The popular notion of a tomato plant “screaming” when cut is fantasy, but the scientific reality is surprisingly close to the myth. Plants lack vocal cords or the biological capacity for audible cries of distress. However, modern acoustic research reveals they are far from silent, especially when under duress. Tomato plants emit distinct, measurable acoustic signals that are too high-pitched for human ears to detect.
The Scientific Reality of Plant Sounds
Tomato plants release high-frequency acoustic emissions in the ultrasonic range, often between 20 and 100 kHz, when stressed. These emissions are outside the human hearing range, which typically extends up to 20 kilohertz (kHz). The sounds are not continuous noise but a sequence of rapid, distinct “clicks” or “pops.”
The mechanism behind these sounds is cavitation, a physical process occurring within the plant’s vascular system. Water travels through microscopic xylem vessels, held together by high negative pressure. When tension becomes too great, such as during water scarcity, the water column breaks. This causes tiny air bubbles to form and rapidly collapse, releasing a shockwave of energy measured as an ultrasonic acoustic emission.
How Scientists Detect Ultrasonic Plant Emissions
Detecting these high-frequency acoustic events requires specialized equipment, as the sounds are outside the range of human perception. Researchers use highly sensitive, contactless ultrasonic microphones positioned near the plant stem to capture airborne emissions. These recording devices often operate within an acoustic chamber to minimize environmental background noise.
In a real-world setting like a greenhouse, scientists focus on the 20 to 150 kHz range, where typical background noises like wind and insects are less dominant. The captured ultrasonic data is processed and analyzed using sophisticated computer algorithms, including machine learning models. These models are trained to differentiate the plant’s characteristic “pop” signals from other environmental sounds. This processing provides a clean count and pattern analysis, making the specific patterns of stress-induced sounds measurable and classifiable.
The Triggers: Why Tomatoes Make Noise
The acoustic emissions are a direct byproduct of the plant’s physiological response to stress, primarily severe drought and physical injury. A healthy, well-watered tomato plant is almost completely silent, emitting very few clicks per hour. When subjected to water deprivation, the rate of acoustic emissions increases dramatically, sometimes reaching 30 to 50 clicks in an hour.
The plant begins to emit these sounds before any visible signs of wilting or dehydration are apparent. The pattern of the clicks conveys information about the nature of the stressor. Machine learning models can accurately distinguish between the acoustic signature of water stress and that of a recently cut stem. The sounds are loudest during the peak of the water-stress period before decreasing as the plant completely dries out.
This acoustic signaling holds ecological significance, possibly serving as a form of communication within the environment. Research suggests that organisms like insects, which can hear in the ultrasonic range, may detect these high-pitched signals. Certain moths use these distress signals to avoid stressed tomato plants, preferring to lay their eggs on healthier, quieter specimens.