Producers may be able to improve growth of cover crop mixtures by selecting species to occupy different levels (zones) in the cover crop canopy. This suggestion is based on a study where we compared four cover crop treatments, comprised of one, three, six and nine species, for biomass production. Oat, dry pea and oilseed radish were present in all multi-species mixtures. Treatments were established in August, following spring wheat harvest. Biomass was harvested 9 weeks later. The most productive treatment was the oat–dry pea–oilseed radish mixture. Species of this mixture occupied different zones in the canopy and minimized interspecies competition to improve production. Cover crop mixtures of six and nine species produced 24% less biomass, which we partially attribute to unequal distribution of species in zones of the canopy. This suggestion with canopy architecture could be tested further with other cover crop species to quantify its impact.