Many seeds, particularly those of temperate plants, undergo a dormant period during winter, so that they don't germinate until conditions are favorable in spring. The cold stratification process essentially tricks these seeds into thinking they have endured a winter, making them ready to sprout once warmer temperatures return.

While sitting in a moist and cold environment, such seeds gradually lose chemical inhibitors that prevent germination. Their seed coats soften, allowing water and oxygen to enter the seeds more easily. The cold also stimulates the production (or activation) or some enzymes needed to start using food resources inside the seed. Some growth hormones begin to increase, and certain genes are believed to begin to be expressed.

All of this activity prepares the seed for vigorous growth once it fully exits dormancy.