That is how I lost my plumeria trees. I had sheets with Christmas net lights on them, they froze. We had two days of 27 degree weather, I had them outside for 13 years before the freeze. If I had put mulch around the base or pipe insulation around the branches, I think they would have made it, but I didn't. I just found out that the PSA members in Corpus, dig up their plants. They knock off the dirt,remove the leaves and store inside the garage off the floor. Some put them in the rafters, some store them in cardboard boxs. Once my plants get established this is what I plan to do. Barbra

I didn't use them this past winter, so I can't comment directly from experience, but I've heard of people using Xmas tree lights in conjunction with frost cloth or some other type of protective covering (that covers the plant without touching it). I guess you have to make sure you're using the old-school lights (not the newer LED ones), so that they actually generate heat!

My potted plumeria went into a temporary greenhouse this winter (Flowerhouse Planthouse 5), and they did fine. I even bought a small ceramic heater for it, but ended up not using it. Some of my plants in the greenhouse never went dormant!

My plumeria in the ground got covered with frost cloth (held up with stakes so that it wrapped the plant without touching it) - this also seemed to help. Of course, our lows were in the mid to upper 30s, not an actual freeze, so I just needed something to "take the edge off."