Zen Garden's Calming Effect Due to Subliminal Image? [The Zen rock garden of the Ryoanji Temple in Kyoto, Japan] after all, has no plants—no flowers, no trees, not even any weeds. Visual-imaging scientists in Japan say they've figured out what it is about the garden that engenders this serenity. The secret: The more than 500-year-old garden is harboring a subliminal message in the form of a tree.

So the calming effect of a completely plantless garden is due to its resemblance to a tree.