Rhododendron austrinum can make a giant shrub, if grown in the right conditions. It has taken over a large portion of my rock garden. How big does it get? So big that I could barely fit it into the frame of my picture.
Obviously, this species will make a multi-stemmed shrub. Though the max height is usually ten feet, this one is twelve, and still growing. I have one more normal sized plant. Swallowtail butterflies love both.
This is definitely not the hardiest of the natives, but it still grows like crazy here on the southern end of zone 7. I will also add, they grow equally well without any fertilizer. Neither of my two plants have ever had any.
Southern Fusion Cooking 