Institutional interest in citizen engagement and deliberative democracy is at an historical peak. If the goal of democratising institutions is seen as desirable for enhancing democratic resilience, going beyond good intentions requires political commitment and institutional change. How can participatory practices be mainstreamed in public institutions? Taking stock of lessons learnt in BiodiverCities, a pilot project about greening cities with citizens, the Lab is intended to be a moment of exchange & co-creation with civil servants, practitioners and citizens.