Urban parks and gardens may be failing to meet the diverse "nature needs" of a growing global urban population. Informal urban greenspace (IGS) such as vacant lots, street or railway verges and riverbanks may provide space for unstructured recreation and nature contact. Yet we know little about residents' relationship with IGS outside of Europe and North America, what factors influence IGS use and evaluation, or what role geographic and cultural context play. Our paper combines qualitative and quantitative methods to examine how residents in Brisbane, Australia (n=123) and Sapporo, Japan (n=163) perceive, evaluate and use IGS. Using statistical methods (e.g. correlation analysis) we analyzed what factors influence how respondents interact with IGS, including the amount of formal greenspace within 500m of survey locations using a GIS buffer analysis. Results were tested for differences and similarities between the cities. We found that respondents knew of IGS in their neighborhood (>80%), appreciated and used it (>30%), but more respondents in Brisbane used and appreciated IGS. The influence of demographic factors and local formal greenspace area was limited, but respondents' attitude towards urban nature was correlated with IGS evaluation. Littering was perceived as IGS' most common problem (90% of respondents), but was reported by <20% of IGS users. Geographic (e.g., IGS type prevalence) and cultural (e.g., human-nature relationship) contexts represented potential influence factors. We argue that the liminal nature of IGS (e.g., liability) management poses a challenge traditional greenspace planning. To address this problem, further research should explore participatory management approaches.