Heavy metal contamination poses significant risks to plant germination and early seedling development. This study investigated the effects of different heavy metal types (Cd, Hg, Cr, Pb, Ni), concentrations (0, 100, 200, 400, 800 mg L⁻¹), and plant species (sainfoin, common vetch, and alfalfa) on seed germination parameters and seedling growth traits. The experiment was conducted under controlled laboratory conditions at the Department of Field Crops, Faculty of Agriculture, Akdeniz University. Results revealed that heavy metal type, dose, and species, along with their interactions, significantly influenced relative germination ratio, relative germination index, relative vigor index, relative shoot and root length, as well as fresh and dry biomass accumulation. Among metals, Cd and Hg exhibited the strongest toxicity, markedly reducing germination rates, seedling vigor, and biomass, while Cr, Pb, and Ni caused less inhibition. Species responses varied, with sainfoin and common vetch showing higher tolerance and maintaining better growth performance under metal stress compared to the more sensitive alfalfa. Dose-dependent declines were evident across all traits, highlighting the severity of heavy metal stress at elevated concentrations. These findings emphasize the critical role of species selection for phytoremediation and sustainable cultivation in contaminated soils. Further investigation into the physiological and molecular mechanisms underlying metal tolerance could support improved management strategies in metal-impacted environments.