We looked at how Disney portrayed humans living on Mars in the 1957 Disneyland TV show "Mars and Beyond" but the depiction of possible plants on Mars may be even more imaginative.
According to Steven Watts in his book The Magic Kingdom: Walt Disney and the American Way of Life (p. 309):
"[Mars and Beyond] was the most speculative program [and] it veered near the realm of science fiction with its imaginative description of possible life forms on the planet, [and] Martian weather conditions..."
You can view a clip of the program here and you can find this program in its entirety on the DVD set Walt Disney Treasures - Tomorrowland: Disney in Space and Beyond.
Mars and Beyond (1957)