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Why do many temperate conifer seeds need a cold, moist winter period before germinating?

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Tall giant sequoia trees with reddish bark and thick trunks rise closely together in a dense forest at Sequoia National Park, California. — Tree A stand of giant sequoia trees (*Sequoiadendron giganteum*) in Sequoia National Park, California.

Many temperate conifer seeds require a cold, moist winter period before they can germinate because they possess a type of dormancy that can only be overcome through a process known as afterripening.1

During this period, the embryo undergoes essential physiological changes that allow it to break its dormant state. In nature, this is achieved through exposure to cold and moisture over the winter months. If these specific environmental requirements are not met, the seeds may fail to germinate or produce abnormal seedlings.12

To ensure more uniform and faster germination, horticulturists often replicate these conditions through a procedure called stratification. This involves keeping the seeds moist and at cool temperatures (typically 0–10 °C or 32–50 °F) for a period ranging from one to six months, depending on the species. This process is vital for many conifers, such as pines and hemlocks, ensuring they only begin to grow when conditions are favorable for survival.12