Allelopathy is a process by which a plant releases chemicals that can either inhibit or benefit other plants. Since most allelopathic plants cause harm to other plants, that’s the what I’ll be discussing here.
Species competition ensures the biodiversity of ecosystems. All plants and animals have developed techniques for out-competing other species for nutrients, water, territory, and other resources. For example, certain plants have extremely dense root systems.
Allelopaths are plants that have an advanced weapon in their arsenal. The allelopathic plant competes with other species through “chemical warfare” by releasing chemicals that inhibit the growth of its competitors.
Allelopathic substances work like herbicides, preventing the germination and growth of the seedlings of competing species. Plants that are under stress, such as those with pests, diseases, or less than optimum access to nutrients, sun, or moisture, are at an even higher risk for being eliminated by allelopaths.
Depending on the plant, allelopathic substances can be released from a plant’s flowers, leaves, leaf debris and leaf mulch, stems, bark, roots, or soil surrounding the roots. Some of the chemicals biodegrade over time while others can be persistent in the soil.
Probably the most well-known allelopathic plant is the black walnut (Juglans nigra) tree. All parts of the tree–roots, bark, leaves, nuts, and even rainwater that falls off a leaf–release an allelopathic substance called juglone. Some species are affected by it and others aren’t bothered at all.
My great-aunt used to have a huge black walnut tree in her yard. I always thought it was bare underneath because we kids were always playing and horsing around underneath it! Maybe that was part of it, but the juglone must have been at work as well.
If you’re wondering what to grow near your black walnut tree, try serviceberry/juneberry/shadbush (Amelanchier sp.), tulip Shasta daisy (Leucanthemum x superbum), speedwell (Veronica sp.), or American arborvitae (Thuja occidentalis), or one of many others. More information about plants that are affected by juglone, and those that are not, is available here.
Other common trees with allelopathic properties include eucalyptus, sugar maple, tree-of-heaven, hackberry, southern waxmyrtle, American sycamore, cottonwood, black cherry, red oak, black locust, sassafrass, and American elm.
Allelopathic study is in its infancy, but early research suggests that allelopaths can be used as effective herbicides for organic weed control. For example, an allelopathic crop might be used to control weeds by planting it in rotation with other crops.
I wonder if organic herbicides based on allelopaths are commercially available, or will be soon. It’s interesting to think about the possibilities of allelopathic chemicals for the organic gardener.
Photo courtesy of Wikipedia
How about Neem oil and pyrethrins? Do they qualify?
I learned about the Black walnuts when I first moved to PA – pretty amazing what plants learn to do to ensure their future generations!
I really appreciate the suggestions for things that can be grown under the Black walnuts… for now, whenever I plant a new tree, I try to give the walnuts a wide berth!
This is great, Caroline. I’ve been interested in companion gardening since reading “Roses Love Garlic” some years ago.
Nature provides everything we need…we just need now to rediscover secrets like this one.
Interesting question Ginger. I can’t tell for sure but it seems that neem and pyrethrins don’t qualify as allelopaths because the substances they produce kill insects not plants. But still good examples of natural ways of “pest control.” Now if they could only discover a “deer-lelopath.”
JLB, I’m reading about “plant guilds” in a book on permaculture. Plant guilds are groups of plants that work and grow together synergistically. The walnut/hackberry guild is the most interesting because of the presence of juglone. It also includes currants, chiltepine, wolfberry, and even peppers & tomatoes!
Hi Michelle, I haven’t read Roses love Garlic yet though it’s on my (long) list. There are so many natural synergies, some tested and others untested, but there is a lot that our ancestors knew about growing that we don’t because we have come to rely too much on easy solutions like chemical preparations.
This is really interesting. I don’t know much on this topic, but am wondering a few things.
1) If allelopathic herbicides kill plants, then how will the plants you want to grow not die?
2) Will this be the new development with genetically modified plants? Could the next generation of corn have allelopaths in the genetic makeup so that farmers will not dump a gagillion pounds of herbicides? Oh wait, that would just be efficient.
