Plumaria plants what is the temperature when you should bring them indoors? My second question is can they survive in a plastic greenhouse?
Plumeria can be damaged by frost, so you should bring them indoors before the predicted first frost in your area. A plumeria could potentially survive in a plastic greenhouse, but it would depend on the temperatures in the greenhouse during the winter. The temperature should stay above 55 degrees for the plumeria to stay healthy, and should never drop below freezing in the greenhouse. Also make sure it doesn't get too overheated in the greenhouse (such as on sunny days in spring).