Background Vacant lots are often overgrown with unwanted vegetation and filled with trash, making them attractive places to hide illegal guns, conduct illegal activities such as drug sales and prostitution, and engage in violent crime. There is some evidence that greening vacant lots is associated with reductions in violent crime.

Methods We performed a randomised controlled trial of vacant lot greening to test the impact of this intervention on police reported crime and residents' perceptions of safety and disorder. Greening consisted of cleaning the lots, planting grass and trees, and building a wooden fence around the perimeter. We randomly allocated two vacant lot clusters to the greening intervention or to the control status (no intervention). Administrative data were used to determine crime rates, and local resident interviews at baseline (n=29) and at follow-up (n=21) were used to assess perceptions of safety and disorder.

Results Unadjusted difference-in-differences estimates showed a non-significant decrease in the number of total crimes and gun assaults around greened vacant lots compared with control. People around the intervention vacant lots reported feeling significantly safer after greening compared with those living around control vacant lots (p<0.01).

Conclusions In this study, greening was associated with reductions in certain gun crimes and improvements in residents' perceptions of safety. A larger randomised controlled trial is needed to further investigate the link between vacant lot greening and violence reduction.