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Can plants kill other plants?

We all know that some plants can be toxic to humans, causing skin rashes, stomach upsets etc. We are all told as children not to eat the fruit  of some.

My question is: can some plants release toxins into the soil, which kill woud be competitors? I'm not talking about parastitic plants like mistletoe, which can poison their hosts, but those which release toxins into the soil. For example, we had a yucca which I dug up for no other reason than that it did not flower and we did not like it. For eighteen months now, nothing has grown within a meter and a half of the stump, even weeds.

I have looked this up and found very little on the subject, though I do remember reading an article about the Arizona desert some years ago, which said that some cacti were toxic to others. It will be useful to find a list of plants which had such properties and were best avoided in the garden.
Everyone likes butterflies. Nobody likes caterpillars.


  • chickychicky Posts: 10,379
    Walnut trees are known for sending out toxins that stop anything else growing in their canopy ☠️
  • BenCottoBenCotto Posts: 4,293
    “A dictatorship is like a giant beech tree - magnificent to look at in its prime but underneath nothing will grow.” Stanley Baldwin.

    Rutland, England
  • I think the term for this type of chemical inhibition of other plants is allelopathy and here is a website I found with a brief explanation and a few plants that are known for it are listed.
  • pansyfacepansyface Posts: 21,924
    Apophthegm -  a big word for a small thought.
    If you live in Derbyshire, as I do.
  • The short answer is: yes. There are quite a range of allelopathic plants: walnut, sunflower, sycamore, ferns, pine, dodder (a parasite), knapweed , garlic mustard, catalpa, Tree of heaven (Alianthus) and propably many more, but little research has been done. There are two broad types: general allelopaths, which kill a wide range of other plants and specific allelopaths, which kill only certain species.
    Fortunately very few native British plants are allelopaths. There seem to be a lot more in N America and the Tropics. Probably a number of conifers, apart from pine, are allelopaths, but the evidence is circumstantial based on the fact that coniferous woodland has a much sparser understory than broadleaf. Other factors, such as lack of light and dry soil, complicate the issue.
    Thank you for your comments on this little-studied subject.
    Everyone likes butterflies. Nobody likes caterpillars.
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