On Plant Intelligence

How do we define intelligence?

If you google the word, it’s simply defined as “the ability to acquire and apply knowledge and skills”. Underneath this definition, Google lists similar words, mind, brain, reasoning, and understanding.

When we look at animals, this definition becomes a little different. With animals, the purpose of knowledge and skills is less conceptual than ours, instead, it is about survival. The avoidance of danger, and the desire for survival, at a fundamental level, is something that can define intelligence. 

There is not a creature alive that does not contain some level of adaptability when it comes to its safety. Look at a cheetah that bolts away at the slightest sign of a threat or a bird who flies away at the same. Even an amoeba, one of the simplest forms of animal life, will move away from a dangerous heat source if it feels it is in danger.

If we see these behaviours as a form of intelligence, then how are plants any different?

Plants make decisions based on their survival. Of course, it’s not based on the same central nervous system animals have, and therefore it looks very different. Animals’ survival instincts operate on a time frame of seconds and minutes, but plants’ instincts work over days and weeks. However, does this mean the base of intelligence is really that different?

Plants grow their branches and canopies to adapt for survival. They even communicate with other plants through chemical signals sent through their root networks interconnected by mycelium – known as the “mycorrhizal network”, which we’ll be covering later on. 

Plants sense their environment much in the same way that animals do. While they don’t have the same central nervous system animals use to create these responses, those responses are still there.

In this article, I would like to explore several different experiments surrounding plant intelligence and allow you to form your own thoughts on this controversial subject. 

Do plants truly have intelligence, or is this not the right word? Is there a real application for the unique way in which plants interact with the world? Should we view our plants as mere products or as partners instead?

I hope to put forth a new perspective on plant intelligence that will put your job as a grower in a new light. Hopefully, this will help forge a deeper connection between you and the plants in your care. 

Experimenting on Plant Intelligence

There have been numerous experiments done that show plants’ unique ability to interact with the world. I’ll be briefly going over these experiments to showcase the versatility of plant intelligence, and the powerful systems found within our photosynthetic friends.

Plants as Bio-Sensors

First, there was a 2002 experiment that sought to use genetically engineered plants for tactical systems applications. Plants were genetically modified with a green fluorescent protein found in jellyfish to emit light when contact was made with blue or UV light. This modification made it so that plants could be used as sort of environmental sentinels, able to covertly detect explosives, as well as biological and chemical warfare agents. 

What this experiment shows us about plant intelligence is that plants have incredibly sophisticated methods of interacting with their environment. Albeit, this experiment relied on human modification of the plant's genetic makeup, so it could be argued that the GFP was responsible for the results, as opposed to the plants themselves. 

However, the second experiment we’ll be covering shows plants in their natural state being used for a similar purpose. This experiment was conducted in 2011 and was designed to show how plants could be used to detect TNT in the soil that they were planted in. The experiment used a type of shrub (Baccharis halimifolia), which was planted in soil containing varying levels of TNT. Over 9 weeks it was found that the plants had measurable responses to the different concentrations of TNT. 

Low TNT contamination could be determined by an improved physiological response based on the increase in nitrogen found in the soil. Higher levels of TNT instead induced stress in the plants. This experiment determined that TNT-contaminated plants could be identified separately from their unaffected counterparts, showing that plants could effectively detect TNT within the soil that it’s planted in. 

Now, again, is this intelligence, or simply humans noticing a plant's basic response to physiological conditions? Can we go as far as to say that a plant exposed to a toxic substance is intelligent for becoming stressed? While it may seem easy to say no, in the process the plant has provided us with valuable, potentially life-saving information through its physiological processes. While the plant itself may not be conscious of it, through its sensitivity to its environment, the organism has provided us with knowledge we would not have had otherwise.

This concept of a plant being in tune with its environment is where the strongest arguments for plant intelligence lie. Take our third experiment for example, which showed plants’ sensitive responses to contact with insect larvae' footsteps. In this experiment, cryo-scanning electron microscopy showed that insect larvae with uniquely hooked feet leave footprints on a plant. 

