Microclimate and growth advantages in the ‘Three sisters’ planting food system in an urban garden

Background and aims: Efficiently and sustainably growing food requires that we understand the ecological effects that plants have on the environment and on neighboring crops. Densely planted crop species will often be resource-limited and require artificial fertilizers to ensure maximum growth. However, positive interactions due to microclimate effects are also common between plants, and overlooked in an agricultural context. Methods: We grew the Three Sisters (Zea mays, Phaseolus vulgaris, Cucurbita pepo) in monoculture and in polyculture plots at an urban farm in Los Angeles, California. We measured plant relative growth rate every two weeks, aboveground biomass, belowground biomass, flower weight and fruit weight at the end of the growing season. We measured the microclimate conditions using temperature and humidity dataloggers mounted under the canopy of the plants. We then calculated net biodiversity effects and land equivalent ratios for all mixtures. Results: The Three Sisters polyculture did not grow more than the monoculture plots on average. However, we found the Three Sisters grew more than monocultures in high light environments when soil moisture was limiting. Microclimate temperatures were also lower when the polyculture growth advantage was greater. Conclusion: This study addresses the importance of environmental heterogeneity and vegetative microclimate feedbacks for determining polyculture growth benefits in a dry urban setting.