Stopping horses

With reference to Shaun Cooper’s letter about witches stopping horses [ FT361:74-75]: when I was a child my mother told me of a wise woman/witch in Somerset in the late 1800s called Old Mother Wembridge, past whose cottage horses refused to go if she was standing in her doorway. Drivers would get down and ask her to go inside. She would do so, laughing, and only then would the horse move on. Since then I read somewhere of a plant that horses dislike, and I wonder if Mother Wembridge perhaps used it in making her remedies and horses could smell it on her person. Elsa Beckett London