While I was off footballing in Utah, we got down to around 40 F two mornings. All my tropical plants are still outside, including over 100 plumeria. When I returned home I found that only the Scott Pratt plants dropped leaves, and oddly enough, the leaf-drop was from the upper 1/3 of the plants, not the older, lower leaves. It appears that the Scott Pratt is far more cold sensitive than the other 15-20 varieties I have. Live and learn.