The concentration of the chemical - a natural plant hormone called juglone - is greatest in the hulls and shells. So I would suggest not using it. It does dissipate over time as exposure to air oxidizes the chemical and eventually renders it pretty much harmless, but still not something I would want in an actively growing garden. Might be a pretty decent mulch for bare areas to keep weeds away, however :-)

And the effect of this hormone is not uniform. Some plants react to it more strongly than others and with many plants, it has no effect at all.

OK, thanks. I need to find more info on which plants are less affected. The suggestion to use it as mulch in some other (weedy) area is a good one.

Black walnut or other? You can research "juglone resistance" with plenty of success at finding research based lists.

Thanks, rhizo_1. I thought I would ask here first as I like this place and talking with real people. I don't know what kind of walnuts I have, somebody gave me a whole bunch at Christmas in the shell.

Those would most likely be English walnuts, as those tend to produce large and tasty nuts and are what are most commonly sold when you buy walnuts. And while they still produce juglone, they do not produce it with the same intensity as black walnuts, which are natives and the trees most commonly encountered and generally considered to be the most problematic.

And with the quantity of the shells you are dealing with, I'm not sure I'd be too worried about putting them anywhere.....except maybe directly on a vegetable garden. Unless the "whole bunch" you were gifted with at Christmas produced a cubic yard or so of shells :-)