The evidence is piling: contact with nature is good for our health. But today's reality is that nature is not by default part of our lives, particularly not for citizens living in deprived urban neighborhoods. One strategy to increase nature contact locally, is through green citizen initiatives: gardens and urban agriculture projects initiated and run by citizens. We studied eight green citizen initiatives in Arnhem and Nijmegen in The Netherlands to explore what well-being benefits residents experience with regards to their participation in local green initiatives. This paper presents the methods developed to measure well-being outcomes, plus the first results. We conducted a questionnaire among 109 participants of green citizen initiatives in 2020. We found that participation in green initiatives creates positive experiences for six dimensions of well-being: meaningful involvement, personal development, social connection, sense of ownership, sense of safety and trust, and healthy lifestyle. Participants feel part of the initiative, gain social contacts and get to spend time outdoors. The greatest well-being benefit of green initiatives turned out to be a sense of safety and trust. We found less evidence of increased healthy food intake and other lifestyle aspects. This raises the question whether participants have already adopted relatively healthy lifestyles and/or whether the green initiatives attract a certain group of residents-and other groups not. With our study we provide a method and the first evidence on the value of green citizen initiatives as a bottom-up strategy to improve the health and well-being of citizens in deprived urban neighborhoods.