With food security increasingly seen as an urban concern, urban agriculture (UA) has emerged as one strategy for improving access to healthy, affordable food within cities in the Global North. This research evaluates the contributions of three types of urban gardens in Santa Clara County, California, to food security. Survey, interview and harvest data were collected from home gardeners, community gardeners and gardeners participating in community food security (CFS) programs, which provide low-income families with the materials and training to grow their own vegetables. To assess food security we use a multi-dimensional framework that encompasses food availability, accessibility, nutritional adequacy and cultural acceptability as well as agency within the food system. Over the summer of 2015, median garden production ranged from 26 kg for participants in CFS programs to 56 kg for home gardeners. All garden types produced enough produce for at least one adult to consume the number of cups of vegetables recommended by federal nutritional guidelines. Gardening also increased some low-income gardeners’ access to healthy food, allowing them to have the diet they wanted—one high in organically grown vegetables—but could not otherwise afford to purchase. Interviews showed that gardeners do not think of cultural acceptability strictly in terms of the presence of certain types of cultural crops; they also articulated a broader set of values concerning the environmental and social conditions of food production. At all income levels, gardeners frequently described a set of food values related to knowledge, control, trust, freshness, flavor, organic production methods and sharing, which they were able to enact through gardening. Taken together, these findings demonstrate the nutritional contributions that urban gardens make but also highlight the importance that low-income gardeners place on having food that aligns with their cultural and ethical values and being able to exercise greater autonomy in making food choices. In conclusion, we suggest that more robust, holistic assessments of UA's contributions to food security will include the subjective aspects of food as well as quantitative measures related to food production.