Temperature Limits for Seed Germination in Industrial Hemp (Cannabis sativa L.)

Industrial hemp (Cannabis sativa L.) as a grain and fiber crop is experiencing a resurgence in North America. Due to governmental prohibition, there has been limited information on regional agronomic production systems including basic information on seed germination. This study was initiated to provide basic information on the relationship between temperature and germination in hemp seed. Germination was measured at constant temperatures ranging from 3 to 42 degrees C. Cardinal temperatures were determined for two industrial oil crop hemp cultivars ('Georgina' and 'Victoria'). The optimal germination temperature indicated by a high mean germination percentage and rate was between 19 and 30 degrees C. Optimal (29.6 degrees C), base (3.4 degrees C) and ceiling (42.6 degrees C) temperatures were calculated from a linear regression of the germination rates to reach 50% germination for each temperature. The thermal time for 'Georgina' and 'Victoria' to reach 50% germination at suboptimal temperatures was 694 and 714 degrees C h, respectively. The osmotic and solid matrix-primed hemp seeds germinated faster than the untreated seeds, but the final germination percentages were not different. The primed seeds germinated faster at supraoptimal temperatures but did not impact final germination percentages in the thermally inhibited seeds.