Listening to Plants Talking

Roald Dahl’s books and stories have been a persistent influence in our family’s fiction. I’m pretty sure that my kids read all of his children’s novels, exhausting our local library’s collection and then pulling in the rest of the books from the county’s inter-library loans. They’ve even enjoyed some of his short stories written for older audiences, with Lamb to the Slaughter being particularly noteworthy for the way it opened up their imaginations to the role of irony in storytelling.

Lately I’ve been thinking about another short story he wrote for the New Yorker back in 1949, called The Sound Machine. I wouldn’t rank it among his best works, but it does have all the characteristics of a Dahl story. A boring suburban tinkerer builds a machine that can listen to sounds outside the normal range of human hearing, and in the course of his testing, he discovers that rose bushes shriek whenever his neighbor snips off a flower, and that a tree grunts as an axe chops into its side. The consequences of these discoveries are deranging for the machine’s inventor, and the story ends with him staggering back to his home, supported by his doctor.

What Plants are Really Saying

Last month some researchers in Tel Aviv published results showing that tomato and tobacco plants create specific popping sounds when they are stressed. The sounds are far above our hearing range, but using audio processing software they could accurately identify which plants were drought stressed and which plants were being snipped by scissors simply by listening to them. The work is so new that its implications haven’t been teased out. It is thought that some moths have the ability to hear in this frequency band, so there is some speculation that these sounds might be a tell that a plant is sick, similar to the way a wildebeest’s limp catches the eyes of hunting lions, signaling that the moth will have an easier time attacking the plant.

But this leads to the question: why would a moth need to know that a plant is doing poorly? Can’t a moth just eat any plant it chooses? Observant farmers and gardeners have long noticed that pests prey on sick plants more readily than healthy plants, and that insect infestations are often signs of underlying drought- or nutrient-related imbalances. And this leads to a larger body of research into plant responses to predation. A team in Wisconsin demonstrated that tomato leaves actively change chemical composition throughout the rest of the plant within seconds of a caterpillar bite. So a healthy plant can quickly respond to insects, creating unpleasant flavors or even toxins to ward off attacks. And other research is demonstrating that plants are capable of differentiating between types of attack, so they respond differently to leaves being cut versus being crushed. We often think of plants as passive in all respects beyond growing and reproducing, almost as if they are entirely constrained by their environment. But we’re constantly learning that there is much more going on, that they are controlling and even creating their environment.

We now know that plants can release chemicals to “call in airstrikes” from the predators of other insects that are eating them (source and another source). And one sagebrush plant can signal to others in the area to prepare for attack. And then there are weirder special cases, like venus fly traps demonstrating counting mechanisms and mimosas exhibiting a sort of memory response. Tempting as it is to anthropomorphize this as thinking, none of this is operating at the same level of neural cognition as we experience in our bodies. But we can’t dismiss it either; something special is happening here. We have to acknowledge that plants are gathering signals from their environments and taking the kinds of actions that are consistent with the word “cognition.” Even if we can’t point to a brain, information processing clearly emerges from the complex system. They are interacting with information and processing it to create dynamic and adaptive responses. As uncomfortable as it might make us feel, there is some kind of cognition happening in plants.

Listening to the Plants, or Telling Them to Listen to Us?

As I watch our cattle grazing the bright green spring grass, I wonder at what might be happening down among the leaves. We have a farm where a diverse community of plants grows up and then is subject to short bursts of grazing. What chemical signals are the plants releasing in response to the cattle? We know that many of these plants have developed alongside grazing animals, and research has demonstrated that plants respond differently to grazing versus mowing, so grazing isn’t just the same as clipping, only using animals instead of blades. Maybe some plants are becoming less palatable with each bite, signaling the cattle to back off before they graze too far. It might be that other plants with seeds could be telling the cattle to keep on eating, so that the seeds will later be spread through the manure. And flipping the view, what might the cattle be signaling to the plants through their saliva or the chemicals in their breath? There are so many questions here, and probably a lot of questions I haven’t even thought of yet.

