Stratification of a seed is a horticultural technique that simulates the natural conditions that some seeds need to experience before they can germinate. Many seeds have a dormancy phase that prevents them from sprouting until they are exposed to cold and moist environments for a certain period of time. This process can be done artificially by placing the seeds in a medium such as sand, peat, or vermiculite and refrigerating them in a plastic bag or container. The duration of stratification varies depending on the plant species, but it can range from a few weeks to several months. Some seeds even need two periods of stratification and warming before germinating. Stratification helps to break down the hard seed coat and trigger the growth of the embryo inside the seed.