Composting breaks down the juglone and isn’t a real issue unless perhaps if the compost is all walnut debris. The shells themselves, however, can take years to break down.

tj

Walnut fruits - husks, shells and nut meats - contain the highest concentrations of juglone. But all can be neutralized by composting. The hard casings - husks and shells - take time to compost fully so make sure they are chopped up as best you can before adding.

Wear gloves while you're handling Black Walnuts. I wouldn't put the shells in a compost pile for both reasons. They're like wood and if you're compost isn't 100 % efficient you stand the chance of losing or damaging your plantings.

Must be some method of using them to effect the growth of weeds in say a mulched slope that's too steep to plant on, or in a stone bed.

Good idea! But not Effect.

The opposite.

Suppress.

I think that was supposed to be 'affect' but I agree suppress is a better term.

I'm using walnut planer shavings as mulch in garden paths. I'll let you know if it actually suppresses growth. I should think the husks or leaves would be better though.