Pecan shells contain juglone, an important plant compound with strong allelopathic properties.

If you store it for few months, stirring frequently, the juglone will dissipate. It can also be addedl to the compost pile. If you wish to use it fresh....small amounts only scattered at the surface.

Agree partly with Rhizo.

The allelopathic property is more pronounced in Black Walnut. Juglone is an oil that can persist in soil for a long time, even after the tree is removed. I would not add it to any garden soil or compost. There are plants that are not affected by it but them some like tomatoes are very sensitive to it.

Thanks for the info probably just won't use them

You can always spread them out on an area that is weedy - not in the vegetable garden as others have said - but in weedly unplanted areas they work great to improve the appearance.

Dave

I don't know that juglone qualifies as an oil.

Dave has the best idea....use the hulls on an area where there are no plants of any kind. That's probably even true for the finished compost, if you want to be safe. There are a jillion lists of juglone sensitive plants....each seem to be different from the others. Best to be cautious.

Pecan shells are an expensive but attractive mulch used in my area but mainly in perennial beds, not vegetable gardens. I would use them in an established garden area.