Mechanical means, such as a metal file or coarse sandpaper, can be used to break the seed coat. Treatment with boiling water has also been successful for a number of tree species. In nature, the seed coat may be broken by microbial action, passage of the seed through the digestive tract of a bird or other animal, exposure to alternate freezing and thawing, or fire. The seed of many tree species will not germinate until they have been exposed to cool temperatures and moist conditions for several weeks or months. Winter weather in Iowa provides the necessary conditions to break dormancy.
Gardeners can accomplish the same results by a process called stratification .
Suitable containers include coffee cans, plastic jars, and cottage cheese containers. Seed can also be stratified in plastic bags. Stratify the seed in the refrigerator. The seed of some trees, such as redbud, have hard impermeable seed coats and dormant embryos. They require both scarification and stratification for germination.