Abstract Nature connectedness can promote pro‐environmental behaviour and psychological well‐being, but little is known about how nature connectedness can be strengthened. Interventions that seek to enhance nature connectedness by promoting direct nature contact may be impractical because urban areas often lack opportunities for interactions with nature in the daily lives of people. This study examines the effects of a gratitude journal exercise on nature connectedness, psychological well‐being, and engagement in wildlife gardening. Participants (N = 114) were either asked to write down daily three things relating to nature that they were grateful for over a 14‐day period or they were assigned to one of two control groups (a traditional gratitude condition and an activity list condition). Compared to the two control groups, there were no significant differences in any of the outcome variables during the 14‐day period and at 1‐week and 3‐month follow‐ups. However, significant increases in all those outcome variables emerged independent of the group. Qualitative data analysis suggests that the journal exercise promoted increases in the outcome variables by generating self‐knowledge as well as positive emotions and attitudes. Moreover, participants noted that the journal activity made them think about nature in new ways, presumably through answering daily survey questions on nature connectedness. We suggest that the mere activity of regularly reflecting on one's relationship with nature may increase nature connectedness. Interventions that encourage people to contemplate the interconnectedness between themselves and nature could be a viable strategy to strengthen human–nature relationships, especially in urban areas that lack opportunities for interactions with nature. The findings of this study can inform future research concerned with the processes of strengthening nature connectedness and the design of interventions that employ nature‐based journal exercises. Read the free Plain Language Summary for this article on the Journal blog.