ZuZu, since no one has given you an expert opinion, I'll offer my two cents worth. In Hawaii, where we lived for a time, we did have very cool nights in " winter." No one let their plumerias go dormant. If you have a solarium, I would think you could keep yours happy without them going dormant. I have a hoop house off the patio that I keep some of my larger plumerias in during winter. I have heat out there only when the temp is lower than 40. The plumerias bloom during the winter. I only take the ones that are in ground to the garage. I just have too many other tropicals to share the space that all the plumerias would take on the patio. I have observed that the ones that do not experience dormancy bloom sooner in spring. I also know that some that stay in the darkened garage pout, and don't bloom until much later in summer, if at all.
I would think California would have enough winter sun to keep plumerias happy in a solarium. That's just my opinion, though.