Again, it’s easy to say that these plants are merely being damaged by the larvae' feet, which is why footprints are left. It’s what the plants do in response to this damage that is truly fascinating. Once damaged, the plant begins superoxide production, in a process called thigmomorphogenesis, which is how plants respond to mechanical stimuli. In this case, this response prevents pathogen infection, and thus protects the plant from further damage. It’s astounding that a plant can experience a stimulus so minor as the footsteps of an insect larva, and respond with the necessary processes for self-preservation.

Plant Intelligence in an Ecosystem

While these bio-sensor experiments are all fascinating, perhaps none of them highlight a plant’s intelligence as much as how plants behave in an ecosystem. There are two phenomena I’d like to cover here, first are tri-trophic interactions, and second, are how forests act as a community. 

Tri-trophic interactions are the interactions between a plant, an herbivorous insect, and the predator of that insect. When a plant realizes it is under attack by an herbivore, it will emit what is called an Herbivore-Induced Plant Volatile. These essentially attract predators of the herbivorous insect to come take care of the problem. 

This process demonstrates a plant’s ability to not only sense that it is in danger, but take genuine action to address the threat. While, yes, the plant is not necessarily aware of these actions, it is still addressing and responding to the negative stimuli of an insect attack. 

Next, we have the complex mycorrhizal network found underneath the forest floor that interconnects tree roots with each other. This is a symbiotic relationship trees have with networks of mycelium underneath the forest floor that connect with their roots. 

Tree roots exchange carbon with the mycelium, while the mycelium brings nutrients nitrogen and phosphorus into the root system from the soil. Aside from nutrient exchange, these networks also allow trees to share nutrients and communicate, specifically with members of their species. 

Within mycorrhizal networks there is a process called “kin recognition”, wherein trees show higher levels of interconnectivity with members of their species. In some cases, different species of trees will share the same mycorrhizal network, which is thought to improve the overall resilience of the forest. 

Trees primarily use mycorrhizal networks to send excess nutrients to each other, as well as using something called allelopathy to send chemical signals that may alert each other of imminent dangers. Trees use allelopathy to better defend their species as a whole against predators, or invasive species. 

Similar to tri-trophic interactions where plants will emit chemical signals to attract beneficial predators, trees will send chemical signals to each other as warnings of imminent danger. This shows that trees not only have built-in defence mechanisms to protect themselves but their community as a whole. 

So, are Plants Intelligent?

Taking a look at these experiments and concepts as a whole, consider for yourself whether or not plants truly have intelligence. What’s so fascinating about this for me is that there really is no correct answer, and your perspective depends on what metrics are being used. 

Is environmental sensitivity a form of intelligence? Can intelligence be defined by an organism's ability to convey information? Can intelligence be measured by the systems an organism uses to survive?

These are all questions you’ll have to answer for yourself. 

Regardless of your opinion on these matters, we can all admit that plants are sensitive, living creatures. This brings us to the question of our roles in the lives of these organisms, and the concepts of plant empowerment, parenthood, and partnership.

Empowerment, Partnership, and Parenthood

Plant Empowerment is a concept promoted by a Netherlands-based organization pushing for the optimization of growing practices by becoming more in tune with the plants themselves.

As growers, it is our natural instinct to try and boost production methods by any means necessary, whether or not it’s what plants naturally desire.

Plant Empowerment focuses on the plant’s balances. These balances are water, energy, and assimilates. The philosophy at play here is that plants that grow more in tune with their natural state will make optimum use of nutrients, and be more naturally resilient to pests and diseases. Plant Empowerment implies that instead of relying on treatments to make your plants resilient, they will do this naturally with the right support from their growers. 

What this ultimately speaks to is that plants make decisions about how they will grow based on their environment. By automatically assuming plants are not resistant to pests and diseases, we take away their agency in the growing process. Instead, by having a sort of dialogue with our crops, we can allow plants to be self-sufficient when possible, and we can step in to care for them when necessary.

