Pelargonium endlicherianum is one of two oddball outliers in the genus that are found in Turkey or nearby, far from the center of the genus distribution in South Africa. It is quite cold hardy, as evidenced by these exceptionally splendid specimens which I photographed in August in the display rock garden at LaPorte Avenue Nursery in Ft. Collins, Colorado. There were many other treasures in that fine nursery too, but this was the grandest display I have ever seen of Pelargonium endlicherianum, though I did see it doing well in a few other gardens in Colorado.
This species is more difficult to grow in the eastern states, not because it can't handle the winter cold, but rather because it rots easily during hot humid weather. Success would be best in a well drained elevated spot, which is how it seems to be planted even in Colorado gardens. I will try it in the future in the space near the wall at school, parts of that favored area get quite dry during summer, which is more like what happens to it in its native habitat. Otherwise it can be grown as an alpine house plant, with careful attention to watering during summer. Its bigger brother, P. quercetorum, from the Iraq/Turkish border (Kurdistan) is even more scarce in cultivation, but I hear it does well in New Mexico, and it does grow in Denver too.