it up from there. I was concerned that it might look funny and/or not bloom this year (if it was one of those blooms-on-old-wood situations).

But it looks great -- maybe even better/more compact than before -- and is blooming nicely (although maybe a little later than it otherwise might have).

In the future I won't hesitate to give it a haircut as needed!