Stimulating green innovation is crucial for sustainable development. This study examines the impacts of green knowledge relatedness and complexity on firm-level green innovation using data from 13,492 German manufacturing firms during 2011-2019. We construct regional green knowledge relatedness and complexity measures using OECD-REGPAT data and firm-level characteristics from Orbis Intellectual Property and Orbis data. By considering knowledge relatedness between green and green technologies, as well as green to non-green technologies, we reflect the importance of both in promoting future green innovation. Our findings indicate that regional green knowledge relatedness significantly enhances firms' green innovation production, reinforcing regional path-dependence. Moreover, high-technology firms benefit more from the joint effect of green knowledge relatedness and complexity, unlike low-technology firms. This study provides a nuanced understanding of how regional green knowledge characteristics influence firm-level green innovation. It highlights the importance of tailored policy measures to enhance regional green technological capabilities and foster green innovation. Policymakers should focus on developing place-based strategies that leverage existing related knowledge and complex knowledge to maximize green innovation benefits. This research also contributes to the ongoing debate on path-creation versus path-dependence in economic geography and offers practical insights for fostering sustainable technological advancements.