Therapeutic gardens have existed for several decades in English-speaking countries, particularly North America. Sometimes referred to as horti-therapy, this mediated therapeutic activity has been developing in France over the past few years with patients suffering from mental illness. The aim of this end-of-study nursing project is to provide some theoretical keys to the benefits of these therapeutic gardens in mental health establishments: social benefits, physical benefits, cognitive benefits and emotional benefits. It also looks at the role of the nurse in this mediated activity.