Plants aren’t silent. They make clicking sounds, a study finds

Plants make popping sounds that are undetectable to the human ear, according to recordings made in a new study

(CNN) — Plants make popping sounds that are undetectable to the human ear, according to recordings made in a new study — and they make more sounds when thirsty or under other kinds of stress.

The research shakes up what most botanists thought they knew about the plant kingdom, which had been considered largely silent, and suggests the world around us is a cacophony of plant sounds, said study coauthor Lilach Hadany.

She said she had long been skeptical that plants were completely noiseless.

“There’s so many organisms that respond to sound, I thought there was no good reason for plants to be deaf and mute,” said Hadany, a professor at the School of Plant Sciences and Food Security and program head of the George S. Wise Faculty of Life Sciences at Tel Aviv University.

The first plant Hadany recorded, using an ultrasonic microphone, was a cactus in her lab six years ago, but she couldn’t rule out that the sound she detected was made by something else in the environment. Previous studies had shown that plants made vibrations, but it wasn’t known whether these vibrations became airborne sound waves.

To figure out whether plants actually were emitting sounds, Hadany and her team commissioned soundproofed acoustic boxes.

The researchers placed tobacco and tomato plants in the boxes, rigged with ultrasonic microphones that record at frequencies between 20 and 250 kiloherz. (The maximum frequency that a human adult’s ear can detect is about 16 kilohertz.) Some of the plants had cut stems or had not been watered for five days, and others were untouched.

The team found that the plants emitted sounds at a frequency of 40 to 80 kilohertz, and when condensed and translated into a frequency humans can hear, the noises were a bit similar to the pop of popcorn being made or bubble wrap bursting.

A stressed plant emitted around 30 to 50 of these popping or clicking sounds per hour at seemingly random intervals, but unstressed plants emitted far fewer sounds — around one per hour.

“When tomatoes are not stressed at all, they are very quiet,” Hadany said.