Rapidly elongating Bromus tectorum and Taeniatherum asperum roots penetrated the soil ahead of Agropyron spicatum roots and used available moisture. In contrast, Agropyron desertorum roots penetrated the soil almost as rapidly as B. tectorum and T. asperum and remained in favorable moisture. These differences in root penetration resulted in lower leaf water potentials and poorer survival in A. desertorum. The results suggest that in areas where root growth occurs at low temperatures and where lands are infested with B. tectorum and T. asperum, seedlings of A. desertorum would be more successful than seedlings of A. spicatum.