"Could my walnut trees have killed other plants nearby?" This is a question we often get from people who bought trees and shrubs from us that died when planted near Juglans nigra. When you sell as many plants as we do, this happens sometimes (and we replace them under guarantee so all is not lost, dear customer!)
To the Latin scholar chemists amongst you that should tell you all you need to know. For the rest of us it might be a mystery unless you are lucky like me and happened to see an information leaflet on the stand of Hadlow College who were strutting their stuff at the Chelsea Flower Show.
I must admit I "sort of knew something" about black walnut's ability to kill other plants but the students of Hadlow made it very clear. Black Walnut is called Juglans nigra in Latin. Juglans is the root (no pun intended) for juglone which is an allelopathic drug. That means it stunts or kills. And black walnut is the biggest natural producer of juglone, which it uses to great effect to kill unrelated plants and trees nearby. If you have a black walnut and trees and shrubs relatively close to it suffer wilting, yellowing foliage and either die or stop growing, now you know why. Incidentally, juglone is probably one of the reasons that black walnut is so resistant to Honey Fungus.
So here is (as the Americans would say) - the take away. Mother nature likes balance, so there are a number of plants that don't mind juglone and can be planted near your black walnut. They include:
Acer negundo (Box Elder)
Acer palmatum (Japanese Maple)
Acer rubrum (Red Maple)
Acer saccharinum (Silver Maple)
Betula pendula (Silver Birch)
Betula nigra (Black or River Birch)
Catalpa bignonoides (Indian Bean Tree, Foxglove Tree)
Cornus Mas (Cornelian Cherry)
Cydonia oblonga (Quince)
Gleditsia triacanthos (Honey Locust)
Liquidamber styraciflua (Sweetgum)
Liriodendron tulipifera (Tulip tree)
Picea abies (Norway Spruce)
Prunus serotina (Black Cherry)
Pyrus calleryana (Pear)
Robinia pseudoacacia (Black Locust)
Tilia platyphyllos (Broad leaved Lime)
Of course, we sell a fair selection of the above, if you are interested.....
Relax and enjoy watching your garden grow!
Death by Black Walnut by Julian de Bosdari is licensed under a Creative Commons Attribution-Share Alike 2.0 UK: England & Wales License.
Based on a work at blog.ashridgetrees.co.uk.