The ability of seeds to imbibe water depends on the difference in water potentials between the seed and the surrounding medium, as well as seed diffusivity. The proportional moisture content and imbibition rate of Brassica napus L. 'Liberty' (canola), Setaria viridis (L.) Beauv. (green foxtail), Brassica kaber (DC.) L.C. Wheeler (wild mustard), and Avena fatua L. (wild oat) were examined over time in water and osmotic solutions of -0.5 and -1 MPa. Average imbibition rate of wild oat was significantly higher than that of all other species studied, while the average imbibition rate of green foxtail was significantly lower than that of all other species studied. Differences between imbibition rates may have been caused by differences in seed size or seed diffusivity. Wild mustard and canola had the highest proportional moisture content at 25 h and were the only two species to achieve greater than 80% germination within this time frame. Germination was reduced in osmotic solutions of -0.5 and -1 MPa compared with water for all species. Species differ in their ability to imbibe water as well as their ability to germinate at lower seed moisture contents.