Plant Communication – Can Plants Talk to Other Plants?

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Robert Pavlis

By now you have seen lots of headlines that say plant communication exists, including The Wonderful World of Plant Communication, How Plants Secretly Talk to Each Other and Do Plants Have Something to Say? There are even books that promote the idea; The Hidden Life of Trees, The Secret Life of Plants and What a Plant Knows. And here I was thinking that plants are just dumb organisms with no intelligence.

Plants are certainly fascinating and we have lots to learn about how they function, but do they really communicate? Can one plant pass along a message to another plant? Can that second plant receive the information and understand what it means?

Plant Communications - Can Plants Talk to Other Plants?
Plant Communications – Can Plants Talk to Other Plants?

What is Communication?

At the heart of this discussion is the word communication. Without agreeing on its definition we can’t have an intelligent discussion about plant communication.

Communication is the act of transferring information. It involves at least one sender, a message and a recipient. Merriam-Webster defines it as “a process by which information is exchanged between individuals through a common system of symbols, signs, or behavior.” They define “individual” as a person, but that is too narrow of a definition; animals certainly communicate.

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The key point in communication is the “exchange of information”.

Inherent in the definition is the idea that both the sender and recipient understand the message.

This is the currently accepted definition of the word “communication”, according to leading English dictionaries.

You are walking down the street and someone across the street waves their hand to you. Both you and the sender understand this to be a form of greeting, a nonverbal way of saying hi. The two of you have communicated with each other.

Now say that you were traveling in some foreign country and you wave to someone across the street. They just stare at you wondering what is wrong. In their culture the act of waving an arm in the air has no meaning. The recipient does not know if you are just stretching, catching a fly, or you’re a bit crazy. There is no exchange of information and therefore no communication. The fact that you can raise your hand and wave it, does not constitute communication.

Let’s have a look at another example. A dog pees on a bush to mark it’s territory. Another dog comes along, smells the pee and recognizes it as pee from another dog. The recipient knows that this is someone else’s territory. This is a form of communication since the message was understood by both the sender and recipient.

There is an important aspect to this communication: intelligence. Without it, the sender can’t craft the message and the recipient can’t understand it.

You are walking down the street and see someone on the other side. You could wave, but you can choose not to. You could waved in a highly exaggerated manor, or maybe just give a thumbs up. You have lots of choices, which is due to your intelligence, and each option is a different message.

How Do Plants Communicate?

There are many claims for plant communication. I won’t look at the details of these claims, but here is a brief description of some of the things science has discovered.

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An insect lands on a plant and takes a bite of the leaf. The plant reacts by producing stress-signaling chemicals. Some of these move through the plant causing other parts of the plant to produce a natural pesticide which will discourage further feeding by insects. The stress-signaling chemicals are also excreted by the leaves and float through the air. If they reach another plant, that plant may also produce natural pesticides which discourage foraging by insects. The claim is that the first plant communicated the insect danger to the second plant.

Plant roots produce specific exudates (chemicals) that cause mycorrhizal fungi to connect with the roots. The connection between plant root and fungi only happens in the presence of these chemicals. The plant communicated with the fungi and gave it permission to initiate contact – a kind of invitation to a party.

Plants are even able to communicate with insects. When caterpillars chew on the coyote tobacco plant, it sends out insect-calling chemicals that attract specific predators that come and feed on the caterpillars.

There is now some evidence that flowers produce more nectar when exposed to certain sounds that are similar to a buzzing bee, leading some to claim that flowers can hear the bee coming. Is this a form of communication between bees and flowers?

Plants may even be able to sense the difference between their own root, a siblings root and unrelated roots, through the use of chemical exudates. Roots have a sense as to who is communicating with them.

Keep in mind that much of this research is lab based. There is limited proof of these systems in the wild although some will probably occur. A more important unanswered question has to do with their importance in real world situations.

Do plants Communicate?

Consider the above example of a plant sending out stress-signaling chemicals in order to warn other plants that predacious insects are in the neighborhood. On the surface this looks like communication.

What happens if the plant is totally isolated from all other plants? Does it still produce the stress-signaling chemicals? The answer is yes. The production of these chemicals is involuntary. When insects bite leaves, chemical reactions take place which leads to the production of stress-signaling chemicals. There is no planning or thought process involved. The plant does not even know if another plant is nearby. It also can’t decide which type of wave to use. The plant is not warning another plant. The whole process can be described by simple chemicals reactions; “A” happens, then “B” happens, then “C” happens.

If you are walking down the street with no one in sight, and you wave, are communicating? Not according to our definition.

Don’t get me wrong, what plants do is still a phenomenal process that is the result of some complex evolutionary development, but it all comes down to simple chemical reactions. There is no thought process, no planning and no intelligence.

Some still claim that this is enough to be called communication, but consider this.

