The sounds of stressed plants beyond our hearing

HostWe usually think of plants as the ultimate silent neighbors. They just sit there in the sun, maybe lean toward the window, but they don't exactly speak up. But it turns out, if you have the right kind of ears, a thirsty tomato plant might actually be one of the noisiest things in the room. How did we even figure out that plants aren't as quiet as they look?

GuestIt started with some researchers who basically put plants in soundproof boxes with very sensitive microphones. They looked at things like tomato plants and tobacco plants. When these plants are happy and watered, they stay quiet. They might make one sound an hour, maybe less. But when you stop watering them or if you start cutting their stems, they start making these clicking or popping sounds. It's not just a little bit of noise, either. A stressed plant might pop thirty or forty times every hour. To us, the room feels totally still, but in the world of high frequency sound, that plant is basically shouting.

HostBut we don't hear anything when we walk past a wilting flower. Is the sound just too soft for us to pick up?

GuestIt's too high. Our ears can only pick up sounds within a certain range. These pops are what people call ultrasonic. Think of it like a dog whistle. It's a real, physical sound moving through the air, but it's vibrating so fast that our eardrums just can't catch it. If you took those recordings and slowed them down so our ears could actually process them, it would sound a bit like bubble wrap popping or someone tapping hard on a desk with a fingernail. It's a very sharp, short burst of sound.

HostWhy would a plant pop? They don't have vocal cords or lungs. It sounds more like something is breaking inside them.

GuestThat's a great way to put it because that's basically what's happening. It's all about how they drink. Plants have these tiny tubes that act like straws, pulling water up from the roots all the way to the leaves. When a plant has plenty of water, that flow is smooth. But when the soil gets dry, the plant has to pull harder and harder to get any moisture out. That creates a lot of strain inside those tubes. Eventually, tiny air bubbles form and then they pop or burst inside the plumbing. It's like when you're at the bottom of a milkshake and you keep sucking on the straw, and you get those sharp cracks and pops. It's the same kind of physical stress, just happening on a tiny scale inside the plant.

HostOkay, but then it's just a side effect of them drying out. It's not like they're trying to tell us they're thirsty. It's just a mechanical sound, like a floorboard creaking when you step on it.

GuestFor a long time, that was the standard view. We thought it was just the sound of the plumbing failing. But when researchers looked closer, they found that these sounds are actually pretty distinct. A plant that has been cut makes a different sound than a plant that's just thirsty. And because these sounds travel through the air, other things can hear them. If a moth is looking for a place to lay its eggs, it might hear a stressed plant popping and decide to go somewhere else because that plant is clearly struggling and might not be a good food source for its babies.

HostI'm not sure if I buy that. A moth has a tiny brain. It feels like we're turning plants into characters in a movie if we say they're talking to bugs.

GuestI get why that feels like a stretch. We definitely shouldn't think of it as a plant having a conversation or a moth having a deep thought. It's more about how nature uses every bit of data available. If you're a bug and your survival depends on finding a healthy plant, you're going to use every sense you have. Evolution is very good at picking up on those cues. If a plant is literally clicking in the air, that's a signal, whether the plant means it to be or not. There are even signs that other plants might react. Some studies suggest that if one plant hears its neighbor popping from thirst, it might start closing the tiny pores on its leaves to save water before the drought hits it too.

HostSo it's like a silent alarm system that has been running under our noses this whole time.

GuestIt really is. And now that we know it's there, we can use it. There's a lot of talk now about using this in farming. Imagine a greenhouse where the watering system is hooked up to these high speed microphones. Instead of watering everything on a set schedule, the sensors could listen for those first few pops. The sprinklers would only turn on when the plants start clicking for a drink. It would save a massive amount of water because you're letting the plants tell you exactly when they hit their limit.

HostThat sounds like a smart way to farm, but does every plant do this? What about a tree or the grass in my yard?

GuestThat's one of the big questions right now. We know it happens in plants with those specific types of water tubes, like tomatoes, wheat, and corn. But we don't hear much from things like moss or lichen. They handle water differently, so they might be truly silent. But even with trees, it gets complicated. A tall oak tree has a lot of internal pressure, so it probably makes all kinds of noises we're just starting to map out. We only really proved this was happening in the air a few years ago, so we're still in the early days of learning who the loudest members of the forest are.

GuestThe most surprising thing is that even when we're not around, the air in a field of crops is likely buzzing with these sounds that define which plants survive and which ones get eaten.

HostThe next time I look at my wilting peace lily in the corner of the room, I'll have to remember that the quiet is just a trick of my own limited hearing.