I live in Ohio and I love these plants, too. I have them in my backyard and people stop and admire them all summer. I've even had my house identified as, "the one with those beautiful flowers in the yard." The only negative with these plants, and it's a huge negative, are the Japanese Beetles. They love them, too! It's a constant battle!
I have a hedge of 3 along one side of my driveway -same cultivar as in the pictures - I live south of denver in Centennial - zone 5 - I ditto everything in the article - Last to come up in the spring - someone always says your hibiscus look like they didn't make it through the winter - I don't fertilize - they get a little alfala from the lawn fertilization - last to bloom with the dahlias - no spraying - no bugs - watered with lawn - delicate looking but tough as nails and a showstopper. Mine were marked hardy at Paulino's - I didn't believe the tag - started them from one gallon pots 6 years ago - don't cover or mulch in winter. Mine are huge. LOVE THEM.
I;m a hobby gardener who has crossed the line into obsession. Must try everything. Out of room for new plants. Smile.
I live in zone 9 (Houston,TX) and my hardy hisbiscus is wonderful. However, I am told it blooms on new growth and so cut mine back each year. Of course, this plant rarely freezes here. We did have a hard, early freeze last new and it froze to the ground, but is back going strong.