How Tree Seeds Grow
Trees grow from seeds in one of two ways. One way is when a seed gets embedded in the soil, either because it falls from the parent tree or because a gardener plants it. Either will result in the seed having the necessary period for dormancy and then germinating when the temperature warms in the spring. The other way is "assisted germination" and involves placing the seed into environments that simulate what would happen in nature and therefore force the seed to germinate before planting.
For natural germination, a gardener plants the tree seeds in autumn without taking any special steps to aid germination. Planting the seeds at the proper depth is important because if the seed is too deep within the soil, it may not germinate the following spring. The planted seeds have a stratification period over the winter, and when the weather warms in spring, the germination process starts. Stratification is the process of subjecting seeds to either cold or warmth to create the dormancy period seeds need before germination. This process delays the seeds from germination in the autumn before the weather gets cold in the winter.
Assisted germination is a process of artificially subjecting tree seeds to the different stages of the natural germination process. The stages include scarification and stratification. Not every tree seed requires these stages, however. Scarification is breaking the seed coat so that the embryo can burst forth from the seed coat more easily. Seeds with hard outer coats often require scarification. Soaking the seeds in room-temperature water for 24 hours or rubbing the outside of the seed with sandpaper are two common scarification methods. Stratification involves subjecting the seeds to a warm or cold period prior to germination. Cold stratification mimics the seeds sitting in the soil over the winter. The seeds are placed in a plastic bag filled with damp peat moss and kept in the refrigerator for several weeks. Warm stratification mimics the seeds sitting in muddy soil over the summer prior to sitting in cold soil over the winter. Seeds that are in deep dormancy or that have a extremely hard seed coat may need warm stratification prior to cold stratification. For warm stratification, place the seeds in a plastic bag and keep them in a location with a temperature between 72 and 86 degrees. After the warm stratification, proceed to the cold stratification process.
Planting the Seeds
Plant the seeds indoors in individual containers or a seeding tray. The seeds must be planted at the proper depth, which is usually quite shallow. Consult planting recommendations for the specific type of tree seed to make sure you plant the seeds at the proper depth. Keep the potting soil moist during the germination process. Some tree seeds benefit from increased humidity. Achieve this by placing a plastic bag with ventilation holes over the germinating seeds. Watch for the seeds to sprout and move them to a sunny location after germination. Plant the seedlings outdoors after they are well established and the weather and soil are warm.