Good News: Plants talk, and now we're listening

Scientists at Tel Aviv University have conducted a six-year experiment, proving that plants emit an ultrasonic noise in certain stressful situations.  

Inaudible to human ears, the plants emit a high frequency clicking sound, and when starved of water, or damaged, the clicks become far more regular. The plants also made different sounds, depending on whether they were thirsty or injured. “Each plant and each type of stress is associated with a specific identifiable sound,” said Professor Lilach Hadany, who lead the research study. 

Plants were first placed in a sound-proof chamber then moved to a more natural setting in a greenhouse

Focusing particularly on tomatoes, grape vines, tobacco, wheat, corn, cactus, and henbit, the plants were placed in an acoustic box- a soundproof chamber- and recorded by two microphones on each.  

Some plants were starved of water, others cut, and a control group was left undamaged. 

The researchers used an AI algorithm to separate the noises, successfully differentiating between the sounds made depending on whether they were dry or cut. The algorithm was then trained to make these differentiations in a greenhouse setting. This included far more ambient sounds, but the algorithm was still able to decipher the particular distress calls of the plants, up to 3-5 metres away.  

Though it was not proven in this study, previous studies point to cavitation being the cause of the noise

Previous studies looking at the vibrations of a plant (rather than the sound waves in this instance) have shown that a plant exposed to drought will experience cavitation. This is a process in which bubbles form, expand and collapse in the stem. While the cause of the sounds wasn’t the focus in this study, it’s likely that cavitation is the answer.  

The sound is too high for humans to hear, but animals such as bats and mice are likely able to pick it up

On average, the human ear can hear sounds up to around 20kHz, whereas the sounds produced by plants are in the 40-80kHz region, far beyond our hearing capabilities. But that doesn’t mean they’re altogether undetectable. 

"While imperceptible to the human ear, the sounds emitted by plants can probably be heard by various animals, such as bats, mice, and insects,” Hadany tells us. Though this has yet to be proven, it’s possible that these creatures use this information for their benefit, choosing which plants to eat, for example. 

A study in 2014, led by Reda Hassanien of China Agricultural University in Beijing, also proved that plants reacted to sound waves, with some plants significantly increasing their yield, and their immune system. While it’s still unknown if one plant could react to another’s noises, it seems likely. So plants might very well be reacting to each other’s distress calls. Indeed, the same research facility is now testing both animals and plants to see if they respond to these newly discovered sounds. 

This new finding could save up to 50% of water expenditure for farmers

While farming has become a science itself, there’s still a lot of estimation involved. If farmers were able to receive accurate information directly from their crop, they could instigate a much more efficient method of care.  

The study claims that more precise irrigation could save up to 50% of water expenditure and significantly improve yield. “In times when more and more areas are exposed to drought due to climate change, efficient water use becomes even more critical, for both food security and ecology.” 

They would also be able to better identify and control disease in a crop. All this can be achieved by employing microphones and sensors to translate this new information. 

A field of flowers may seem peaceful, but in the right frequency it's very noisy

Rest assured, this is not the stuff of nightmares. While evidence shows that plants can react to sounds, there’s currently no evidence that they can actually hear them. The sounds emitted are not cries for help, but rather a by-product of material stress rather than deliberate communication. Regardless it’s fascinating to consider that there are signals all around us that we are only just discovering, as Hadany notes, “Apparently, an idyllic field of flowers can be a rather noisy place. It’s just that we can’t hear the sounds.” 

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