We carried out a life cycle assessment to model the potential for alternative household vegetable gardens (AHHVGs) to mitigate global climate change by reducing greenhouse gas emissions (GHGE) for Santa Barbara County, California, USA. Our model included changes in GHGE due to the effect of creating an AHHVG for five components: reduction of lawn area due to replacement by the AHHVG; reduction of vegetables purchased from the conventional agrifood system due to replacement by vegetables produced in the AHHVG; reduction in amount of greywater exported to treatment facilities due to diversion to irrigate the AHHVG; reduction in amount of household organic waste exported to treatment facilities due to diversion to composting at the household level for application to the AHHVG; and composting organic household waste for use in the AHHVG. We found that AHHVGs could reduce emissions by over 2 kg CO2e kg⁻¹ vegetable, but that results were sensitive to the range of values for the key variables of yield and alternative methods for processing household organic waste. In our baseline scenario (50% of single-family households with an 18.7 m² AHHVG, providing 50% of their vegetable consumption), AHHVGs contributed 3.3% of the GHGE reduction goals of unincorporated Santa Barbara County for 2020, 0.5% of the goals for the City of Santa Barbara for 2050, and by extrapolation, 7.8% of the goals for California for 2020. Our results could provide an incentive for governments to include support of AHHVG as part of climate mitigation strategies, and for households to grow vegetables in AHHVGs to address climate change.