For centuries, the plant kingdom was regarded as the realm of silence. Plants do not move, do not speak, do not scream. Or at least, that’s what science claimed— until a team of Israeli biologists placed an ultrasonic microphone next to a tomato and discovered that we had been mistaken all along.
50 clicks per hour, as loud as a normal conversation
Researchers from Tel Aviv University, led by evolutionary biologist Lilach Hadany, placed tomato and tobacco plants in a completely soundproof chamber, then recorded what happened using ultrasonic microphones capturing frequencies between 20 and 250 kHz — well above the human hearing threshold (20 kHz max).
The result, published in the prestigious journal Cell in 2023, astonished the scientific community: stressed plants emit series of snaps — “pops” comparable to popping bubble wrap — at about 65 decibels. It is as loud as a normal conversation. A thirsty tomato plant produces on average 35 clicks per hour. A plant whose stem is cut emits even more.
And the most puzzling part: healthy plants, by contrast, are almost silent.
Each species has its own “voice”
The team did not stop there. The researchers trained an artificial intelligence to listen to these sounds and classify them. The algorithm learned to distinguish a thirsty plant from a wounded plant with 70% accuracy. It could even tell apart the “voices” of tomato and tobacco, even amid the background noise of a greenhouse where people were talking and work was happening nearby.
And tomatoes aren’t the only “speaking” plants. The team later tested wheat, corn, grapevines, and even cacti: all of them emit sounds when stressed. The plant world around us is literally full of sounds — we were simply deaf to their frequencies.
A Language That Others Are Already Hearing
If these sounds are inaudible to the human ear, they lie squarely within the frequency range perceptible to many insects and mammals. A bat, a moth, or a mouse can detect these signals from several meters away.
The implications are dizzying: it is possible that insects are already using these sounds to decide where to lay their eggs. That a moth might avoid a stressed plant — or, conversely, target it because it is weakened. That nearby plants, too, “hear” and react. The Tel Aviv team had previously shown that certain flowers raise their sugar concentration in nectar in response to sound vibrations.
As for the mechanism behind these sounds, the researchers suspect a phenomenon called cavitation: when a plant is water-stressed, air bubbles form and burst within its vessels — a little like creaking joints. So this would not be an intentional form of communication, but a physical signal that evolution may have turned into a source of information for an entire ecosystem.
The Beginning of a Revolution
As Lilach Hadany summarizes: the world around us is filled with sounds emitted by plants, and these sounds carry information — about their hydration levels, about their health state, about their species. Information we never knew how to exploit — but which nature itself may have been capturing for millions of years.
The next time you forget to water your plants, know that they are not suffering in silence. You simply were not equipped to hear them.
Source: Khait et al., “Sounds Emitted by Plants Under Stress Are Airborne and Informative,” Cell, 2023. Link: https://www.cell.com/cell/fulltext/S0092-8674(23)00262-3