When these plants’ balances are out of equilibrium, they will react in a way that ultimately harms the crop as a whole. If a plant is in a state where it needs to focus energy on creating secondary defensive metabolites, for example, its fruit will not be nearly as tasty, or bountiful. 

As we’ve covered in the experiments above, plants are highly sensitive beings that have built-in responses to the environment around them. As growers, we have a responsibility to understand and respect these processes. This brings us to the concept of Plant Partnership.

Remember that in your greenhouse, the operation would not be possible without the cooperation of your plants. While it may seem like your plants are simply the product you’re producing, in reality, they’re closer to being your thousands of silent business partners.

By viewing plants as living beings with needs and desires, and understanding that your actions will garner reactions from them, you can do a better job of working alongside them to have the best harvest possible. 

Take a plant with some older leaves, for example. The plant will naturally begin putting more energy into growing new leaves and will put less energy into defending the older ones. This makes these older leaves more susceptible to both pests and diseases, and the plant will waste its energy keeping these leaves alive. By stepping in and removing the older leaves, you’re setting your plant up for success, so you can have a more fruitful relationship moving forward. 

As a grower, by understanding the needs of your plant – where it may need assistance, and where it doesn’t – you can form a working, give-and-take relationship that will create tastier fruit and more bountiful harvests.

If you view your plants as mere objects, you’re more likely to fall into the trap of giving them a set amount of light, water, and fertilizer, and expecting them to grow perfectly. This is not how it works. You need to have an open dialogue with your plants to understand how they are responding to certain stimuli, and to optimize your operation for their growth. 

While plants are your partners in the venture of growing food, in reality, the relationship is maybe most similar to parenthood. 

When you have your seedlings, these plants are like infants. You have to take care of them when they get sick, feed them the right balance of nutrients, sing them lullabies every night – OK, maybe that last one isn’t necessary. However, you have to do pretty much everything for them, and if you give them the proper attention, they will grow up accordingly. 

However, in mid-season, your plants may become moody teenagers. You may feel like you’ve given your plants the perfect balance of care and affection, and yet they still won’t grow the way you think they should. At this stage, plants may act like teenagers texting at the dinner table, completely ignoring their parents.

Plants, eventually, of course, grow into adults who you can have a more productive relationship with. This is where your patience and effort as a plant parent are rewarded, as they begin to produce fruit and finally become, so-called, productive members of society. 

Unfortunately, the plant life cycle is much shorter than humans, so your plants won’t be able to care for you into your old age. Instead you will have to continue taking care of them in their final days. You will inevitably have some senior citizens under your care at the end of the season, and there comes a point where palliative care and death are necessary to start the cycle anew. 

How do you see your Plants?

The point of this article wasn’t to convince you that plants are super intelligent life forms. Instead, I want you to consider their capability as independent beings with their own unique way of interacting with the world. 

I believe this territory is largely unexplored, and as growers, we have the opportunity to work alongside plants and use their intelligence to improve food production as a whole. 

Think of how you interact with your plants, and what they are trying to tell you. How can you work alongside them to create a more meaningful partnership and fruitful relationship? 

The next time you aren’t getting the results you want from your crops, I challenge you to see them as independent beings and to have an open dialogue with them about their needs. 

And how can you  communicate with them, you might ask? By continuous measurement and monitoring. You won't be able to personally tend to every single plant at all times but technologies like what we developed here at ecoation will allow you to do a pulse check and have a dialogue with a large group of individuals under your care. 

Like a sports team, your greenhouse needs daily huddles and strategy planning. Communication is the key and your plants themselves will tell you what they need to play their best game! 

I leave you with this final question — do you simply see your plants as a product you’re producing, or as partners in your mission?

If you’re interested in reading more about this fascinating subject, I have three books to recommend for you. First is What a Plant Knows, by Daniel Chamowitz, and second, The Revolutionary Genius of Plants, by Stefano Mancuso. Finally, if you want to learn more about the mycorrhizal network covered earlier, and the complex ways forests operate, The Hidden Life of Trees, by Peter Wohlleben is another terrific read.