Chemical Communication

Probably the best-known way that plants communicate with one another is by giving off and detecting chemicals known as volatile organic compounds (VOCs). Whatever chemicals they’re giving off will send a message to the other plants around them.

What kind of message would a plant want to send?

Well, for a start, “Back off!” If another plant gets too close, plants release chemicals into the soil that can actually stunt or slow the growth of other types of plants. Then there’s “Watch out!” Plants can warn other plants through chemical signals in the air or soil about problems like an insect attack or drought.

Good Vibrations

Another form of plant communication uses ultrasonic vibrations to signal other plants about threats like damage or disease. These are sound waves that are too small for our ears to pick up, but plants can apparently pick them up — scientists believe they may use parts of their flowers to “hear.” And with super-sensitive microphones, scientists can tune in, too.

Even without ears, plants can actually “hear” quite a lot! For example, they can hear a chewing caterpillar and start sending out warnings to emit bad-tasting chemicals. They can even hear when pollinating insects come close. Then they’ll start sweetening up their nectar to offer them a treat.

The Fungus among Us

We’ve always known that trees shared water and minerals underground through their roots. But not long ago, botanists (plant scientists) started noticing that trees were connected beneath the soil by tiny fungus networks. (You may know of mushrooms, which are fungi, but the fungi we’re talking about are much, much smaller, like tiny threads).

These fungi seem to carry “messages” from one tree root to another. They especially carry distress signals — about insects, drought, or disease — which help other trees prepare to deal with the crisis. Some scientists believe that the fungi also help carry carbon, an essential mineral, from one tree to another. This could help young trees survive in shady areas where they aren’t getting a lot of nutrition any other way. What’s in it for the fungi? In return for helping the trees, the fungi get a tiny bit of the sugar that the trees produce out of sunlight, and a safe, cozy forest home.

Electrical Communication

Scientists are beginning to explore another way that plants communicate — through electrical signals. It’s the exact same electricity as in the walls of your house, but in a very, very tiny dose. Plants give off electrical signals when they’re injured. For example, dandelions give off electrical signals when their leaves are touched or damaged. If a dandelion is touching another dandelion — in nature, they hang out together and fill whole fields — then all the dandelions can quickly pass around the signal. Different plants do different things when they receive danger signals. Some close up their flowers or “wilt” to make themselves look less attractive; others release chemicals to make themselves taste bad.

How Plants Find Out about Their World

Besides using communication to send messages to one another, plants and trees are also constantly receiving messages from the world around them.

The Bright Side

Even though they can’t see, many plants use light to receive important messages about the world. Sunflowers are one common example; they can sense and respond to changes in sunlight, even following the sun with their heads, which helps them grow stronger and produce more seeds.

Late in the summer, many trees sense that they’re getting less daylight, and they start preparing for winter. They trigger their leaves to stop making chlorophyll, the chemical that makes them look green. They also stop sending water to their leaves, because they need to save the water for the winter. With the chlorophyll gone, the leaves’ green slowly fades, making them turn color — red, brown, orange, or gold, and with no more water, they shrivel up and fall off.

Tender to the Touch

Plants also respond to tactile communication, which means they’re sensitive to touch. Climbing plants, from sweet pea flowers to beans in your garden, will feel around with their growing tip to find support (like a string or pole) to climb up as they grow. Some plants, like Arabidopsis, a relative of cabbage and mustard, will stop growing and can even get sick and die if they’re touched, though scientists aren’t sure why. And Venus Fly Traps and other carnivorous plants use their sense of touch to know when an insect has wandered in so they can snap shut and get to work digesting it.

Talking to Other Species

Plants not only communicate with each other, they also communicate with animals and people, especially when they’re trying to convince us to pick them, eat them, or plant them.

Sweet Chemistry

Fruit trees use chemical communication to turn their fruit sweet and juicy, which lures us in for a snack. Some plants communicate with wasps by giving off “distress call” VOCs when they’re attacked by insects. The wasps help the plant by quickly destroying the insects.

Navigating by Sight

Plants also “talk” visually. Some plants turn flowers a bright white color that’s easily spotted by night insects. And while humans can’t see infrared (heat) radiation, insects can. By being slightly warmer than pine trees, pine cones invite bugs to come and feast. Then, when the bugs leave, they carry along the trees’ seeds to distant locations.

Travel Plants

One of the most fascinating ways that plants communicate may be by making us enjoy them. Tea, coffee, and chocolate all contain chemicals that are slightly addictive to our brains, which could help explain why they’ve spread so far all over the world. Other plants like wheat, apples, and grapes can be turned into alcoholic drinks (beer, cider, and wine). That made these plants popular travel companions in ancient times, traveling wherever boats or caravans could reach.

Coordinated Communities

One final fascinating fact: Just like us, plants don’t like to live all by themselves, but they also don’t want to live anywhere that’s too crowded. You might think they couldn’t do much about it, but in fact, as scientists are just beginning to understand, plants are active participants in a complex dance called “quorum sensing.” When there are too many plants in a particular area, plants send off chemicals that invite insects to come in and take over. In this way, they naturally cut down the plant population until the neighborhood feels just right.

Communication Appreciation

Communication is hugely important for the survival and reproduction of all kinds of plants, and it’s an exciting field that scientists are starting to learn more about. Some of the facts coming to light are truly astonishing. Did you know that some plants recognize their “family” and won’t compete as much with “siblings” (plants from the same parent) as with strangers for space underground in a pot?

One final thought. It’s important to remember that when we say plants “communicate,” it’s not the same as human communication. Plants can’t think; they don’t have brains or nervous systems the way animals and people do. But Hashem has given them these simple methods of sending and receiving messages to help them survive and to create a better world for all of us to share.

So next time you’re out for a walk, stop and smell the roses… or tickle the tomatoes… run your toes through the grass… or just lean up against a tree and say hi — and thanks.

(Originally featured in Mishpacha Jr., Issue 947)