How long will Juglone be present in the soil after a black walnut tree has been removed? I want to plant some new trees in that location. Thanks
Kent County Michigan
A study has shown that juglone toxicity (the substance walnut trees secrete) lasts for at least two months in the soil after the tree is removed but it has also been shown that decaying walnut tree roots can release juglone into the soil for several years. There are a large number of trees, shrubs, vines and plants that are resistive to juglone toxicity though that you can plant in the area where a black walnut tree was. Just Google "plants resistive to juglone" and you will get a long list
Juglone is found in all parts of the black walnut tree, but it is most concentrated in the flower buds, nut hulls, and roots. Unfortunately, the roots of a black walnut can extend three to four times the diameter of the tree’s canopy and squirrels and other animals will disperse the nut hulls across an even more far-reaching range, so the area affected is quite wide. Toxicity is further dependent on the soil’s texture and drainage.
Definitive testing has not been done and the effects can vary from soil to soil and plant to plant. Juglone sensitivity is also dependent on other growing conditions so it's hard to say for certain which plants will be affected and which will be fine. However, tomatoes seem to be the most sensitive to growing under black walnuts. Other species known to be affected include alfalfa, some apple varieties, rhododendron, white pine, white birch, eggplant, pepper, lilac, cotoneaster, and privet, among others.
The best advice when gardening near black walnuts is to use caution. If possible, locate gardens or landscape beds away from the root zone of the tree. Well-drained soils apparently present fewer toxicity problems than poorly drained soils. Avoid mulching garden areas with walnut leaves or nut husks. Root barriers to prevent walnut roots from advancing into garden areas may be helpful. If you choose to plant near the tree, your best bet is to create raised beds with some type of screening on the bottom, to prevent invasion by black walnut roots. Also, be careful that nuts and debris from the black walnut tree don’t accumulate on the raised bed. As an added precaution, make sure the soil in the raised bed is well-drained. Good drainage seems to lessen the effect of the juglone.
This article lists vegetables sensitive to juglone:
Depending on the size of the walnut tree, the roots typically reach 2-3 times farther than the tree is high. The strongest influence is within 50 feet of a mature tree. The following guide discusses juglone breakdown, and how far you should locate your gardens from the tree.
I hope this helps. Thanks for using our service.
Thank you so much for this great information!!!!
This article says that Norway Spruce are affected. The second article mentions ginkgo.