Are Plants Intelligent?

Are plants intelligent? Are they able to communicate with each other? Do they remember experiences? Do they have emotions? And why does it matter?

There is increasing research into the topic of plant intelligence and some startling findings are emerging. I would like to take you through three main facts that point towards plant intelligence.

How do we define intelligence? Well three of the key things that we humans do to function so successfully are; communicating, remembering and we have emotions.

Plants can communicate

We don’t often hear plants talking to each other, but I often don’t hear the people I’m texting either. Right now, there are radio signals flying through the air which are encoded with information. There are many forms of communication – even in this speech, my body language is a way of communicating in addition to the words I’m saying. Wolves communicate by leaving urine marks on the ground to act as chemical signals to tell all the other wolves that, “This is my territory.”

Just like wolves, plants also use chemical signals to communicate. Each plant has its own chemical signature which they release into the air through the pores in their leaves. Plants can change the chemical signature that they emit in order to communicate a specific message.

An example of a plant’s message was studied in Limpopo in the late 1980s; During a drought, the Acacia tree was one of few trees remaining for Kudu to eat. Surprisingly, dozens of kudu started dyeing without any signs of predation or sickness. Autopsies could not identify why the kudu died – until the stomach contents were studied. The kudus died due to elevated levels of tannin in their stomach. Tannin slows down the digestive process. Tannin is a chemical found in the Acacia plant, but Kudus can tolerate normal levels of tannin just fine. What scientists found, was that some Acacia trees were being overgrazed, so the trees released a chemical into the air to warn nearby Acacia trees that ‘predators are coming’. The trees that received the signal, increased the levels of tannin in their leaves – which is what killed the Kudu. This study kick-started the investigation into plant communication and many other examples have been studied since.

We don’t know if a plant communicates with every other plant, or with specific plants. We don’t know if they receive a reply since wind is their main mechanism of transferring messages. We don’t know why a plant would so selflessly protect other plants. However, we do know that there are messages in the air that we haven’t decoded yet...

Plants can also remember

Plants are able to remember experiences that they’ve had and respond accordingly.

In a state of the art laboratory in Germany, researchers allowed a pea plant to germinate and grow towards the sunlight, as any plant would do. The plant was clearly skewed towards one direction. The researchers then stuck the plant in a fridge for one night to put it into a dormant state. When they took it out the fridge, they placed it in the sunlight, but with the growth direction facing away from the light. Now usually a plant would turn towards the sunlight, but for several days this plant kept growing away from the sunlight... The plant remembered in which direction it was growing before it was put in the fridge, and continued growing in the remembered direction until it realised that the sunlight was no longer in that direction.

On a warmer example, during the day a Sunflower follows the sun to keep its nectar warm, since bees prefer warmer nectar to colder nectar. The Sunflower turns back during the night so that it is in the right orientation for the sun in the morning. How does it remember where the sun is going to be in 10 hours time? I’m not sure if I could point to where the sun will rise tomorrow. When the plant is young it learns where the sun will rise, and it uses this memory to find the sun overnight.

If plants can communicate and remember, it would not surprise you if I told you that

Plants have emotions

Plants respond to direct and indirect stimuli with emotions – just like we do.

Many of us will have heard of the music experiment, where you play classic music to one plant, and heavy metal music to another plant, and you compare their growth. Overwhelmingly it is found that the plant with classic music grows better. How can this be? Just like how classic music calms me, and heavy metal stresses me, so do plants feel the same emotions. This is an easy experiment that you can get the kids to try at home.

There is a plant in my garden with small leaves that closes its leaves at night time and opens them again in the morning. It closes them to sleep. In Japan, researchers prevented this plant from sleeping by simulating 24hr sunlight. Conventionally, we would think that the more sunlight a plant gets, the faster it will grow. However, after a few days, the plant turned yellow and died. It is believed that, like humans, plants get tired and rely on night time to rest. Also similarly to humans, we don’t actually know what being tired really is, nevertheless, it is a familiar emotion to all of us.

So we’ve seen that plants have intelligence, so what does it mean? It means that we need to look at plants in a new light. They are much more like us than we thought. Perhaps their chemical signals have an effect on us? Perhaps they can heal us? Many of us have felt how depressing it can be to walk through a degraded environment, but we’ve also felt how invigorating it can be to walk through a pristine forest. There is definitely more to plants than what meets the eye.

Plants can communicate, remember and feel, so let’s look at them like never before.

Himkaar Singh