This is a question which everyone has, but is the hardest question to answer. With citrus trees, this can be even more difficult to answer than for other plants. Although citrus, like all plants, have definite limits to how much cold they can take, where that line is drawn depends upon not only the lowest temperature reached but also the duration of the freeze, the size and health of the tree, how well watered the plant is preceding the freeze, micro-climates, and what mechanical protection is used in the landscape. (Taken from the booklet "Hardy Citrus For The Southeast)- Millet