I really need to get my gardening game on again soon. Since I’ve left the farm over the summer, I’ve forgot about this world. Hopefully, since I’ll be moving out of my house I can hopefully have a yard and some time to experiment. Thanks for the post!
Hi Matt, good to “see” you again. Good questions all. 1) Researchers don’t know exactly why but there are some plants that are able to resist the allelopathic substance. It must have something to do with competition & evolution but no one knows exactly why.
2) I think there is a Monsanto corn in the works that will have an allelopath that kills non-Monsanto corn. KIDDING! But doesn’t it seem like something that could be true? I have not come across any research on this but allelopaths do seem like something that someone would try to squeeze into a GMO species.
By the way, I downloaded your research paper on sustainable agriculture and I’m looking forward to reading it. Thanks for making it available. And good luck with getting a new place and getting a garden going.
Garden Green Garbanzo Beans never require the use of insecticides because of a natural plant acidity. Insects will not bother the plant. They are allelopathic by nature with germination inhibitors keeping the pure garbanzo lineage dating back 7,500 BC.
Green Garbanzo beans are a natural allelopathic plant, never requiring the use of insecticides, having a highly acidic composition, they are one of the healthiest, safest foods on the plantet. Annually renewable and a nitrogen fixing legume plant, never depleting the soil such as grains, corn, potatoes. etc.
I happened upon your interesting site and was enjoying the reading and info. I then read the entry by this doug moser character. Unfortunately I visited his site. This is arrogance and misinformation at its worst. Chickpeas or garbonzos as some call them are somewhat allelopathic but are usually attacked by armyworms which can destroy up to 25% of a crop. It’s sad that he is using this site as a way of advertising his own product especially when misleading people. He also claims that insecticides will never need to be applied to a growing crop. What about seed treatments, grass herbicides, and fungicide treatments. I know people who grow garbonzo beans and they need to apply these chemicals so that the crop can survive. doug mosers claim on his web site of his product being organically grown is an out and out lie. I appologize for the negativity but this guy is leading people to believe untrue statements.
Hi Jay. Thanks for your comment. When I got those comments from Doug, I was honestly torn between taking them down because I didn’t appreciate that he was using my site as advertising, and leaving them up because of supporting a small farmer. I don’t know anything about chickpea farming so I can’t validate his claims. I will say that it is possible to organically grow chickpeas–there are several brands available–and I don’t believe that chemicals must be used for crop survival.
But regardless, I think that I should go with my instinct about not allowing people to post advertisements on my site. That’s really not the purpose of my blog. I decided to leave Doug’s comments posted but I took down the links to his site.
I want to known that, is the plants of Cucurbitaceae family Allelopathy in nature ?
Hi Ahire, I have not heard or read anything that indicates Cucurbitaceae (includes gourds, cukes, pumpkins, squash, watermelons, melons, etc.) have allelopathic properties. It’s probably possible but it certainly doesn’t seem to be common in the family. I’d be curious to hear your experiences.
Hey caroline, i heard that hair works to fend off deer, im not sure where this came about, but its worth a try on a small section- just scatter the hair all the way around the perimeter- hope for the best, plan for the worse, and remember your tool box when heading to the field. Soil science -painfully seeking out the amazingly obvious
Cheers!!!!
Hi! I’m doing a lab on the allelopathic affects of alfalfa on rye, clover, and radish. I was just wondering if when the allelopathic chemicals from a plant that is edible get on to another plant that is edible, will this second plant still be edible?
Thanks.
Read my book on Homoeopathy for Farm and Garden, where these issues are discussed.
to be found at considera.org or narayana-verlag.de
I knew about back walnut for many years. I suspected black cherry for a very long time. Now I have confirmation of what I expected. No garden vegetables will grow under their canopy, nor in the region 10 to 15 feet beyond.
Thank you Caroline.
