Allelopathy is the biological term for plants having a (usually negative) impact on other plants growing close by by producing one or more biochemicals. The main time that we hear about allelopathy is when it comes to walnut trees or Eucalyptus . Though there are a number of other plants which can also act on their neighbours in detrimental ways.
I am not a scientist, but I am fascinated by these plant interactions. And working out the relations between different plants is, of course, an important part of my design work. It is sometimes important to think about allelopathy when designing a system. The intricate world of plant interaction is something we know surprisingly little about. But what we do know can help inform our planting decisions.
One important thing to remember about allelopathy, is that the biochemicals released by a particular plant will effect only some types of other plant. So you can find suitable neighbours even for walnuts and other famed ‘bad companions’.
Of course, plants can also have a positive effect on one another. We can refer to these beneficial interactions as probiosis, or perhaps symbiosis or mutualism where both plant communities benefit, and commensalism when just one benefits and neither suffers. Plants can often benefit their neighbours, acting as ‘nurse plants’ for example. And we are also learning more and more about these interactions as time goes on and seek to create synergistic systems.
This is an intriguing area, which combines known science, anecdote and empirical observation from growers around the world. I do not claim to be an expert on the science, but I have built up a catalogue of effective plant combinations through my own experiences in my own gardens, and through my design work. I find it fascinating and I am constantly seeking to learn more.