Last summer we lost a huge black walnut tree in a storm. This transformed an incredibly shady area into a perfect site for a new raised bed veggie garden,which is something I really need since my entire yard is quite shady. I wonder about the soil though-that walnut tree had been growing on that site for at least 50 years-I've had hostas and a few other shade loving perennials growing underneath it. When I put in my new raised beds I will be adding fresh soil, but my question is, do I need to put some kind of barrier down to keep the black walnut toxins (juglone?) from affecting my new veggie plants (I won't plant until next year)?
Sorry I can't give you a good solid answer, though I have heard that juglone is water soluble and that if you compost the leaves, they should be safe after one year.
I'd be concerned about how well the soil would retain the juglone.
Many veggies are tolerant and you might go that route; corn, beans, pumpkins, squash, etc. You can do a search for juglone tolerant plants online.
Those of the nightshade family are at a high risk and should not be planted; tomatoes, eggplants, peppers, etc.
I would think that if your bed was eight to ten inchs deep, you shouldn't have any trouble. I wouldn't be afraid to try it. Anytime I build a new get I layer the bottom with a heavy layer of news paper. It helps to keep grass from coming up in the bed and after a few years, it rots.