Researchers Discover Plants Emit Ultrasonic Cries When Experiencing Drought

If you forget to water your house plants, they might be complaining. Scientists have discovered that stressed plants emit high-frequency popping sounds when they are dehydrated or injured. These ultrasonic cries are completely undetectable to the human ear, but they reveal a complex communication system hidden in plain sight. Let us look at what these sounds mean and how researchers finally managed to hear them.

The Groundbreaking Discovery at Tel Aviv University

For years, biologists suspected plants responded to stress in ways we could not easily measure. A landmark study published in the journal Cell in March 2023 by researchers at Tel Aviv University confirmed this theory. Evolutionary biologist Lilach Hadany and her research team placed sensitive acoustic sensors near various crops to see if they produced airborne sounds.

The researchers did not start in an open field. To isolate the sounds, they began their work in a totally dark, soundproof acoustic box. They placed microphones about four inches away from the stems of tomato and tobacco plants. Once they confirmed the plants were indeed making noise, they moved the experiment to a busy, commercial greenhouse. The new environment was filled with the sounds of wind, air conditioners, and human activity. Despite the ambient noise, their technology successfully pinpointed the ultrasonic distress signals.

What Do the Cries Sound Like?

When a plant experiences severe dehydration, it starts popping. These sounds are not like human cries or animal vocalizations. Instead, they closely resemble the sound of bubble wrap popping or kernels turning into popcorn.

The frequency of these acoustic emissions ranges from 20 to 100 kilohertz. Because human hearing caps out at a maximum of around 20 kilohertz, these high-pitched noises are totally silent to us. The scientists had to use specialized software to lower the frequency of the recordings so human ears could process them.

The Mechanics of Plant Noise

Plants do not have vocal cords, lungs, or moving parts. So how are they generating these acoustic signals? The process comes down to simple fluid dynamics.

Plants transport water from their roots up to their leaves through a system of tiny, microscopic tubes called the xylem. As a plant dries out, the physical tension inside these water columns increases dramatically. Eventually, the water column breaks under the pressure, forming a tiny air bubble. This bubble expands and then rapidly collapses. This physical reaction is known as cavitation. When the bubble collapses, it generates a tiny shockwave that creates the popping sound picked up by the microphones.

Quantifying the Stress of Thirsty Plants

The Tel Aviv University team discovered that the frequency of the popping correlates directly with the level of stress the plant is experiencing.

Healthy, well-hydrated tomato and tobacco plants are mostly quiet. They emit less than one popping sound per hour. However, when the soil dries out, the complaints begin to multiply. A drought-stressed tomato plant emits an average of 35 popping sounds per hour. Tobacco plants emit slightly fewer, but still produce dozens of pops an hour under severe dehydration. The scientists recorded the sound frequency peaking on the second or third day without water, right before the plants started to visibly wilt.

Machine Learning Listens In

To make sense of the massive amount of audio data, the researchers turned to artificial intelligence. They trained a machine learning algorithm to analyze the greenhouse audio recordings.

The computer models successfully learned to differentiate between the sound of a healthy plant, a thirsty plant, and a plant with a cut stem. The AI achieved a 70 percent accuracy rate in identifying the exact condition of the plant based on audio alone. It could even identify the specific species of plant making the noise just by analyzing the acoustic signature. This proves that the sounds contain highly specific, actionable information.

Beyond Tomatoes and Tobacco

While the primary focus of the 2023 Cell study rested on tomato and tobacco crops, the researchers quickly expanded their testing. They placed acoustic sensors near several other species to see if this popping phenomenon was universal.

The team successfully recorded ultrasonic stress sounds from wheat, corn, Cabernet Sauvignon grapevines, henbit plants, and even cacti. This widespread success suggests that acoustic emission is a fundamental biological function across the entire plant kingdom, rather than an isolated quirk of just a few species.

How Animals Use Plant Sounds

The fact that these sounds travel up to 15 feet through the air opens up fascinating questions about natural ecosystems. Scientists believe other organisms in the environment actively listen to these acoustic cues.

For example, a female moth looking for a place to lay her eggs might hear the popping of a dehydrated tomato plant. Knowing the plant is stressed and might soon die, the moth will likely choose a healthier, quieter plant nearby to ensure her caterpillars have enough food. Similarly, mice and bats rely heavily on ultrasonic frequencies for navigation and foraging. They could easily detect these emissions and use the information to locate moisture or find insects gathering near weakened plants.

What This Means for the Future of Farming

This discovery has massive implications for modern agriculture. Farmers currently rely on visual cues or soil moisture sensors to determine when to water their crops. Unfortunately, by the time a plant looks visibly wilted, the crop yield has already suffered irreversible damage.

By installing acoustic sensors in greenhouses and open fields, farmers could listen to their crops in real time. If a specific section of a tomato field starts popping at a rate of 30 times an hour, the irrigation system could automatically turn on before any permanent damage occurs. This type of precision agriculture would save billions of gallons of water annually while significantly boosting global food production.

Frequently Asked Questions

Can humans hear plants screaming? No. The sounds plants make range from 20 to 100 kilohertz. Human hearing stops at around 20 kilohertz, making these popping sounds completely inaudible without special equipment.

Do plants feel pain when they make these sounds? There is no scientific evidence that plants feel pain. Plants lack a central nervous system and a brain. The popping sounds are the result of a physical process called cavitation, much like a wooden floor creaking when the temperature changes.

Do plants make sounds when they are cut? Yes. The researchers at Tel Aviv University found that plants emit a similar rapid-fire popping sound within minutes of having their stems cut.

What kind of microphone is used to hear plants? Scientists use specialized ultrasonic acoustic sensors. These are highly sensitive microphones designed specifically to capture frequencies well beyond the range of standard audio recording equipment.