This paper studies whether the absence of locally adapted seed varieties constrains the productivity and incomes of farm households residing in small, agro-ecological niches. We empirically examine the disruption of the maize seed market in Western Kenya that took place when public sector foundation breeding and social impact investment capital came together and allowed a local seed company to expand and target a niche area with adaptively-bred maize varieties. The three-year randomized controlled trial reveals that these seed varieties increased farmer yields and revenues, both for better-resourced farmers (who used non-adapted hybrids and fertilizer prior to the intervention) as well as less well-resourced farmers (who did not). This theoretical and empirical evidence suggests news ways for thinking about seed systems in areas typified by high levels of agro-ecological heterogeneity.