The greening of vacant lots can reduce self-reported feelings of depression in adults. In a Philadelphia study of 324 participants living in an area where 110 vacant lots received clean-up and greening interventions, the number of participants self-reporting feelings of depression decreased by 41.5% after vacant lot greening.
South EC, BC Hohl, MC Kondo, JM MacDonald, and CC Branas. (2018). Effect of Greening Vacant Land on Mental Health of Community-Dwelling Adults: A Cluster Randomized Trial. JAMA Netw Open 1(3):e180298. https://doi.org/10.1001/jamanetworkopen.2018.0298