If Plants Could Think: The Science of Plant Intelligence

by Jeremy Johnson

The plant world is a complicated pharmacopeia. American philosophers and naturalists have long venerated the plant world for its ancient, primordial wisdom. “They do not preach learning and precepts, they preach, undeterred by particulars, the ancient law of life,” writes Herman Hesse. “I believe that there is a subtle magnetism in Nature,” Thoreau tells us, “if we unconsciously yield to it, [it] will direct us aright.” It’s not surprising that we still feel this way about nature. Especially in popular culture.

Why are there trees I never walk under

But large and melodious thoughts descend upon me?

—Walt Whitman, Leaves of Grass, 1892

James Cameron’s movie, Avatar, shows off a whole world that functions like one, vast, neural network. A living mind. Navi’s balanced ecosystem is achieved through plants and animals communicating with each other. Daron Aronofsky’s The Fountain explores the pharmacological promise of the Tree of Life—hidden deep in a Central American rainforest—able to cure disease and extend life indefinitely. More infamously, M. Night Shyamalan’s The Happening explored how plants could become the focus of a horror film where—spoiler alert—plants around the world learn to release a deadly, psychoactive gas, forcing hapless people in the vicinity to kill themselves. The last example is a little bizarre, but despite its mixed public reception, Shyamalan was adapting some actual science—albeit in a very exaggerated way. More on that in a second.

There’s a goofy scene in The Happening where Mark Wahlberg’s character tries to assuage a potted tree not to kill him. “Just want to talk in a very positive manner. Giving off good vibes,” he says, “we’re just here to leave the bathroom…I hope that’s OK.” Luckily, for Wahlberg, the tree is just plastic.

Still. The idea that you should talk with your house plants is a trivial familiarity. We’ve heard it before—somewhere—that playing classical music around plants helps them grow better. Especially Mozart.

But where did all these ideas come from? What’s the actual science behind “plant intelligence?”

Can Plants Think?

These ideas struck a cord with popular consciousness way back in the 1970s, when New Age ideas were just starting to get popular. A little book called The Secret Life of Plants, by Peter Tompkins and Christopher Bird, was published 1973.

There are many interesting vignettes in the book, from actual science experiments to more metaphysical musings. As one New Yorker writer describes it, The Secret Life of Plants is a “beguiling mashup of legitimate plant science, quack experiments, and mystical nature worship.” (Incidentally, this sounds like my kind of book.)

One story of note involves Cleve Backster, a C.I.A. polygraph expert who hooked up a houseplant—a dracaena—to a galvanometer. To his utter surprise, when he visualized the plant on fire, he could make the needle rise. He followed up with a series of experiments, where, he claims, plants would also react when other species were being harmed. Boiling live shrimp in the same room, for instance, would make the needle rise. Unfortunately for Backster, other scientists were not able to repeat his findings, and The Secret Life of Plants soon became the bane of credible research. Daniel Chamovitz, an Israeli biologist, credits the book for scaring away scientists from the field. Fortunately for our question—whether plants can think—the jury is still out.

Research became fringe after that, but it didn’t stop.

Green Bites Back

In 1983, new studies were published demonstrating that Willow, Poplars, and Sugar Maples were able to warn each other about insect attacks and even slow down the metabolism of their grubby assailants. The leaves chewed on by insects would release “volatile chemical compounds” in the air, triggering the other trees to release them too. These chemicals slowed down the growth of the caterpillars. When fed leaves from undamaged willows that lived nearby, caterpillar growth would also slow down.

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