There’s a growing interest in some areas of the scientific community with the concept that plants, although not equipped with neurons or brains, are nevertheless capable of cognitive processing. For gardeners, it’s also an interesting issue because it raises the question of whether, much like humans have psychiatry to help us thrive in the world, there are ways that we might be able to help our plants thrive by being attentive to their, for lack of a better word, psychology.
What plant psychology might look like on the ground (if you’ll pardon the pun) and how we might apply it to grow better gardens is more than a speculative endeavour. Understanding how plants, for lack of a better word, “think,” has all the potential to make us better at caring for them. But first, let’s go through why the idea that plants think isn’t as wild as it initially sounds.
In a 2020 article in the Journal of Comparative Psychology, Umberto Castiello explains that plant behaviour was included in comparative psychology texts until 1935. After that point, the inclusion of plants in discussions of cognitive behaviour falls by the wayside. That, Castiello argues, is a mistake, because there’s mounting evidence “that plants can communicate, remember, decide, and even count, all abilities that one would normally call cognitive if they were observed in animals.”
Evolutionary ecologist Monica Gagliano also speaks to the limitations we put on our understanding of plants by assuming them to be incapable of intelligence simply because their anatomies differ from the ones we associate with intelligence (i.e. animal anatomies that include brains and neurons, i.e. our own).
Gagliano tells Radiolab, “we are under the impression or I would say the conviction that the brain is the center of the universe, and—and if you have a brain and a nervous system you are good and you can do amazing stuff. And if you don’t have one, by default you can’t do much in general… It’s a very biased view that humans have in particular towards others.”
What Do Plants Think About?
So what can plants do without brains? Turns out, a lot. In the Radiolab episode, Gagliano explains her experiments with mimosa pudica plants, which curl up when threatened. Gagliano’s work demonstrates that plants can identify threats, learn when something is not a threat and remember that lesson for at least 28 days.
Castiello runs through some of the evidence for various other cognitive abilities in plants. These abilities are amazing. There’s evidence that plants communicate with other plants via “plant to plant chemical messages.” Research has found that they can recognize kin and grow more or less competitively depending on whether their neighbours are related to them or not. Studies going back to Darwin show that climbing plant tendrils “tend to assume the shape of the surfaces they have already come into contact with; that is they learn progressively the shape of potential support characteristics.” They’ve even been determined to make decisions about growth based on perceptions of risk.
Ecologist Suzanne Simard has done seminal work on how trees communicate with each other through fungal networks in the soil. In an interview with Yale E360’s Diane Toomey, she explains that trees send resources to each other and warn each other about threats regardless of whether neighbouring trees are related or not (although they can send resources preferentially to their own kin). Simard says that the evidence she’s gathered suggests that “it’s not just resources moving between plants. It’s way more than that. A forest is a cooperative system.”
How Does This Help Us as Gardeners?
When we understand that plants grow and behave with intention, we can better plan our gardens with an eye to how our plants might respond. We might really, really want a plant to live in a particular corner, but if they learn that resources are better a little further down the garden bed, we can expect to find their roots reaching out in that direction.
We tend to think about our plants individually, or as families who usually compete with other non-related plants. Research about plant cognition suggests that plants might work together more often than we think.
Castiello points to research that suggests that plants and trees will work cooperatively during times of water stress, transferring resources or signaling to other plants, whether competitors or not, “to adopt water-saving behavior that would, at the end of the day, benefit both” plants. Thinking about how plants think might urge us to consider our gardens as communities that help each other, even if it happens in ways we don’t understand.
This more ecological approach to gardening might lead us to think about our gardens holistically. We might take better account of the soil in our growing practices, and be more careful to nurture the soil ecosystems that help our plants to thrive.
In the End
In the end, thinking about plants as thinking beings might simply make them seem more relatable and therefore more worthy of our ethical regard. “If we can relate to it, then we’re going to care about it more,” says Simard. “If we care about it more, then we’re going to do a better job of stewarding our landscapes.”
So the next time you feel like you’ve become too eccentric because you talk nicely to the plants in your greenhouse, keep in mind that they are probably responding. They’ll just take longer to do it than the family dog.