I built a (temporary) GH inside my garage. It is 10'x6'x8'H and is covered with 16 mil solar blanket material. I moved all my (large) potted plumeria inside the GH as well as perhaps 75 cuttings, last week, before the temperature dropped to freezing. I trimmed all the leaves off, leaving only those tiny, terminal ones and left the seed pods as-is, according to Hetty's instructions. I first used a small, oil-filled electric heater, but it kept the temperature 80 F (on the lowest setting with the outside temperature getting down to 30 F), but have now switched to a "base-board" heater to lessen the heat generated. The solar blanket material really keeps the heat in and the cold out! My 18 seedlings are in a (real) GH and I will maintain them through the fall/winter months. The two that germinated last December are now 30" tall. The others range from 10" to 24".