You are sitting in a room completely blindfolded. I come in and place an open bottle of perfume in the opposite corner of the room. A few minutes go by. You suddenly smell the perfume. You react! You might like the smell, or you might hate it. You wonder, is there someone else in the room? Did a flower just open? What is the message?

What has just happened?

The bottle of perfume is a liquid. Chemical reactions took place to release stress-signaling chemicals into the air. They moved through the air until they reached your nose. Chemical reactions took place in your nose, which caused a chain reaction of more chemical changes that eventually reach the brain.

If you compare the sequence of events for both the perfume bottle and the plant, you will notice that they are very similar. The chemicals are different, but the process is the same.

Did the bottle of perfume communicate with you?

If you say no, then you must also conclude that the plant didn’t communicate.

If you think the bottle of perfume communicated, then you are wrong, at least by our definition. Communication requires the presence of a message and intelligence to formulate the message. You might interpret the smell in a certain way, but the bottle of perfume did not craft a message for you. Neither the perfume nor the plant has created an intelligent message.

Solving the Issue of Plant Communication

When people are told that plants don’t communicate because it doesn’t follow the accepted definition of communication, the response is predictable; “plants use a different form of communication, but it does not mean they don’t communicate.”

Rather than accept the fact that their belief is incorrect, these people want to redefine the term communication.

Granted, if you redefine communication you can say plants communicate, but then you also have to accept the fact that a bottle of perfume also communicates. If you understand the plant communication mechanisms discovered so far, you will be hard pressed to come up with a definition that does not include perfume, without explicitly excluding it.

Some people have started to understand this and are using terms like “bio-communication” and “plant communication”, to distinguish what a plant does from standard communication. That is certainly acceptable.

Redefining terms to fit incorrect beliefs is neither acceptable or productive. It just confuses discussions and makes it more difficult to understand the real world.

Plant Intelligence

What is the harm in using the term communication to describe what plants do?

The problem is that it does not stop with the miss-use of one word. It quickly blows up into stupid statements like this one, “Plants release volatile chemicals into the atmosphere – these can be viewed as a language in the sense that a plant releasing the chemicals can be viewed as ‘speaking’.” Now they have their own language and can speak.

How do you say “wtf” in marigold?

The problem is that communication infers intelligence, and as soon as people accept that plants communicate, they also start believing that plants are intelligent.

There are already enough dumb beliefs floating around, like the earth is flat and planting by the moon works. We don’t need another another one!

 

If you want to leave a comment and disagree with my conclusion, feel free, but include your definition of “communication” in the first sentence. Without a definition, there is no point commenting. If you have a scientific reference that shows real communication, I’d love to see it.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

16 thoughts on “Plant Communication – Can Plants Talk to Other Plants?”

  1. The philosophical difficulties raised can be sorted out by acknowledging that “communicate” can refer to a variety of actions, including the intentional sending of information, unintentional sending of information, one-way communication, two-way communication, the mere transfer of energy (the flame communicates heat to the boiler), mere potential physical passage between contiguous areas (communicating rooms), etc., etc., etc. Clearly these are all very different, some requiring intelligent agency, others not; some transferring ordered information, some transferring potential information, some transferring no recoverable information. The bottom line of Robert’s thesis is “plants can’t think.” And indeed there is no reason whatsoever to believe that the can.

    Reply
  2. Hello Robert,

    I appreciate your efforts and would like to take the time to address a point you make.

    > “If you think the bottle of perfume communicated, then you are wrong, at least by our definition. Communication requires the presence of a message and intelligence to formulate the message. You might interpret the smell in a certain way, but the bottle of perfume did not craft a message for you. Neither the perfume nor the plant has created an intelligent message.”

    Certainly I am no expert in perfumery, but I do have a small pouch filled with sample-sized vials of perhaps a dozen fragrances from a couple of small perfume houses. I do think they communicate messages from their creators; indeed, they are very deliberately marketed as such. For example, My favorite fragrance, Bat* by Zoologist, literally smells like a rich mineral cave inhabited by bats (although some folks online have complained that it smells like rotten banana to them!).

    Perfumes are carefully blended so that the literal composition of scents is blurred and transformed into an ineffable something greater than the sum of its parts. As with other designer goods, the goal is not merely to sell you a product but a symbol about “who you are,” or perhaps a role you wish to perform. The small perfume house Ava Luxe, for example, describes one of its creations as a “devilishly sexy love potion to satisfy your inner vixen.” Another small perfume house, Imaginary Authors, designs each of its fragrances as books, complete with cover art and elaborate author biographies and historical consequences.

    The point in mentioning all of this is that it is completely valid to say that a perfume is communicating a message generated by its creator. Every perfume creator will tell you as much. Granted, this is a form of communication that involves imagination, interpretation, and a sense of storytelling, but I cannot think of any human communication which does not.

