Warm -> Cold moist stratification

In order to germinate, seeds need a warm, moist period (summer) followed by a cold, moist period (winter): Sow outdoors in spring and allow one full year for germination. To artificially start this stratification process, mix seeds with horticultural-use medium, place mixture in a labeled, sealed, plastic bag and store in a warm place (about 80°F) for 60–90 days. Then place in your refrigerator (33–40°F) for 60–90 days before sowing.