There are myriad things you can toss into a compost bin, like vegetable trimmings, eggshells and even almost all nutshells. One big exception in the nutshell category: walnut shells. Turns out walnut shells can be lethal and toxic to plants because they contain high concentrations of juglone, a compound produced by some plants to stunt the growth of other plants. Juglone is so effective as a plant toxin, it is sometimes used as an herbicide. If you toss walnut shells into your compost and use the finished compost in your garden, you could inadvertently be killing your crop.
ANDREWS MCMEEL SYNDICATION