Seeds that have endogenous physiological dormancy often require chilling stratification to satisfy their dormancy.

Successful stratification requires seeds to be stored in a moist, aerated medium at chilling temperatures for a certain period of time.

In many cases, these seeds can be simply sown outdoors in the fall for spring emergence.

Photo of a bin with alternating layers of seeds and sand.

The term stratification comes from the old time practice of alternating or stratifying layers of sand with seeds in an outdoor structure where it would receive natural winter chilling.

In some cases, growers want to germinate dormant species for greenhouse production.

In this case, seeds are stored in a moist condition in a refrigerator until their dormancy has been satisfied.

Seeds can then be sown in a similar fashion to other greenhouse crops.

Photo of seeds being stored in a refrigerator.

The figure to the right shows a typical response to chilling stratification.

Some seeds in the population require less chilling than others to come out of dormancy, but given enough time almost all seeds will become non-dormant.

Chart showing the relationship between germination percentage and number of weeks of stratification. The percentage is virtually 0% until the 5th week, then rises steadily till week 9, when the percentage levels off at around 80%.