This study examines the role of various environmental factors, viz. salinity, water potential, alcohol, potassium nitrate, gibberellic acid, and root exudates of neighbouring Lolium angustifolius species on seed germination, and root growth of annual ryegrass (L. rigidum). According to a statistical model, a total of 20% seed was germinated at 100 mM of sodium chloride solutions suggesting that the species is moderate to high levels of salinity tolerant. Moderate to high levels of water stress did not inhibit seed germination of L. rigidum, and 15% seeds still germinated at − 8 MPa water. Germination process of non-germinated seeds due to salt stress was not accelerated by gibberellic acid, but about 30% seed germination was increased by 0.02 M potassium nitrate treatment. The hormesis model suggests that concentrations of potassium nitrate more than 0.04 had no effect to enhance seed germination. Seeds of L. rigidum were successfully germinated under a temperature range between 10 and 30 °C. A separate laboratory experiment determined that germination was not affected by root exudates of L. angustifolius but had a significant effect on seedling roots of L. rigidum, where density by variety had a major effect on the root growth of L. rigidum. At 20 seedlings of L. angustifolius, about 80% root growth of L. rigidum was controlled and 60% roots of L. rigidum showed bent or curved growth. These results showed that L. rigidum may possess a wide range adaptive mechanism to different environmental stress.