“Plants that need water or have recently had their stems cut produce up to roughly 35 sounds per hour, the authors found. But well-hydrated and uncut plants are much quieter, making only about one sound per hour. The reason you have probably never heard a thirsty plant make noise is that the sounds are ultrasonic — about 20–100 kilohertz. That means they are so high-pitched that very few humans could hear them.” Stressed Plants ‘Cry’—and Some Animals Can Probably Hear Them. When I was a kid, I was a picky-eating vegetarian who often wondered whether, if you listened closely enough, you could hear lettuce scream when you tore leaves from its head. Now I’m more worried.