Rising incidences of waterlogging and salinity, particularly in extensive livestock farming areas, pose increasing challenges to plant growth. This study investigated the morphological growth responses and tolerance of 39 Festuca arundinacea accessions to these stresses, with tolerance quantified by the relative growth rate under stress versus control conditions. Notably, more productive accessions under normal conditions also showed greater stress tolerance. Waterlogging was generally well-tolerated (89–113% of control relative growth rate), without significantly altering growth morphological components as increases in specific leaf area were offset by reductions in leaf weight ratio, maintaining stable leaf area ratios. Conversely, salinity and combined saline waterlogging significantly reduced relative growth rate (56–94% of control), with a substantial variation among accessions. A decrease in specific leaf area, suggestive of thicker leaves, correlated with higher tolerance to salinity and saline waterlogging (r = 0.63). In summary, F. arundinacea displays diverse tolerance to these stresses, warranting further study into the adaptive mechanisms. Specific leaf area emerges as a potential selection marker for breeding programs targeting saline and waterlogging tolerance.