A plant that commercial nurseries should know about. I have the white one, that cannot make seed, called 'Diana', having eliminated several really beautiful ones that made real pests of themselves. Just plain tired of pulling seedlings, by the dozens, near and far from the parent, like 'Blue Satin'. Sterile Rose of Sharon are the thing of the future, with as much appeal as the newly introduced sterile forms of Buddlea. Your local agricultural college or Botanical Garden might be interested, and I believe even some well advertised major plant marketers should also know.

There are a number of sterile cultivars of RoS on the market and most have been around for at least 20 years. The description of yours matches that of 'Helene' rather closely.

Sterile RoS cultivars are the result of controlled breeding programs rather than the selection and cultivation of a chance seedling. It is far more likely your plant is one of these sterile selections than the spontaneous appearance of a unique, sterile seedling. So chances are very good commercial nurseries, et al, are already very familiar with this plant :-)