Plants that are double dormant require a unique sort of layering or stratification in order for their seeds to germinate. The seeds of these plants must have a period of warmth and moisture, followed by a cold spell. Both the seed coat and the seed embryo require this double dormancy if they are to germinate. In nature, this process usually takes two years. Some well-known plants that live the life of double dormancy include lilies, dogwoods, junipers, lilacs, and tree peonies.