Stratification of seeds means chilling under moist, not wet, conditions to prompt the germination of dormant seeds. (A dormant seed is one that does not germinate immediately when exposed to normal germination requirements such as adequate temperature, sufficient oxygen, and appropriate moisture).

Stratification can be accomplished in a refrigerator or outdoors, although it is better to avoid freezing the seeds during the process. The suggested temperature range (see Griesbach) for daylily seed stratification is 0°C (32°F) to 10°C (50°F), with four to eight weeks duration being sufficient. Chilling dry seeds does not achieve the same effect. Stratification causes the seeds to germinate at more or less the same time upon removal from chilling conditions, instead of spread out erratically over weeks or even months. While many daylily seeds benefit from stratification by germinating more evenly and quickly, not all daylily seeds are dormant and non-dormant seeds will germinate promptly without stratification.

Griesbach, Robert A., and Paul D. Voth. “On dormancy and seed germination in Hemerocallis.” Botanical Gazette 118.4 (1957): 223-237.
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The American Daylily Society