I bought a young Duncan tree several years ago near Houston and happily planted it. Less than a year later an unusually cold blast overcame the significant cold protection that I had set up to protect the small tree. It died. Apart from the lemon-flavored Bloomsweet variety, grapefruit just don’t have the ability to survive icy events. It’s like the old papaya description: Cold hardy to 33 degrees. Laughable. One local citrus enthusiast said that the Duncan was the best tasting GF that he has ever eaten.