    I also find myself at odds with your argument that a plant is incapable of intelligence simply on the basis that its ostensible mode of communication is through an involuntary reaction. The weaker point against this is that many modes of communication are involuntary, such as the groans and cries we release when we are injured or otherwise experiencing an extreme sensation. The stronger point is that everything you could say about the mechanistic and involuntary nature of plant expression and communication (if they are indeed such) could also be said about all lifeforms, and indeed requires that we discuss the philosophical question of the nature of free will, and namely how we could have it, when we appear to be governed entirely by natural causes.

    It occurs to me also that if one plant produces a gas involuntarily in response to a stimulus, even if we bracket the question of whether this constitutes an expression or communication in itself, it is nevertheless remarkable that other plants can recognize the meaning behind this expression with such consistency that they have evolved mechanisms for reacting to impending threats before they happen. It is perhaps inappropriate to say that plants “deliver” messages, but clearly they “receive” them loud and clear.

    *The original formulation–I have not smelled the newer one

    Reply
    • So if I craft a perfume, and you smell it, you will know which message I am sending?

      I really doubt that. because everyone perceives the fragrance differently. how can you argue that we will all get the same and correct message?

      Reply
  3. HRH Prince Charles talks to his plants at Highgrove apparently. Which leaves me wondering whether they have ever talked back to him 😉

    Reply
  4. Interesting article. While I don’t consider trees intelligent (I think any reasonable definition of intelligence needs to include novel response to stimuli), there’s certainly a distinction between the perfume and the tree. The tree is reacting to specific environmental triggers, whereas the perfume is entirely passive. Perhaps it’s more accurate to call the tree’s behaviour chemical signaling.
    It’s notable that the word communication is frequently used to include things that don’t meet your definition – particularly in biology the need to “understand” the message is often discarded, at least in common parlance. I think you’re correct that a different word is needed.

    Reply
  5. A possible definition of communication is that information is passed purposefully from one place to another. For example, when you stub your toe, the pain receptors in your toe send a signal through your nervous system to your brain, which then acts on it. To my mind, your toe has just communicated with your brain. It has deliberately passed information.

    I think it’s a similar situation when an insect chewing on a leaf causes the leaf to send a message to the rest of the tree, which then acts on it by producing insecticides. The leaf has communicated with the rest of the tree.

    The interesting thing here, though, is that that communication also goes to the roots of the tree and is carried by the mycorrhizal network underground to other trees and plants that are part of that network. So that message that originated with the leaf is now being acted upon by neighbouring plants. Information has been deliberately passed from the leaf to the rest of the tree and to other plants. (“deliberately” may be a stretch here, but what other reason would the tree have for sending that information to its roots).

    The NY Times just published this, which may interest you:
    https://www.nytimes.com/interactive/2020/12/02/magazine/tree-communication-mycorrhiza.html
    It talks about the research done by Suzanne Simard of UBC into the interactions between trees. Although it’s not communication, it’s quite interesting how trees pass resources to one another.

    Reply
    • But has the toe “deliberately passed information”? It does not have the intelligence to do anything deliberately (defined as “done consciously and intentionally”), which implies there is intent and planning. The reaction in a toe is a set of chemical reactions that will happen each time the toe is stubbed. Using your definition the stubbed toe would not be communication because no information was passed “purposefully”.

      Reply
      • I see your point, but the pain receptors are there for the purpose of communicating that message to the brain, so that message is being sent purposefully. The pain stimulus happens in the toe and the brain hears about it. To me that means there was communication between the toe and the brain. And the purpose of whatever the toe does is intended to let the brain know – whether that is a built-in automatic unconscious chemical function or a deliberate conscious function is immaterial, a purposeful message was sent and received.

        Anyway, I’m not too invested in my argument, so I’m happy to concede the point. I do enjoy your articles and find them refreshingly clear and rigorous. Keep up the good work. 🙂

        Reply
  6. The problems are that people think of plants as not responding to anything other than light, water, gravity, and nutrients, so any transfer of what’s taken as information needs to be commented on, and that when you go to comment English doesn’t have a word for “responding to signals unintentionally sent by other individuals.”

    Reply
  7. What about moth orchids, who are designed to fool the insects to mate with them and involuntary then get covered with pollens? Disguising/dressing up oneself to attract opposite sex is a form of communication.

    Human dress up all the time. How about someone sitting in a bar and in a revealing outfit and makeup? If that can be considered passing a signal..or communicate.. so does the Moth orchid.. near about exactly the same.

    Reply
    • Moth orchids are born that way – it is the only way the flowers develop. A person sitting at a bar has decided to dress a particular way, at a particular time. It is a decision, which may be different next week. No intelligence by the moth orchid.

      Consider a flat stone where birds like to sit. Is the stone communicating with the birds?

      Reply

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