I own a couple of Hoya plants but I'm not sure how active a specific Hoya Forum would be. I don't remember for sure but I think someone asked about having a Hoya Forum in the beginning days of ATP but maybe it was decided that the Houseplant Forum was the best place to discuss and share photos since most folks grow them as houseplants? I went to the houseplant forum and did a search for Hoya and got a return of 58 matches found so I'm assuming Hoya's were discussed on all of these threads even though some subject lines were about other plants:
http://garden.org/forums/searc...
edited to add: oops ... I couldn't edit to add a thumbs up icon. I'm sure if there were a specific Hoya forum, I'd more than likely participate in discussions and sharing photos.
