Schellenberg, M. P., Biligetu, B. and Wei, Y. 2013. Predicting seed germination of slender wheatgrass [Elymus trachycaulus (Link) Gould subsp. trachycaulus] using thermal and hydro time models. Can. J. Plant Sci. 93: 793-798. Slender wheatgrass [Elymus trachycaulus (Link) Gould subsp. trachycaulus] is a native caespitose grass used for forage production and reclamation. The objective of this study was to quantify seed germination requirements of slender wheatgrass using thermal and hydro time models. Slender wheatgrass, San Luis, had a base temperature (T_b) of 9.48°C, and required 946.8°C h to reach 50% of seed germination. Seed germination of San Lius occurred at a temperature range of 10-30°C, with the highest germination rate being achieved at 20°C, and the highest final germination percentage being achieved at 25°C. At 20 and 25°C, San Luis had a hydro time constant of 61 MPa h, and a median base water potential of approximately 1.0 MPa, but the germination had low uniformity in reduced water potentials. Final germination was reduced at or lower than -0.6 MPa. Compared with many other cool-season native grasses of Northern Great Plains, a relatively warm temperature would be necessary for uniform seedling establishment of this grass. In reclamation seeding, the seedling emergence could reach the highest level at a temperature of 25°C.