[oldman]

The poison part is the chemical in the leaves that causes the same reaction as poison ivy or poison oak. The spice is kind of like mace in that it's a thread structure between the seed and the flesh of the fruit. The plant is related to cashews and there are a few dozen varieties of sumac, including smooth sumac like Lisa's weed. I'm not sure how much fruit you'd need to harvest to get a useful amount of spice or which species are useful.

I'd recommend buying some of the spice and cooking with it before you try growing it. It's lemonish tart, but not a bright lemon flavor. Muted and flat, but not metallic or astringent.

You aren't going to plant horehound in your yard if you've ever tried to get rid of it or tasted it. ;-). No reason to put in sumac if it's not that useful, it's going to give you a rash, and it will be extra work to get rid of it.