September 5, 2018

Greening Vacant Lots as a Cost-Effective Mental Health Intervention in Underserved Populations

Study evaluates urban green space as an approach to public health promotion
Turning empty urban lots into green spaces appears to improve nearby residents’ psychological wellbeing, according to a recent study. The depression-alleviating effects are even greater among those below the poverty line.


South EC, Hohl BC, Kondo MC, MacDonlad JM, Branas CC. Effect of greening vacant land on mental health: a citywide randomized controlled trial. JAMA Netw Open. 2018;1(Under Review):1–14.

Study Objective

To assess whether greening of vacant urban land reduces self-reported poor mental health in community-dwelling adults


This study included 541 vacant urban lots in Philadelphia, based on their meeting of criteria for “blight”: unmaintained vegetation, trash, abandoned cars, etc. These lots were selected from a larger “Clean and Green” urban renewal project spearheaded by the Philadelphia Horticultural Society.1 The lots were grouped into 110 proximity clusters of 0.25-0.50 mile radii, and randomly assigned to 1 of 3 intervention groups:

  • Trash removal: All visible trash and discarded items were removed from the lot, overgrown vegetation was trimmed/mowed, and monthly maintenance was performed.
  • Greening: In addition to the activities above, the lots in this group were professionally leveled, lawns and small trees were planted, and short fences were installed around the lot perimeters.
  • Control: No intervention was performed at these lots during the duration of the study. (Upon completion of the study, these lots were also greened).


Urban residents living within one of the lot clusters (N=342) completed this study, which consisted of filling out a survey focused on perceptions of “urban health.” This survey was completed before the intervention and again ~18 months later, after the trash removal/greening had occurred. Participants and data collectors were blinded to the intervention (ie, survey data collection was performed independent of knowledge that the intervention in local vacant lots was occurring). Participants had a mean age of 44.6 yr (SD 15.1 yr), were 60% female, and 44% had a household income below the poverty level of $19,530.

Outcome Measures

As part of a larger survey, participants completed the self-report Kessler-6 Psychological Distress Scale (K6) before and after the greening/cleaning/control initiative. This scale measures frequency of recent subjective experience of nervousness, hopelessness, restlessness, depression, worthlessness, and effort. Pair-wise comparison of pre-post changes were made between intervention groups using intention-to-treat cross-sectional time series regression.

Key Findings

Reduction in K6 scales occurred in all groups during the 18 months of the intervention, which may reflect changes in the national economy during the study period (2011-2013, the Great Recession recovery period).

Independent of these baseline changes, there was a significant reduction in self-reported feelings of depression and worthlessness for residents living in the greening clusters compared to the control clusters. Depression was reduced by 42% (95% CI: −63.6% to −5.9%; P=0.03) and worthlessness decreased by 51% (95% CI: −74.7% to −4.7%; P=0.04), compared to no significant reduction in the control clusters. There was also a trend in the reduction in K6 composite score (ie, overall self-reported poor mental health) of 63% (95% CI: −86.2% to 0.4%; P=0.051) compared to control.

Among residents living in households below the poverty line in the greening clusters, the reduction in depression was even greater (68.7%) compared to control cluster residents (95% CI: −86.5% to −27.5%; P=0.007).

There was no statistical difference between trash removal and control cluster residents in either overall or subscale K6 scores.

Practice Implications

This is one of the first studies to employ an experimental design (ie, random assignment to variable vs control conditions) to the urban green space approach of public health promotion. Unlike previous studies in this area, the current study is able to attribute direct causation of mental health benefits to the greening vs control conditions. This very important step will allow for direct analysis of the benefits (including cost-benefit analysis [CBA]) of the intervention, so that they may be replicated, expanded, and developed into workable programs in the future. Preliminary CBA analysis of a similar study has suggested a return-on-investment (ROI) of $224 per every dollar invested.2

The findings of this study demonstrate the importance of environmental factors in influencing individual and community mental health. These effects have been known in both clinical and academic contexts as well as via direct human experience for many years.3 Most people are aware of how their surroundings can influence their mood, ability to concentrate, and outlook on life. The stimuli of our environment have direct impacts on neuroendocrine activity and corresponding affective and cognitive function.4

This may be especially relevant in modern urban environments, where the stimuli can be significantly different and more intense than a rural landscape to which we are more evolutionarily adapted.5 The “Urban Stress” theory suggests that living in cities may be inherently less healthy because of these “new” settings (evolutionarily speaking). A substantial body of evidence supports this concept.6,7

This issue is particularly concerning for underserved urban populations (ie, the urban poor). These populations have some of the worst health in the country due to a variety of factors, including limited access to healthcare; air, noise, and light pollution; crime; psycho-social stress; and increased allostatic load.8 In particular the unique combination of poverty and urban decay has been shown to directly contribute to higher rates of depression in these populations.9

It is already known that urban green space is beneficial for physical health, especially for the urban poor. In a landmark study published in the Lancet, researchers demonstrated that proximity to urban green space was not only associated with reduced mortality (after controlling for socio-economic status [SES]), but that when stratifying groups based on SES, the effect of green space was vastly more important in lower SES groups than in higher SES groups.10 For people at the bottom of the economic ladder, the “healing power of nature” can be a substantial life-saving resource.

