How does stratification help cold-requiring seeds germinate more evenly?

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Cluster of bright red seeds emerging from the cone-shaped fruit of a magnolia grandiflora, surrounded by large, glossy green leaves. — seed Fruit and seeds of the southern magnolia (*Magnolia grandiflora*). The fruit is an aggregate of follicles, and each follicle bears a single red seed.

Stratification is a practical procedure used to promote faster and more uniform germination in seeds that require cold conditions to overcome dormancy.1

Many seeds, particularly those from certain forest trees, shrubs, and fruit trees, possess embryos that remain dormant even under favorable growth conditions. These seeds must undergo a series of physiological changes known as afterripening before they can germinate.1

During the stratification process, seeds are kept moist and exposed to cold temperatures—typically between 0–10 °C (32–50 °F)—for a period ranging from one to six months. By placing the seeds between layers of materials such as sand, sawdust, sphagnum, or peat, the procedure ensures that the cold requirement is met consistently across the seed batch. This controlled environment facilitates the necessary afterripening changes, allowing the seeds to break dormancy and germinate more synchronously rather than sporadically over several years.1