Article from Azcentral.com - 12/27/2007 - Cold-sensitive plants such as petunia, begonia, lobelia, impatiens, coleus, Ficus nitida, poinsettia, bougainvillea, hibiscus, plumeria and lantana, water night before expected frost. Valerie Meyers, a National Weather Service meteorologist, said to expect near or freezing conditions in the desert at least through Friday morning, thanks to clear skies, light winds and extremely dry air.

http://www.azcentral.com/news/articles/1227frost1227.html