According to research, when the plant is dehydrated or pruned, it emits high-pitched, intermittent “screams” that a human cannot hear. If you reduce the frequency to a range that the human ear can distinguish, these stress-induced noises will sound like someone twisting a roll of bubble wrap.

What are the plants screaming about?

Previous research has shown that drought-experienced plants go through a process called cavitation, in which air bubbles form and collapse in the plant’s vascular tissue, causing a characteristic popping sound that can be detected by recording devices attached to the plant. While humans cannot hear these ultrasonic blasts without the aid of technology, various mammals, insects and even other plants can detect and respond to these sounds in the wild.

The team placed microphones near healthy plants as well as plants under stress. For this used tomatoes and tobacco placed in a soundproof box and a greenhouse. Stressed plants were either dried or stems cut off. The team also recorded pots containing only soil to make sure the soil itself did not make any noise.

• On average, healthy plants made less than one sound per hour.
• Stressed plants sounded between 11 and 35 depending on the plant type and stress factor.
• Drought-stressed tomato plants made the loudest noises, some making more than 40 sounds per hour.

The team loaded the recordings into a machine learning algorithm, an artificial intelligence system used to detect patterns in data.

• It turned out that the neural network trained with these data successfully discriminated the sounds of plants under stress in 70% of cases.
• The researchers also trained another AI system to distinguish between healthy and diseased tomatoes in a greenhouse with over 80% accuracy.
• Another model was able to identify which stage of dehydration the plant was in with around 80% accuracy.

In additional experiments, the team successfully recorded the sounds of diseased tomato plants infected with tobacco mosaic virus, and recorded the cries of various other stressed plants, such as wheat, corn, and cacti.

Although the researchers collected these recordings by placing microphones about 10 centimeters from plants, they suggest that these ultrasonic “screams” could potentially be heard by mammals and insects with excellent hearing from 3 to 5 meters away.