Allelopathy: Can Plants Communicate?By Barbara Pleasant | 7 October 2021
Plants have a hidden language that allows them to communicate with each other. This phenomenon, known as allelopathy, was first described in 1937 by Austrian botanist Hans Molisch as “The Effect of Plants on Each Other.” Over the past 80 years, this idea has evolved, with scientists now understanding that plants communicate chemically through volatile organic compounds (VOCs) released by their roots, stems, and leaves. These VOCs can serve as messages that influence the behavior and growth of neighboring plants.
One common example of allelopathy in action is companion planting, where gardeners pair certain plants together, often assuming they understand how plants interact. While we may not fully comprehend the details, we know that some plant combinations thrive, while others struggle. For instance, parsnips and summer leeks are known to work well together both above and below ground.
Effective companion planting relies not only on root compatibility but also on above-ground communication, primarily through airborne molecules. As stationary organisms, plants rely on these gaseous signals to convey vital messages. This form of communication is very direct, akin to human speech, but in a plant’s case, the messages might include “Stay away,” “I’m being attacked by insects,” or “You’re welcome here.”
Recent research has revealed fascinating insights into how plants use VOCs to both promote their own survival and warn their neighbors. For example, a 2006 study explored how the parasitic dodder plant uses VOCs to locate its preferred host plants. In controlled experiments, dodder was consistently able to find tomato plants, while avoiding less suitable wheat, based on the chemical cues emitted by the plants.
Plants also seem to communicate for mutual benefit. A study involving crimson clover showed that it produced more VOCs when planted alongside orchard grass, nearly doubling its output compared to when it was grown alone. This indicates that diverse plant communities often produce a broader array of VOCs, fostering greater communication among plants.
In fact, plants may even prefer the company of other species. A 2009 study on lupine seedlings demonstrated that plants grown with non-related neighbors performed better than those grown with their genetic siblings. This finding supports the idea that plant diversity promotes healthier growth, possibly due to the richer mix of VOCs produced in diverse environments.
Interestingly, research has suggested that we could potentially harness this chemical communication to improve plant health. A team of Bulgarian scientists investigated the effects of plant extracts on tomatoes. They found that extracts from carrots, dill, parsley, and onions had noticeable impacts on tomato growth. For example, onion extract reduced tomato growth by 30%, while carrot extract boosted it. In a different study, carrot seed-based sprays helped pea plants grow more vigorously and even controlled weeds.
Another example of harnessing plant communication is the practice of “aromatherapy” for plants. Spraying basil tea on tomato plants has shown to enhance growth, mimicking the benefits of planting basil and tomatoes together. Similarly, Mexican mint and basil sprays have been found to support healthy growth, serving as natural plant boosters.
In conclusion, whether through direct companion planting or by using plant-based extracts, we are engaging in a form of communication with our plants, speaking their chemical language. It’s a form of interaction they rely on for survival, and understanding it can help us foster healthier, more productive gardens.