Allelopathy: The Secret Language of Plants
Published: 2025-05-22Tags: алелопатия, растения-компаньони, другаруване, пермакултура, устойчиво земеделие, съвети за градинари
Translation
This is a translation of a Bulgarian-language post. It conveys the content faithfully but is not the author's original English writing.
In nature, plants do not merely coexist — they communicate with one another through invisible chemical signals that can change the fate of the whole garden. This phenomenon is called allelopathy and is a key factor in the balance, competition and symbiosis of the plant world.
pole beans and corn in the "Three Sisters"
Back in 2007, when I first heard of permaculture, I was very impressed by the Native American "Three Sisters" garden and its "companion crops" (that was the term with which I translated for myself the English expression "companion plants").
"Plant guilds" and the literal "companion plants" were also used later in Bulgaria, and with these community-born terms we called the plants with allelopathic properties. The word "allelopathy" caught up with me much later. I remember that then I looked up its etymology and was even more impressed. I share it with you too:
The word "allelopathy" comes from the Greek words állēlos (ἄλλήλων), meaning "to one another" or "mutually", and páthos (πάθος) — "suffering", "illness" or "strong sensitivity"!
It resonated with me at once!
What is allelopathy?
Allelopathy is a biological phenomenon in which one plant releases biologically active substances (allelochemicals) that affect the growth, development, survival or reproduction of other plants around it. These substances can be released through the roots, the leaves, the bark, or during the decomposition of plant residues.
The influence can be either positive (stimulating) or negative (suppressing) — accordingly we speak of positive and negative allelopathy. In most cases, however, the effect is negative and is used as a form of defence against competitors, pests and diseases.
How does allelopathy work in the garden?
Even if you have never heard of allelopathy, you have probably noticed that some plants do better together, while others get in each other's way. A classic example is carrots and onions — planted next to one another, they protect each other from pests. Conversely, tomatoes and potatoes, although relatives, often fall ill and suppress each other's development if they are close together.
Examples of allelopathic interactions:
Black walnut releases juglone — a substance that suppresses the growth of many other trees and vegetables, including tomatoes and potatoes.
Carrot and onion mutually protect each other from pests — the onion drives away the carrot fly, and the carrots repel the onion fly.
Garlic and aubergine help each other and grow better together.
Coriander repels the Colorado beetle, which attacks potatoes and aubergines.
The "Three Sisters" trio (used by the Native Americans of North America) — corn, pole beans and squash — where the corn serves as a support for the beans, the squash covers the soil and protects against weeds, and the beans fix nitrogen in the soil.
Cereal crops such as rye and wheat suppress weeds through allelochemicals, which are retained in the straw and the mulch.
Allelopathy as a tool for sustainable agriculture
Although known since antiquity, in recent years allelopathy has been used more and more actively in organic and sustainable agriculture. By combining suitable crops, we can eliminate the need for herbicides and pesticides, limit weeds and increase yields.
Mixed sowings (e.g. corn, beans and squash) use allelopathic properties for mutual protection and better uptake of resources.
Cover crops such as rye, sunflower and buckwheat suppress weeds and improve soil fertility.
Legumes enrich the soil with nitrogen and support the growth of neighbouring crops.
Practical advice for gardeners
Always check which plants are good neighbours and which get in each other's way. Avoid planting plants of the same family next to each other, or one after another in the same place.
Use plant residues for mulch carefully — some can suppress the following crops.
Try crop rotation and mixed crops, to make use of the positive effects of allelopathy.