Crassula Tom Tumb, also known as Crassula, is the ideal succulent for miniature gardens and terrariums. She is very aware of how colors work together, how to make the size of everything feel balanced and proprotioned, and finishes off with perfect accents. Moon Cactus is a South American desert plant, mostly Argentina. Its shape and size can vary depending on the species. The succulents were larger than the rest, with the medium-sized ones just beyond that. Finally, the majority of the succulents were about the same size as coarse sand.