The new cold hardy citrus that are becoming available this year is the Orange Frost and Arctic Frost. As I understand, these are not grafted but are a cross of the Changsha and Satsuma varieties. The Orange Frost is hardy down to around 18-20 degrees and the Arctic Frost is good to 15-18 degrees. I have had an Orange Frost for two years. We were able to acquire them from the test productions at our State Master Gardener Conference in San Antonio in early 2012. I allowed 9 of the oranges to mature this year and they were very good. None of them had seeds. The size of the fruit ranged between the size of a golf ball and a tennis ball.
I covered it during our extreme cold and so far there doesn't seem to be any damage.
