Traditional commercial mushroom (A. bisporus) production involves a two-phase composting process that may result in malodorous emissions and may take three weeks or more to complete. In recent years, researchers have been searching for cost-effective alternative substrates for mushroom cultivation that have a lesser impact on the environment. One proposed alternative is a substrate prepared from corn stover (CS) that is colonized with thermophyllic fungi such as S. thermophilum or M. thermophilum. Here we report on the growth of A. bisporus on S. thermophilum- and M. thermophilum- colonized CS and the influence of a potential contaminant (P. chrysogenum) on growth of A. bisporus. Mycelial growth was more rapid on St-colonized CS compared to Mt-, St- and Mt-colonized CS, non-colonized CS and phase II compost. Mycelial growth in non-contaminated substrates was significantly greater compared to mycelial growth in substrates contaminated with P. chrysogenum and St-colonized substrate conferred selectivity to the substrate by reducing the growth of the inoculated contaminant.