The COVID-19 pandemic has not only jeopardized people's physical health, but also put additional strain on their mental health. This study explored the role of indoor natural elements (i.e., green plants) in relieving individuals' mental stress during a prolonged stressful period. A pilot and three formal studies examined the effect of indoor green plants placed in living and working environments on people's perceived stress during the pandemic and further uncovered its underlying mechanism emphasizing a mediating role of emotion. The pilot study confirmed that the severity of the pandemic positively correlated with individuals' level of stress. Study 1 then demonstrated that indoor green plants in people's living environments might reduce their perceived stress during the pandemic, which is referred to as the "plant effect". Study 2 repeated the plant effect in a field experiment conducted in a working environment and Study 3 revealed a mediating role of positive emotion. This study provides preliminary evidence for the mitigating effect of indoor green plants on individuals' mental stress during the COVID-19 pandemic period. The indoor green plants placed in living and working environments may elicit positive emotion, which in turn reduce people's mental stress. In addition, our results reveal that growth status of the indoor green plants affected the plant effect as well.
Keywords: COVID-19 pandemic; green plants; growth status; mental stress; positive emotion.