With milder winters occurring in the last few years, there is a renewed interest in growing citrus in northern Florida and even up into Georgia. In the last few years I have worked with some farmers starting to grow satsumas in southwest Georgia. Once the trees are established, they can take temperatures down as low as 15 F without having significant damage, although temperatures colder than that can kill them. Here is a recent article about some work being done by the University of Florida on different varieties of citrus that are suitable for growing in this region.
