Plants make a lot of noise when injured or thirsty, new study finds

Plants can be just as noisy as humans when they’re under stress, but they don’t make the sounds at a frequency people can pick up, according to a new study.

Researchers at the Tel Aviv University put plants in an acoustic box and either cut their stems or didn’t water them for days to see if the vegetation would emit a sound in adverse conditions. 

Ultrasonic microphones were positioned about 10 centimeters away to record whatever noise was made by the tomato and tobacco plants, as well as wheat, corn, cactus and henbit.

“Our recordings indicated that the plants in our experiment emitted sounds at frequencies of 40-80 kilohertz,” Lilach Hadany, the study’s lead author and a professor from the School of Plant Sciences and Food Security at the Wise Faculty of Life Sciences, said in a press release. “Unstressed plants emitted less than one sound per hour, on average, while the stressed plants — both dehydrated and injured — emitted dozens of sounds every hour.” 

The study described the sounds themselves as click-like, or similar to the popping of popcorn. The sounds are also emitted at the same volume that people talk to each other, but humans can’t pick up on noises that are higher than 16 kilohertz.

However, researchers theorized that animals such as bats, mice and insects can hear the plants and use that information for their benefit.

“We believe that humans can also utilize this information, given the right tools — such as sensors that tell growers when plants need watering,” Ms. Hadany said. “Apparently, an idyllic field of flowers can be a rather noisy place. It’s just that we can’t hear the sounds.”