Many studies have shown that urban green space can have positive impacts on mental health. Previous issues of NMJ have reviewed some of these studies.11,12 One approach that has been investigated for improving the health status of the urban poor is the “Urban Greening” movement that has appeared across the country. These initiatives combine the salutogenic aspects of biophilia, the concept popularized by E.O. Wilson that suggest humans have an inherent healthy affinity for natural places, with public health programs like the CDC’s now-defunct Healthy Places initiative.13,14 The Philadelphia Horticultural Society is one of the national leaders of not only Urban Greening efforts, but also collecting data to demonstrate the substaintial benefits and efficacy of their programs.15,16 By reducing urban blight and improving the local environment, it is possible to change the conditions in which health, including mental health and quality of life, are created.

One limitation of this study is the lack of data identifying urban residents’ direct exposure to the vacant lots before, during, and after the interventions. It is not possible in the current study to connect changes in K6 scores with participants’ use or appreciation of the newly greened lots. However, the experimental design of the study confers that some aspect of causation, rather than simple correlation, has occurred as mentioned above. Future studies may wish to add a measure of individual green space exposure as an additional metric for analysis, but that does not detract from the value or findings of the current study.


This study extends the idea of “medicine” beyond the level of personal impact and demonstrates that large-scale public health interventions, particularly those involving the greening of environments in which we live, work, and play, can substantially improve the mental health and well-being of a community, particularly for the most vulnerable members of society.

Categorized Under


  1. Philadelphia Horticultural Society. Clean and Green Program. Published 2018. Accessed January 8, 2018.
  2. Philadelphia Horticultural Society. Evidence of Success. Published 2018. Accessed August 29, 2018.
  3. Kaplan S. Aesthetics, affect, and cognition: Environmental preference from an evolutionary perspective. Environ Behav. 1987;19(1).
  4. Parsons R, Hartig T. Environmental psychophysiology. In: Cacioopo J, Tassinary L, Berntson G, eds. Handbook of Psychophysiology. Vol 172. 2nd ed. London: Cambridge University Press; 2000:815-846.
  5. Falk JH, Balling JD. Evolutionary influence on human landscape preference. Environ Behav. 2010;42(4):479-493.
  6. Abbott A. Urban decay: scientists are testing the idea that the stress of modern city life is a breeding ground for psychosis. Nature. 2012;490:162-164.
  7. Gong Y, Palmer S, Gallacher J, Marsden T, Fone D. A systematic review of the relationship between objective measurements of the urban environment and psychological distress. Environ Int. 2016;96:48-5
  8. Mercado S, Havemann K, Sami M, Ueda H. Urban poverty: an urgent public health issue. J Urban Heal. 2007;84(SUPPL. 1):7-15.
  9. Mair C, Diez Roux A V, Galea S. Are neighborhood characteristics associated with depressive symptoms? A critical review. J Epidemiol Community Heal. 2008;62(11):940-946.
  10. Mitchell RJ, Popham F. Effect of exposure to natural environment on health inequalities: an observational population study. Lancet. 2008;372(9650):1655-1660.
  11. Beil K. Exposure to residential green space improves mental health. Natural Medicine Journal. Published 2014. Accessed September 4, 2018.
  12. Beil K. Neighborhood green space can predict mental health status. Natural Medicine Journal. Published September 2014. Accessed September 4, 2018.
  13. Wilson EO. Biophilia. Cambridge: Harvard University Press; 1984.
  14. Centers for Disease Control and Prevention (CDC). Healthy Places. Published 20 Accessed January 8, 2018.
  15. South EC, Hohl BC, Kondo MC, MacDonlad JM, Branas CC. Effect of Greening Vacant Land on Mental Health: A Citywide Randomized Controlled Trial. JAMA Netw Open. 2018;1(Under Review):1-14. 
  16. Branas CC, Cheney RA, MacDonald JM, et al. A difference-in-differences analysis of health, safety, and greening vacant urban space. Am J Epidemiol. 2011;174(11):1296-1306.