Question
I have a hibiscus which gets about 60%+ of each day's bright Michigan sun but it has begun to grow lengthy, straggly but remains prolific.    Is not enough sun my problem?    I have another in a more sunny spot and it does exceedingly well.

Answer
Sun is probably at the root (sorry, couldn't help it!) of your problem.  But don't discount other potential contributors.

Is this plant pot-bound?  Check the roots.

Does the plant need to be pinched -- the top pruned, perhaps 3 inches, to open up lower parts to light and air?

Check the undersides of the leaves for insects.  Look closely.  VERY closely.  See anything moving?  Possibly spidermites are a problem here?

rsvp with the answers and we'll figure this out, Don.  Thanks for writing!