Marlene Dietrich, in her strong German accent, said this in the old movie ‘Grand Hotel’, but plants say it too, in a silent deadly way. Nature has a way of giving certain plants an advantage over the rest. They contain an unfriendly substance that prevents other plants from growing underneath. They want to be alone.
The word allelopathy comes from two Latin words, allelon meaning ‘of each other’ and pathos which means ‘to suffer’. Allelopathy is the chemical inhibition of one plant to another. The chemical can be in the roots, any part of the plant or even in the soil where it affects the growth development of other competitors. Sometimes it means the plants are aggressive enough to crowd out the competition.
Plants already compete for sun, water and soil nutrients and, like animals, even for territory it seems. Their allelopathic qualities are actually controlling or limiting their surrounding environment causing other plants to decline if they are unlucky enough to seed or be planted too close.
Most commonly, California walnuts trees, Juglans californica and Juglans hindsii , and any walnut tree really, have allelopathic effects on plants growing beneath them. The substance produced by walnuts is called juglone. (Ain’t Latin great!)
Other trees with allelopathic traits include Bearberry, Oaks, Sycamore, Manzanita California Bay laurel, Cottonwood, Forsythia, Tree-of-heaven, Black locust and Eucalyptus. In my garden, oaks and manzanita, Arctostaphylos viscida, are the ones needing their space, so I don’t plant anything under their canopies.
California chaparral plants, like Brittlebush, Encelia farinose, Purple sage, Salvia leucophylla, California sagebrush, Artemisia californica, and Chamise, Adenostoma fasciculatum have been known to be allelopathic. However, botanists now know that bare zones under chapparal plants are caused by animals seeking cover and, basicly “eating at home”
In the garden, when you discover a tree or shrub is resisting any plants growing underneath, you can begin to work with nature. Raking under a tree or spreading mulch to add neatness can help blend these areas into your scheme. You no longer have to fight it, but plant outside the drip lines of these difficult characters.
Note: If you have eucalyptus and white fly problems you are in luck! Covering the ground, underneath a white fly infested plant, with eucalyptus bark will clear up the problem like magic. After chopping down a Euc, and when the bark on the logs began to dry and flake off, I happened to use the bark as mulch under a hibiscus (this was in Fullerton…Southern California). It had had a bad case of white fly, but after a few months it was completely gone!
List of plants for around oaks and pines
I found this fascinating! I had not heard of allelopathic plants although I do know that here, nothing grows under gumtrees and, as far as I knew, the soil beneath them is rendered barren for years after the trees have been eradicated.
Oooh…I may have to source some Eucalyptus bark this summer. We had a bit of a white fly problem last year. I’m curious to see if that would help.
I used to be a firm believer in the allelopathy gospel until I ran across a review by Rick Halsey of the scientific literature on the subject in Torreyana. If you have access to JSTOR you can read it at: http://www.jstor.org/pss/4126940. (Even if you can’t access it, the abstract at the bottom of the page is a good summation.) I’m not a scientist, but I actually found it pretty easy going and incredibly eye-opening. There are lots of empirical observations that would support allelopathy, and you’ve shown lots of situations I’d consider evidence of it. Some authors even considered that some plants emit gases that inhibit competition. But Halsey’s paper shows that opinions are actually a little more mixed, and I’m trying to stay open minded and out of the way of the more heated debates. Maybe a safe place to hide out would be in the grass-free area under a spreading oak, whether the bare earth came about through allelopathy or some other form of successful competition…
Thanks, Desiree, I had eucalyptus in Southern California where it grows widely and the grass slowly died underneath.
Clare, I hope it works if you do this. It was a happy accident for me.
Hi James, yeah, there is controversy. That paper, used as one source for this post, written to refute an earlier claim by botanist, C. Muller, that chaparral plants were allelopathic, would be interesting to discuss sometime. My personal observations here are that not much grows under eucalyptus (at my former home) and manzanita. I’m no botanist, though!
Oops, missed the fine print citations at the end… Whatever the reasons for the barren patches, the patches are real!