Leymus arenarius is used to stabilize the extensive areas of eroded volcanic sand in Iceland, both inland and on the coast. It has been reported previously to produce seeds of generally low viability. We investigated the potential for seed dormancy and the responses of germination to temperature, light and salinity, as part of a re-assessment aimed at improving reclamation procedures. Contrary to previous reports, high rates of germination could be obtained under certain conditions. All caryopses were soaked in water (24 h) and stratified for 2 weeks (5 °C) before the subsequent germination tests. Constant temperatures or exposure to light resulted in very poor germination. Close to 100% germination could be obtained within 2 weeks in continuous darkness, under alternating temperatures with an amplitude of 10-20 °C on a 12 h cycle; high day temperatures appear to be important. Diurnal fluctuations in temperature of this order occurred under average weather conditions in the black, volcanic sands in Iceland during the growing season (May-Sep.). The dark requirement is interpreted as a selective response to the adverse conditions for establishment at the surface of the sand; the alternating temperature requirement may be a response to ensure dormancy under deep burial with accreting sand, although it could have a role in gap-sensing under established canopies. Scarification, surface sterilization and treatment with n -butanol or KNO3 were all generally ineffective in promoting germination. Nearly all caryopses that did not germinate, in all treatments, remained viable. Caryopses of coastal populations of Leymus arenarius showed significantly higher total germination and more rapid germination in 100 mmol l-1 and 300 mmol l-1 NaCl solutions than inland populations. The inhibition of germination by salinity was an osmotically enforced dormancy effect rather than a lethal, toxic one; caryopses that had not germinated in saline solution generally were able to germinate subsequently, when transferred to non-saline conditions.