Community gardens as neighborhood compost sites: A cost-benefit analysis

Background/Question/Methods

Organic materials account for one quarter of the solid waste stream in the Twin Cities Metropolitan Area, and the City of Saint Paul has set a goal of increasing composting participation among its citizens.  Also in recent years, the popularity of urban farming has increased rapidly in the Twin Cities, and there are at least fifty-nine community gardens in Saint Paul alone.  As urban soils are often degraded and contaminated, these gardens create a demand for compost.  We investigated the feasibility of using community gardens as neighborhood composting sites in Saint Paul.  We estimated the amount of food waste that could be processed in each garden’s compost pile based on revised state guidelines, and calculated the number of people whose food waste production could be processed at each garden.  We then used a GIS analysis to compare food waste production and composting capacity citywide.  We conducted a series of interviews with experts from state and local government agencies, private industry, and community groups to identify potential issues of concern.  Finally, we surveyed community garden managers across the Twin Cities to quantify their needs for compost, and their perceptions of the benefits and problems that this proposal would create. 

Results/Conclusions

We calculated that each 80 cubic yard compost pile could process approximately 13,000 kg of food waste annually, roughly the amount produced by 334 people.  Community gardens citywide would be able to process approximately 7% of the household food waste produced in the city, although the density of community gardens varies across the city and some areas could have all of their composting needs met by their neighborhood community garden.  Our survey results indicated a strong demand for compost from community gardens, and garden managers also indicated that neighborhood composting would be beneficial by generating community involvement in the garden, preventing food waste from ending up in a landfill or incinerator, and by keeping compost in the neighborhood as opposed to transporting it to a regional composting facility.  The amount of work required in order to manage these compost piles, and the potential for contamination, odor, and pest problems were identified as the greatest impediments.  Our results suggest that neighborhood-scale composting using community gardens could be part of a comprehensive plan for increased organics recycling, if the city provides resources for educating citizens and for supporting compost managers.  A next step would be a carefully implemented neighborhood pilot study.