Sounds Plants Make

US Person's high school biology project was an investigation of the effect of sound on the growth of plants.  He concluded based on his data that growth of bean plants was stimulated by sound.  Since that time there have been more, professional studies of the positive response of growing things to sound.  Now, wine growers in Italy broadcast classical music in their fields to encourage the grapes to mature.A recent study has taken this field of investigation to a new level.  Researchers at Tel Aviv University have concluded that plants emit airborne sound.

recording tomato plants

Although not audible by humans, plants under stress emit ultrasonic vibrations. that contain information about their status.  It has been known for some time that plants experiencing extreme drought produce cavitation in their xylem causing vibrations that can be detected by a recording device attached to the plant.  But the question of airborne sound transmission has remained unanswered until now. Researchers studied tomato, tobacco, wheat, corn and grape in an acoustic box and in a greenhouse.  After filtering out noice using AI the stressed plants emitted airborne sound in the neighborhood of 50-60kHz, too high for humans to hear (20 kHz).  But the result explains why his cat became agitated when he cut his hydrangea plant down to a manageable size.  Cats can hear up to 64kHz.  Dogs also can hear in this frequency range. Here is a recording of a stressed tomato plant, slowed down into human audio range. 

Further, researchers showed that the sounds edited by their study plants differed according to the condition of the plant, for example with the extent of dehydration.  Thus, plants produce sound that contains information about their status that presumably can be interpreted by other nearby plants. Insects, such as moths, can hear frequencies in the hundreds of kHz. (300kHz for the wax moth!) The implication being that if a moth wants to lay eggs on a healthy plant, it can determine a plant's condition by listening to the sounds it emits.  If you are a farmer you may be able in the future to conserve your water use and improve yield by selective irrigation determined by plant sounds.   That encouraging possibility requires further study. [photo credit: Tel Aviv University]