Walnuts close to fruit trees

[Haus]

I have two walnuts next to my main orchard. I just cut one down, but does the jugalone come from the roots? Or does it stay in the soil for some time? Any way to successfully get trees planted where there once was a walnut standing?

 

[sagittarius]

Yes, Yes, and maybe. The one good thing about walnuts, they tend to kill any nearby buckthorn. Buckthorn seems more sensitive to the juglone than most other trees/bushes. Juglone is activated by air, both in the soil and leaves and walnut husks on the surface. It does break down over time, the walnut husks seem to be the biggest source of Juglone.

 

[chickenlittle]

Juglone is a bit complicated to nail down. Some think that there are factors such as soil type and things as to how much effect it has and how long it takes the juglone to break down and not cause harm. I'd think you'd be in good shape within a couple years of killing the tree.

I had some apples that I transplanted fall of 2018 after cutting some walnuts down that spring. I'm not positive it was juglone but all of those trees had declined by late spring 2019. I lost a few and transplanted the rest back to a good spot. They are still struggling the following year.

 

[Hoytvectrix]

During my postdoc, I did some work on allelopathic plants. Jugalone, like most other allelochemicals, has a relatively short activity in the rootzone. I'd say a season after removing any of the walnut husks and/or living tissue should be mostly free. Most allelopathic plants have a continuous production of the allelochemical simply because the allelochemicals are designed to be mineralized and mobilized in plants.