Nature based solutions are amongst other practices that transition initiatives work with when intervening in their place and change its fabric. Focusing on the actors establishing, driving and scaling these solutions in and across cities, we come to evince that nature-based solutions have transformative social impact since they mediate new social relations and new social configurations contributing to social innovation in cities, and change nature perception and human-nature relations in urban contexts. We built from evidence in three city-regions that over the past years they saw the proliferation of community-based and policy-based initiatives with the aim to improve sustainability, livability and the aspiration to foster inclusivity and social justice in their cities: the city of Dresden in Germany, the city of Genk in Belgium and the city-region of Stockholm in Sweden. We will elaborate on the different ways nature based solutions as practices of transition initiatives in cities get scaled and contribute to accelerating sustainability transitions in these city-regions. In line with this, we will draw cross-case lessons for urban planning on the tensions transition initiatives that experiment with and institutionalize nature-based solutions in their cities face when actively pursue acceleration strategies and pathways to scale.