Many people talk to their plants. Whether or not it makes a difference, we chatter on about the weather, how nice the plant is looking, perhaps how shiny a leaf or pretty a flower. Of course, the plants don’t really hold up their end of the conversation. I’ve heard nary a peep from my peony, nor a single ahem from my Agastache. Even if they could talk, I doubt we’d find the conversation stimulating. After all, plants don’t have brains. But a lack of brain and vocal cords doesn’t stop plants from communicating. We just have to learn their language.
Plants can actually “talk” to one another through various substances they emit from their leaves. For example, research has shown that if a particular bean plant is attacked by aphids, it manufactures chemicals to that deter aphids and attract parasitic wasps to help in its defense. These chemicals, called volatile organic compounds (VOCs) are released through the leaf pores (stomata) into the air.
Perhaps these beans are saying, “Warning! Attack is immanent! Prepare defenses!” When a nearby bean plant not under attack receives the VOC message, it too starts making those same chemicals! Dozens of studies on other plant species, from willows to sagebrush, confirm these results.
Rather than send a message through the air, some plants use their roots. Scientists in Israel studied pea plants subjected to drought. In the study group, the pea plants grew in sealed, isolated pots, but their roots were allowed to intermingle. Then one plant was subjected to drought. Here’s what happened, as reported by The Scientist:
Fifteen minutes after drought was initiated, the stressed plant closed its stomata—as did its nearest unstressed neighbor, suggesting some sort of drought warning sign had been passed between the two. After an hour, all five neighbors, each more distant from the stressed plant—the only one that actually experienced drought-like conditions—had also shuttered their stomata, indicating that they, too, received the message to prepare for drought. Importantly, in a control setup where root contact between neighboring plants was blocked, pores stayed open, indicating that the message was somehow being passed between roots.
When some plants want to send a message, they send a telegram. Mycorrhizae are tiny fungi that form a symbiotic relationship with plant roots. The fungi feed on sugars produced by the plant. In exchange, they help the plant roots absorb the essential nutrients phosphorus and nitrogen. And now it appears that they also pass along messages.
The scientists who studied VOC communication with beans and aphids repeated their experiments, but his time the plants were only connected indirectly through a mingling of their mycorrhizae. Sure enough, the uninfected plants that had a mycorrhizal connect received the warning; others did not.
Many species, including black walnut and knapweed (an extremely invasive weed in the sunflower family), produce biochemicals that scream “Keep out!” to other plants. These chemicals may be produced by the roots, leaves (leaching out of leaf litter as it decomposes) or other parts of the plant. The obvious advantage of these chemicals is to eliminate competition in the root zone. This is why it’s so hard to grow much of anything under a black walnut tree.
It makes sense that plants would communicate with biochemicals. Astonishing new evidence hints that they may also talk to one another in the same way we do—with sound!
First, a study published by Australian scientists in the journal BMC Ecology found that plants apparently respond to clicking noises made by other plants. A subsequent study by researchers at Bristol University discovered that corn seedlings emitted clicks as well. Then they suspended young corn roots in water and played a continuous noise at 220Hz—a frequency close to that of the plant clicks. The result was that the plants grew towards the source of the sound, much in the same way that plants bend toward the light. Sound has the obvious advantage of traveling quickly through the air or soil, and for longer distances than chemicals or fungi. (Is that why corn has “ears”?)
Plants are turning out to be far more complex than we ever imagined. Next time we talk to our plants, we might discover that they’re talking back!