Cold -> Warm -> Cold moist stratification (Double dormancy)

Seeds need cold, moist period (winter) followed by a warm, moist period (summer) followed by a 2nd cold, moist period: Sow outdoors and allow 2 years or longer to germinate. To artificially start this stratification process, follow the instructions for Germination Code C for 60-90 days, then store in a warm (about 80°F) place for 60-90 days, followed by a 2nd cold period in the refrigerator.