Walnut shells

I've been given a couple of wheelie bin loads of organic walnut shells from work as well as leftover pressings in another bin.
I was just wondering if anyone knows if they will have any allelopathic effect on my trees or garden?
I would like to use the shells as mulch around trees and work the pressings into a bed that might have some greens in a few months.

Hey Andy,

Yes walnut shells contain a juglone precursor that breaks down into juglone over time, and are therefore allelopathic. There does seem to be big differences in juglone concentration by species of walnut, but this study has some more specifics on plants that were found to be affected, and the long and short is that most anything you plant under this mulch (including greens) will be strongly affected.

That can be a resource though! Use them in a gravel driveway if you have concerns about grass coming through, along paths to keep them clear, anywhere you want to limit growth.

They make good tinder.

Some people use them in/in place of cat litter, though I think it has to be ground for that. Would probably help keep litter fresh in a chicken coop as well.

If you make biochar, the shells would work as a feedstock. The juglone doesn't have much effect once the shells are pyrolized, according to this study.