Rapid global population growth increases the human demand for food. Reliance on the high input of agrochemicals in agricultural production has been shown to be unsustainable and cost ineffective. The combination of planting and breeding can maximize the utilization of agricultural resources. A novel crop–earthworm coculture model has been gradually practiced in urban agriculture in eastern China. We conducted a four-year successive study of taro–earthworm coculture farming to determine the ecological and economic benefits of the model. Our results indicated that earthworm activities in the taro–earthworm coculture system increased taro yield, economic value and net income by depleting the weed seed bank, mitigating weed infestation, and reducing the need for weeding. Compared with those in mono-taro farming, the four-year mean seed bank densities of total weeds, grassy weeds and broadleaf weeds in taro–earthworm farming decreased by 37.1%, 44.4% and 32.2%, respectively; the weed density, biomass, species richness and diversity and need for weeding decreased by 54.1%, 48.3%, 20.8%, 8.2% and 39.7%, respectively; and the taro yield, economic value and net income increased by 19.7%, 19.7% and 50.7%, respectively. Our study suggests that earthworm activities provide ecosystem services in agricultural systems, and the coculture of taro and earthworms enhances crop production by mitigating weed infestation and improving environmental quality.