Kludze, H., Deen, B., Weersink, A., van Acker, R., Janovicek, K. and De Laporte, A. 2013. Impact of land classification on potential warm season grass biomass production in Ontario, Canada. Can. J. Plant Sci. 93: 249-260. This paper examines the land base of southern Ontario to determine the capability of land classes for growing two warm-season grasses, switchgrass (Panicum virgatum) and miscanthus (Miscanthus spp.), and discusses implications of a provincial biomass industry strictly based on biomass grown on marginal lands. The development of a biomass energy industry is a priority for many regional governments in Canada as a means to reduce fossil fuel use and improve environmental quality. Biomass productivity of the two crops was determined by assuming percentages of arable land area by quality that could be allocated to them: biomass productivity on “prime lands” was assumed to be higher than those of “marginal lands”. Our analysis indicates that Ontario has an adequate land base for producing miscanthus and/or switchgrass biomass to meet and surpass diverse competitive uses without significantly affecting food crop supply. Locations of marginal lands are scattered in the province and the feasibility of establishing a provincial biomass industry strictly based on biomass grown on these lands may not be economically sound or practical. A relatively small percentage of prime lands is required to achieve substantial biomass production with lower costs of production, and perhaps greater environmental benefit.