Nik
I am having trouble getting any type of flowers to grow under my Yoshino cherry tree is it an alleopathic tree or any suggestion. thank you
Hi Carolyn
I’m not finding much info about red oaks, every time I search I come back to the same sites about walnut. I just moved my potatoes from my regular garden, as they would appear to be incompatible with everything I wish to plant into that garden, just under the drip line of my red oak tree! Does this mean I will have to move them again???
I found in several places that blueberries love to be under oaks, what about strawberries?
I’m having a hard time finding a tree compatibility list to go with fruits and vegetables, my yard is almost completely shaded by the neigboring trees. I have a crabapple, two cherries and a red oak to contend with in my lawn.
Thank you for taking time to anwser my questions, concerns.
blueberries would love being under oaks b/c oak leaves are super acidic and blueberries thrive in acidic soil. The acid soil could explain why some plants don’t work under the oaks too. Strawberries like acid soil, so do potatoes. What state do you live in? Try this–google search on “plant communities” and the name of your state. you might be able to find a list of plants that work well together in your area.
Hope this helped a little! Let me know what you find.
I’m in Iowa, central Iowa actually. I’ll do the plant search and see what I come up with thank you for your help.
Hello Carolyn,
I live in Victoria, Australia and have recently been affected by the Black Saturday fires in February. I want to try and protect my home and farm by planting fire resistant/retardant plants and trees. I’d like to use exotics (and some natives)that feed the soil rather than some of the natives that seem to attract fire and are allelopathic. There are natives that are legumous, that can be used for fodder as well as wind and shelter breaks, which I have collected seed to propagate, but I don’t know enough about allelopathy, and need to find out more. I want to create shelterbelts which have as many species(native and exotic) as possible, compatively. Of some of the burnt trees in front of our home, one is an old oak tree, that seemed to catch the embers and slowed the fire down, and has since regenerated, as did the peach tree, cherry plums, elm and a boobiallah. That is why I think mixing the types of plants and trees are important. Do you have advice on the above issues? Terrible wild fires are something that, it seems, we can’t stop, and other factors like water issues, artificial chemical fertilizers, pesticides, herbicides, have to have
a big connection. It is that knowledge that I need to feel a little safer in a future fire prone area.
Thankyou, regards, Karen.
p.s. I did’nt know about blueberries and oaks, your site is very informative.
Hi Kathy, General advice that I saw is that deciduous trees are more fire resistant than conifers due to sap in bark, needles, etc. Pine needles as mulch would not be a good idea for ex. I found some good general resources for you. But I don’t know much about native vs. exotic species in Australia so I will leave it to you to judge what is what.
Australian resources: This is a great bibliography on fires and vegetation from the Australian Nat’l Botanic Gardens here: http://www.anbg.gov.au/bibliography/fire-plants.html
And a very informative brochure with list of plants/trees from the ROyal Tasmanian botanical Gardens:
http://www.fire.tas.gov.au/mysite/publications/1709%20Brochure.pdf
Some good general advice is here, but keep in mind it’s targeted towards the US Western states: http://www.ext.colostate.edu/PUBS/natres/06303.html
http://www.edcfiresafe.org/fire_safe_vegetation.htm
http://smslrwma.org/nativeplanting/pdfs/NativePlantsForFirescapingBySDCNPS.pdf
http://www.fountaingrove2.org/OSMA/Fire_Safety/Fire_Resistant_Trees___Shrubs/fire_resistant_trees___shrubs.html
As for allelopathy specifically, you might want to check out Toby Hemenway’s book on permaculture called Gaia’s Garden.
good luck Karen! You have a big project ahead of you. Keep me posted on how it works out.
So now that I’ve read all of this, I will stop feeding black-oil sunflower seeds in the feeder right over a perennial planting plot. I’ve cleaned up as many of the hulls as I can, but it’s not possible to get all of them on a rough soil surface. How long must I wait before I plant perennials there, or do you have another suggestions to make it safe to plant perennials there?
can i just ask if iris cristata can be a possible candidate as allelopathic plants?
I have the same question–how long do the toxins stay in the soil? And if I amend it with clean soil, will that dilute it enough to let things grow under the birdfeeder? (switching to hulled seeds!)
AWESOME!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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