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Why do apple seeds need chilling before they germinate normally?

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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.

Apple seeds require a period of cold exposure to undergo a process known as afterripening, which is essential for normal germination.12

Even when environmental conditions such as moisture and temperature are otherwise favorable for growth, the embryo within an apple seed remains dormant. This dormancy is a biological mechanism that prevents the seed from germinating prematurely during unfavorable conditions, such as before the onset of winter.12

When the cold requirement is not sufficiently met, germination often fails or is significantly delayed, and the resulting seedlings frequently exhibit abnormal growth. To ensure uniform and successful germination, horticulturists often use a procedure called stratification, which involves keeping seeds in a moist, cold environment (typically 0–10 °C or 32–50 °F) for one to six months to simulate the natural winter conditions necessary to break this dormancy.12