Contrast our farm’s diverse perennial pastures with the way so much of industrial agriculture works, where a monocrop is planted on chemically suppressed soil. These crops grow in blocks of hundreds of acres, an uninterrupted sameness row on row. The plants sprout in an environment that has all the elements of earth, but everything is manipulated in a most unnatural way, so the fungal populations, bacterial populations, insect populations, and native plant populations are all wrong. The history of plant breeding selected for seeds that perform in an environment that is as unnatural as possible, where the innate survival traits have been selected against in favor of maximizing yield as measured in bushels per acre, where all the fertility comes from a spray tank and all the pest control is pumped out of another spray tank. These are lobotomized plants growing in lobotomized soil. Is it any wonder that nutrient levels in our foods are dropping?

Instead of changing agriculture to more closely mimic natural systems, biological entrepreneurs have been busily applying this research to create products that can reproduce plant defenses. It seems that our system of incentives only privileges solutions that generate more sales, so soon we’ll have more sprays that simulate the chemicals that plants release to protect themselves from pests. And we’ll have other sprays that encourage predators to eat those pests. And because we raise our crops in fields that provide no habitat for those predator species, we’ll grow all those bugs in monocultures in labs and introduce them into the fields as we spray. With every step we chase the illusion of control further toward a receding horizon, even as each action spins off new unintended consequences and uncontrolled outcomes. But rest assured, for whatever we break, there will be a sales rep with a new product guaranteed to fix that problem. Maybe the next solution will be nanobot drones with tiny ultrasonic speakers putting out just the right frequency to scare bugs away from our corn and wheat and beans.

“Help! Stop picking me! Ahhh!”

When I was little, I remember bringing vegetables in from the garden with my dad, and he told me that the plants were probably hollering at us as we picked them. And then he indulged me with some gruesome sounds of vegetable agony. I was at just the right age where I didn’t quite believe him, but the idea stuck with me because it didn’t seem entirely impossible either. I thought, maybe my ears were still too small and when I had my grownup ears I’d be able to hear it all for myself. It’s hard not to imagine that as we pull and twist a carrot out of the soil that the resistance we feel is coming from a determined, conscious opponent, actively resisting us in the struggle for survival.

Maybe Dad and Roald Dahl were both onto something, even if they were only tuned in to the dramatic bits that made for the best storytelling. It is becoming clear that plants do more than holler when they’re hurting. It’s not all screams of pain. Rather, plants are communicating constantly, by internal chemicals within the leaves, by sugars signaling into the root zone, by gaseous clouds of compounds broadcast to their neighbors, and now it seems that they might even be using these newly discovered high-pitched sounds to communicate. A healthy landscape is not a quiet place – it is loud with the chatter of all its living things, from the internodal networks of mycelial fungus, to the leaves of the plants, to the insects signaling each other, and even to the larger animals providing their feedback. The more I learn, the more I appreciate the opportunity I have to participate in this complexity, even if my grownup ears still can’t quite hear most of what his happening all around me.

6 thoughts on “Listening to Plants Talking”

    1. There are some interesting implications if we push back the boundaries of sentience to include plants. I really don’t know what value to assign to plant cognition, or even if we should, but it might suggest that the act of eating vegetables isn’t without its own moral ambiguities, so that even a plant-based diet cannot hold itself blameless by its internal standards.

      I’m not ready to lean heavily onto that line of argumentation because I’ve never been convinced that judging whether or not something is sentient should be held to be germane to the ethics of eating that thing, but that’s a different topic, and one that veers off into realms that always seem apt to focus on the art of the philosopher more than the work of the farmer or the choice of the eater.

  1. Wonderful writing and subject matter. Eons ago I read about plants responding to different types of music. I don’t know if those were well designed studies, but modern science has shown that plants communicate through their roots, fungi help plant roots access minerals, etc. We are stupid and ignorant to think we can design ecosystems better than Nature does.

    1. The music thing seems to still be debatable, so I didn’t include it here. It may be true though. And yes, the interactions down in the roots from plant to plant and from plant to fungus is a fascinating topic.

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