The ex situ conservation of recalcitrant seeds has been one of the biggest challenges in seed technology. Different strategies have emerged in recent years and among these strategies, osmotic conditioning at controlled temperatures has shown excellent results. Therefore, the objective of this research was to store recalcitrant seeds of E. uniflora through osmotic conditioning in order to reduce the metabolism of these seeds and extend their storability. The seeds were stored at temperatures of 10 and 25 °C in PEG solutions at 0.0 (water), -0.5, -1.0, -1.5, and -2.0 MPa, as well as without moistening, for 3, 6, 12, and 18 months. There was a reduction in metabolism in the treatments with PEG, and seed viability was maintained after 18 months at 25 °C and -1.5 MPa.