Seed priming has been suggested to improve germination performance under temperature or water stress. The objective of this study was to develop an optimal osmopriming protocol for spinach (Spinacia oleracea L. cv. Bloomsdale) seeds and examine its effect on the germination performance at suboptimal and supraoptimal temperatures, and under water stress. Standard germination tests at optimal germination temperature (10°C) was conducted to evaluate performance of 'Bloomsdale' spinach seeds primed in sixty different priming treatments arising from various combinations of osmoticum (PEG 8000 concentration), priming temperature and priming duration. Germination performance was evaluated by final germination percentage, germination rate, and uniformity. An optimal priming protocol was selected and used to test seed germination performance at suboptimal (5°C) and supraoptimal (20°C) temperatures, and three levels of water stress (-0.8,-1.2, and-1.6 MPa). Priming at-0.6 MPa at 15°C for 8 d was the optimal protocol for osmopriming 'Bloomsdale' spinach seeds. This treatment also improved seed stress tolerance by improving germination performance at 5 and 20°C, and water stress of-0.8 and-1.2 MPa.