I have used it for years because slugs love, love love hostas. It has to be UNUSED COFFEE. It is the caffeine that attack their nervous system. I know coffee is expensive but I do not drink coffee and when I travel they give it to me free in the hotels.
Just so everyone is aware the used coffee grinds from Starbucks already brewed will not give you the results you desire. Used coffee grinds is good for compost but it will not do anything fo slut control.
