Urban green space (UGS) has been proven to be essential for improving the health of residents. Local governments thus need to provide attractive UGS to enhance residents’ wellbeing. However, cities face spatial and finanical limitations in creating and managing UGS. As a result, greening plans often fail or are postponed indefinitely. To evaluate whether informal urban green space (IGS) can supplement existing UGS, we conducted a questionnaire survey of 567 residents in Ichikawa (Japan), a city currently providing only 3.43 m² green space per capita. In particular, we analyzed how residents’ existing green space activities affect IGS perception, as it may be difficult to recognize IGS as greenery because it is not an officially recognized space for recreation. Results show that residents took a favorable stance towards IGS, but perception differs depending on their green environment exposure. Residents who are frequently exposed to green environments in their daily lives highly recognized the environmental improvement aspects of IGS and significantly perceived spatial accessibility as an advantage of IGS. Willingness to participate in conservation activities of UGS was linked with a likelihood of recognizing IGS as UGS. Our results encourage understanding IGS as supplementary green space taking into account the attitude of residents to UGS, and contribute to introducing the IGS discourse into green space planning.

Multitudinous studies about urban green space (UGS) reveal that designed and managed UGS may provide not only social, environmental, and economic benefits for cities, but also mental, physical, and physiological benefits for their residents. However, past studies have focused on widely recognized green spaces in urban areas such as parks, gardens, and forests. Wasteland, wilderness, and unplanned in-between margins, which have been called informal green space (IGS), could provide supplementary green space. This study explores IGS in Ichikawa City, a post-industrial satellite town of Tokyo with scarce UGS, by addressing the following questions: (a) What types of non-standardized and unsystematised green space exist in the target area? (b) How is IGS in the target area perceived? (c) Could IGS be considered supplementary green space for the city? Using a systematic land use survey, we identified nine types of IGS in Ichikawa City that accounted for 6.35% of total land use. A questionnaire survey showed that undergraduate students recognize the existence of IGS in their neighbourhood, perceive multiple benefits and see especially street verges, unimproved land and water verges as potential supplementary green space. We conclude that IGS can serve as a supplementary green space and discuss how IGS might be integrated into green space planning to improve residents’ well-being.

Background and objective: As urbanization accelerates, urban areas are significantly contributing to greenhouse gas emissions worldwide. Artificial green spaces, such as green roofs, have emerged as vital strategies for mitigating urban carbon emissions while providing essential ecosystem services. However, the existing research in this area predominantly addresses the carbon sequestration potential of vegetation, leaving the role of soil materials in artificial ground systems underexplored. This study aimed to identify optimal material compositions and blending ratios for Artificial Soil Mixes (ASMs) that enhance carbon reduction while satisfying essential plant growth requirements.Methods: Eight soil materials frequently used in artificial greening —bottom ash, biochar, zeolite, peat-moss, carbonized rice hull, humus, vermiculite, and cocopeat—were blended into four distinct ASMs (ASM_A, ASM_B, ASM_C, and ASM_D). Each ASM was assessed based on its (1) physicochemical properties, (2) elemental composition, and (3) plant growth performance.Results: ASM_A exhibited comparable or slightly superior growth to the control soil, likely due to its high organic matter content and cation exchange capacity (CEC). ASM_D demonstrated the highest carbon content (27.60 wt%) among the blends, highlighting its significant potential for long-term carbon sequestration. However, its lower nitrogen and phosphate contents limited its effectiveness during early plant growth stages.Conclusion: This study contributes by developing lightweight artificial soil mixes that simultaneously support basic plant growth and enhance carbon reduction. For improved germination and initial plant growth, ASMs with higher available phosphorus and organic matter contents are recommended. Conversely, ASM_D, which is rich in recalcitrant carbon, presents greater advantages for long-term carbon mitigation. These findings underscore the necessity of further research to refine soil blends that optimally balance plant growth and carbon sequestration potential in artificial green spaces such as rooftop gardens.