I planted some arborvitaes along my property line against a neighbors driveway. They have horses in the field across the driveway so the trees and the animals are not necessarily close. However my neighbor is worried that if her horses escape the fence they may find the arborvitaes and she claims they are toxic for her animals. I would like to be neighborly and move them or fence them off, however I would like to confirm how toxic they are to horses so I can determine what level of mitigation is required. Thanks, Stephen.
Howard County Maryland
We found that NC State University and the University of Idaho both list Arborvitae (Thuja sp.) as potentially toxic to horses.
This question is outside of our area of expertise though, so I would recommend contacting a specialist in horses if you have further questions about it. Here is a link to the UMD horses program, https://extension.umd.edu/horses