MASTER GARDENER: Does a plant know anything?

While most animals can choose their environments, seek shelter in a storm, search for food and a mate or migrate as the seasons change, plants must be able to withstand and adapt to constantly changing weather, encroaching neighbors and invading pests, without being able to move to a better environment.

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We tend not to pay attention to the sensory machinery in the flowers and trees found right in our own backyards.

While most animals can choose their environments, seek shelter in a storm, search for food and a mate or migrate as the seasons change, plants must be able to withstand and adapt to constantly changing weather, encroaching neighbors and invading pests, without being able to move to a better environment.

Because of this plants have evolved complex sensory and regulatory systems that allow them to modulate their growth in response to ever-changing conditions. An elm tree has to know if its neighbor is shading it from the sun so that it can find its own way to grow toward the sun.

A head of lettuce has to know if there are ravenous aphids about to eat it up so that it can make poisonous chemicals to kill the pests. A Douglas fir tree has to know if whipping winds are shaking its branches so that it can grow a stronger trunk. Cherry trees have to know when to flower.

On a genetic level, plants are more complex than many animals, and some of the most important discoveries in all of biology came from research carried out on plants.


Clearly, using the word “know” is unorthodox. Plants don’t have a central nervous system; a plant doesn’t have a brain that coordinates information for the entire body.

Yet different parts of a plant are intimately connected and information regarding light, chemicals in the air and temperature is constantly exchanged between roots and leaves, flowers and stems to yield a plant that is optimized for its environment.

Plants may not have eyes or noses or a brain to interpret sensory input with emotion, to see and smell like a human but they do react to sight and smell.

Darwin wrote, “There are few plants, of which some part...does not bend toward lateral light.” We see this happen daily in houseplants that bow and bend toward rays of sunshine coming in from the window.

This behavior is called phototropism. In 1864 another researcher discovered that blue light is the primary color that induces phototropism in plants, while plants are generally blind to other colors.

In 1880 the Darwins proved that phototropism is the result of light hitting the tip of a plant’s shoot, which sees the light and transfers this information to the plant’s midsection to tell it to bend in that direction. They had successfully demonstrated rudimentary sight in plants.

In 1918 Garner and Allard, two scientists at the U.S. Department of Agriculture, experimented on the Maryland Mammoth tobacco plant and found that when the plant was exposed to the long days of summer it would keep growing leaves.

But if it experienced artificially shorter days, then it would flower. This phenomenon, called photoperiodism, gave us the first strong evidence that plants measure how much light they take in. Other experiments followed proving that what a plant measures is not the length of the day but the length of the continuous period of darkness.


And there is Phytochrome, meaning “plant color.” In nature, the last light any plant sees at the end of the day is far-red light signifying that it should “turn off.” In the morning it sees red light and it wakes up.

In this way, a plant measures how long ago it last saw red light and adjusts its growth accordingly. How do plants know when spring has started? Phytochrome tells them that the days are getting progressively longer.

Plants also flower and set seeds in the fall before the snow comes. How do they know it’s autumn? Phytochrome tells them that the nights are getting longer. Plants must be aware of the dynamic visual environment around them in order to survive.

They need to know the direction, amount, duration and color of light to do so. Plants detect the visible (and invisible) electromagnetic waves.

Although plants see a larger spectrum than we do, they don’t see in pictures. Plants do not have a nervous system that translates light signals into pictures.

Instead, they translate light signals into different cues for growth. Plants don’t have eyes just as we don’t have leaves. But we can both detect light.

This article is a synopsis of "What a Plant Knows" by Daniel Chamovits. Next week I will write further on his research about what a plant smells and remembers. As a Master Gardener, I found most of this information new and fun to know.

It is not pure University of Minnesota Extension information but I like thinking about what my plants can tell me. This book goes beyond shade plants, full sun plants and those other aspects of what a plant likes or doesn't like in its environment.


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