Are you sure it's black horehound? It may be henbit (Lamium),which is a common weed that prefers rich,moist soil.I think some people use it as a groundcover,although there are numerous varieties of this species that are much more attractive.

I believe it IS henbit! (Or purple deadnettle.) It has a strong odor when crushed. The bumblebees love it, but I don't.

I have henbit coming up alot in my gardens too. (Columbus area).

I don't think I'd want it as a ground cover! If it's cousin are the pretty lamiums - well, I like them.

...Beverly

Henbit is less invasive than ground ivy,but I have both of them in my yard. They seem to thrive in partly shaded,wet areas so they are loving it here! I think the ground would still have adequate moisture if it didn't rain for another month.