What is allelopathy?

Allelopathy literally means “death to others.” In its simplest sense, allelopathy is the ability of one plant species to affect the growth of another through their chemical exudates. While early researchers narrowly defined the relationship to include only the influence of living plants on other living plants, more recently the definition has been expanded to include interactions within the soil environment. Such “soil-mediated chemical interference” is arguably a more relevant definition, as roots of adjacent plants share the same soil environment. Competition for water and nutrients, soil microbial activity, and other environmental conditions should be considered separately from any possible “chemical warfare” among plants. Therefore, allelopathy is currently understood to involve living or dead plant parts that release chemicals into the soil which have an effect on other plants—positive or negative. And no allelopathic chemical is better known—and feared— than juglone.

Read this interesting treatise on juglone and its history as a bogey for poor plant performance by Linda Chalker-Scott –

Do Black Walnut Trees Have Allelopathic Effects on Other Plants?

And once you have had your myth revealed, check out these other horticultural myths that Chalker-Scott and team have worked over:

Horticultural Myths

Image: Impatiens struggling, think it's the juglone?