There are actually (at least) two - In "The Big Dish (1969)" and "The Gypsy (1970)" palm trees can clearly be seen along the skyline in the outdoor scenes. This is not to mention that Hogans Heroes is usually portrayed as being set in Germany during winter, and yet all the trees in the background are sporting healthy, green summer foliage. But, palm trees in Germany - that's a little too much to believe.