Hi cherryblossoms, I start moving them if our overnight temps starts going below 55F. Even though we still reach 70's daytime, it is the overnight temp that is dangerous. Especially if they are newly rooted ones still very young, move them indoors. I move mine into one of our empty south facing rooms. So it becomes like my greenhouse of sorts. Then I reduce watering my Plumerias to make them go into dormant mode. The irony of our location, we get the rains in winter..but it is cold rain, the tropical loving succulents will not like it and may kill them altogether.
I would also move the Crown of Thorns indoors. They are Euphorbias, and they like to be kept warm. When I first got them, I thought they can handle the cold, big mistake, some died, some made it. So best to bring them indoors again by a south facing window.
What is the temperature in your garage during winter? It might be too cold for your plumeria. Best to keep them indoors. I notice my outdoor temps is just the same in the garage..freezing cold too during winter.
