Trees that drop their leaves in the autumn and re-foliate in the spring. Culture: Cold Stratification of Tree Seeds. When seed is sown in the fall, this cold stratification occurs naturally though the winter. Seed can also be cold stratified without planting outdoors. Using this cold/moist stratification method, which is preferred by most tree seeds, mix the seed with a moistened soil-less medium in a container or planting tray, seal the container/tray shut with lid or wrap in plastic bag and place it in a refrigerator, an unheated garage or outdoor coldframe for 2 months. When you remove from the cold, place under grow lights indoors or in the coldframe for spring warmth/sun to warm up soil and encourage germination.