Kitchen Garden Forum

Has anybody ever heard of this? I was reading on a website today that there is something in their roots which causes plants under their shade to die.

I take things posted on many websites with a pinch of salt but some years ago I organised a communal snowdrop planting in grass under some walnut trees in our local park and out of the hundreds of bulbs in the green planted only handful so far seem to have made an appearance or have survived.

Fact or fiction?

I've never heard of it, but I have only seen one, in Norfolk when camping on a farm, took us a while to work out what it was with those big soft green fruits.

Find it rather hard to believe. Some gardeners come up with some strange theories why their plants don,t thrive

There are few plants that repel competition like elderberry but I don't know anything about walnuts.

I wonder if this has always happened but now just more obvious due to the changes in the climate & lack of trees? Potentially in times gone past maybe something else also grew there that wasn't affected?

A few quotes from Googling.
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What Is Allelopathy? Allelopathy is a biological process involving one plant completely stopping the growth of a neighboring plant in order to further its own growth.
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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.
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Most all allelopathic plants store their protective chemicals within their leaves, especially during fall. As leaves drop to the ground and decompose, these toxins can affect nearby plants. Some plants also release toxins through their roots, which are then absorbed by other plants and trees.
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Some plants and trees those are well known as allelopathic are Black Walnut (Juglans nigra), Ailanthus or Tree-Of-Heaven (Ailanthus altissima), Fragrant Sumac (Rhus aromaticus), Rice (Oryza sativa), Pea (Pisum sativum), sorghum etc. Black walnut is an expert allelopathic plant which contains allelopathic properties within its leaves, buds, roots and nut hulls, it is also known to secrete a substance into the soil called juglone that is a respiratory inhibitor to some plants.

Thanks very much for that info Geoff.
I had no idea such a word as Allelopathy even existed so we always learn something new on this forum!

I wondered whether walnut poisoning was just another "old wives rales" when I saw it quoted on a website somewhere but ir seems from what you,ve discovered there,s a real possibility thwt my snowdrop planting project under walnut trees in our park could possibly have been deterred by this impact. After all, they,re very small bulbs so may surcombe quite easily to local toxins.

You,re never too old to learn something new!